Keywords: marge passive, bassin intracratonique, rifting, source-to-sink, paléogéographie, l'Océan Atlantique Equatoriale, Afrique, bilan d'érosion, bilan d'accumulation passive margin, intracratonic basin, rifting, source-to-sink, paleogeography, Atlantic Equatorial Ocean, Africa, erosion budget, accumulation budget

Cette thèse présente la première étude Source-to-Sink de la marge Atlantique Equatoriale africaine au Méso-Cénozoïque. Nous avons dans un premier temps produit, à partir d'une nouvelle méthode intégrant les limites d'érosion des dépôts préservés dans les bassins et leur extension initiale minimum, une nouvelle reconstruction paléogéographique et structurale couplant pour la première fois le continent ouest africain et l'Atlantique Equatoriale au cours du Méso-Cénozoïque. Ceci nous permet de suivre l'évolution depuis 200 Ma des domaines en érosion (sources) et en sédimentation (puits) à l'échelle continentale. Nous montrons en particulier qu'au Crétacé supérieur la zone correspondait à un grand bassin intracratonique Saharien qui exportaient ses sédiments à la fois vers la Téthys et vers l'Atlantique Equatoriale. La fragmentation de ce bassin a eu lieu à l'Oligocène par le soulèvement du bouclier du Hoggar qui a isolé les petits dépôt-centres résiduels actuels. Le développement de cette topographie particulière est issu de la superposition de différentes longueurs d'onde de déformation à l'échelle continentale combinant les bourrelets marginaux longeant la marge équatoriale et un bombement de type « point chaud ».

Nous avons ensuite caractérisé, à partir de l'interprétation des données sismiques et des puits, la segmentation de la marge continentale équatoriale en segments transformants et divergents et l'architecture stratigraphique post-rift du prisme stratigraphique associée au Crétacé Supérieur. Nous montrons que les parties proximales (dépôts de plateforme et pente continentale) des prismes stratigraphiques du Crétacé Supérieur ne sont préservés que le long des segments divergents de la marge, et pas le long des segments transformants. Nous interprétons cette différence de préservation comme résultant de mouvements verticaux post-rift plus importants dans les domaines proximaux des segments transformants empêchant la préservation des termes proximaux des systèmes sédimentaires.

La caractérisation des architectures stratigraphiques post-rifts a ensuite permis la quantification des volumes sédimentaires préservés dans ces bassins de marges passives. En parallèle, de nouvelles données de thermochronologie basse-température (AFTA et (U-Th-Sm/He sur apatite) acquises à l'Université de Glasgow sur les échantillons de trois profils perpendiculaires à la marge équatoriale ont permis de quantifier l'histoire de l'érosion et les volumes dénudés sur le domaine continental au cours du Méso-Cénozoïque. Ces données montrent que le seul événement thermique majeur enregistré correspond au refroidissement lié à la dénudation d'une topographie syn-rift le long de la marge. Le bilan d'érosion et d'accumulation montre que les ordres de grandeur des volumes dénudés et accumulés sont comparables à l'échelle de la marge équatoriale au cours du Méso-Cénozoïque. Certaines périodes (Crétacé Supérieur et depuis le Miocène Supérieur), montrent cependant un excès d'accumulation qui pourrait être associé à la remobilisation de sédiments précédemment stockés dans des bassins intracontinentaux ou sur la plateforme de la marge.

List of Figures

INTRODUCTION

Les reliefs continentaux évoluent aux échelles de temps géologiques sous l'influence de l'érosion et la déformation de la lithosphère. La dynamique d'érosion des domaines orogéniques est largement étudiée dans la littérature, ainsi que ses interactions et rétroactions avec la convergence et le climat. Cependant, la dynamique de l'érosion dans les domaines non-orogéniques (ou cratoniques) reste très peu étudiée, en particulier aux échelles de temps géologiques. En effet, ces domaines sont caractérisés par un relief beaucoup plus modéré et des taux d'érosion beaucoup moins élevés que dans les chaînes de montages. Leurs contributions aux bilans sédimentaires globaux sont pourtant non négligeables, étant données les surfaces très importantes impliquées sur des durées de temps longues. Les variations de relief dans ces domaines semblent à être contrôlées par des déformations épirogéniques, de faible amplitude et de grande longueur d'onde ainsi que par les variations climatiques. La dynamique de l'érosion des domaines non-orogéniques et les volumes exportés restent à cependant encore analyser afin de comprendre la dynamique de ces surfaces continentales, et ce, à grand échelle et à long terme (x 10 Ma).

Les domaines non-orogéniques sont souvent bordés par des bassins de marges passives ou intracratoniques, dans lesquels le matériel exporté est préservé. Dans des cas simples où l'histoire des aires drainées (source area) peut être contrainte, l'histoire de l'accumulation (sink) peut être directement comparée à celle des volumes exportés (source). Les changements dans la distribution des sédiments dans les bassins et leur architecture stratigraphique peuvent donc révéler des évènements tectoniques ou climatiques affectant le domaine continental. Cette approche Sourceto-Sink a été appliquée principalement dans des contextes de marges passives (Galloway et al.,INTRODUCTION 15 L'Afrique de l'Ouest est une région d'étude pertinente pour contraindre l'histoire 'Sourceto-Sink' terre-mer en contexte non-orogénique. Elle est en effet constituée d'un craton Archéan-Protérozoïque bordé par la marge Atlantique Equatoriale où une quantité importante de sédiments clastiques ont été préservés depuis le Crétacé Inférieur. La déformation orogénique y est absente depuis 500 Ma. Cette stabilité géodynamique facilite l'interprétation de la dynamique du domaine en érosion en lien avec les déformations épeirogéniques et l'évolution de ces marges. Son contexte climatique, de type essentiellement intertropicale depuis 140 Ma, facilite l'altération et, ainsi, la production de surfaces d'altération (régolithe). Des études récentes ont montré que la corrélation des reliques de surfaces d'altération cénozoïques permet la reconstitution des paleo-drainages et la quantification des volumes érodés à l'échelle sous-continentale [START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF][START_REF] Grimaud | Neogene cratonic erosion fluxes and landform evolution processes from regional regolith mapping (Burkina Faso[END_REF][START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. L'histoire de la dénudation cénozoïque associée est, au premier ordre, en accord avec l'histoire d'accumulation offshore [START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF]Grimaud et al., in prep.;[START_REF] Huyghe | Forçage des liens source-marge au Cénozoïque (marge Bénin-Sénégal[END_REF]. Cependant, seules de très rares reliques de régolithes plus anciennes que le Cénozoïque ont été préservées. A ce jour, l'histoire du relief du craton au Mésozoïque demeure inconnue, ainsi que l'histoire de la dénudation et les quantités de volumes érodés et exportés par le craton. De nouvelles données de la thermochronologie basse-température ont été acquises sur le craton Leo-Man dans le cadre de ce projet afin de révéler l'histoire de la dénudation anté-Cénozoïque.

La marge Atlantique Equatoriale est la zone principale d'accumulation du matériel érodé en Afrique de l'Ouest depuis le Crétacé Inférieur (ca. 140 Ma). L'histoire géodynamique et cinématique de cette marge a été largement discutée dans la littérature [START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF][START_REF] Basile | Geodynamic evolution of the Cote d'Ivoire-Ghana transform margin; an overview of Leg 159 results[END_REF][START_REF] Basile | Erosion and flexural uplift along transform faults[END_REF][START_REF] Antobreh | Rift-shear architecture and tectonic development of the Ghana margin deduced from multichannel seismic reflection and potential field data[END_REF][START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF][START_REF] Heine | Kinematics of the South Atlantic rift: Solid Earth[END_REF]. Elle est découpée en segments par de grandes failles transformantes et a subi une histoire d'extension polyphasée. On s'attend ainsi à une histoire des mouvements verticaux complexe selon le type de segment considéré, chacun ayant une histoire de subsidence et de soulèvement propre. Afin de comprendre l'histoire Mésozoïque du remplissage des bassins INTRODUCTION 16 L'objectif de ce travail est d'étudier, d'une part, l'évolution de la marge Atlantique Equatoriale, notamment l'architecture stratigraphique et les volumes préservés pendant la phase post-rift du Crétacé Supérieur, et d'autre part, l'histoire de la dénudation de l'Afrique de l'Ouest depuis le début du Mésozoïque. Ces résultats permettront de répondre à deux questions majeures: quels sont, d'un point de vue des transferts sédimentaires, les liens terre-mer au Mésozoïque le long de la marge Atlantique Equatoriale et, quels types de mouvements verticaux au niveau de la marge peuvent être associés à ces transferts sédimentaires. Pour répondre à ces questions, ce mémoire de thèse présente les résultats de 5 tâches principales :

(1) La reconstruction paléogéographique onshore-offshore de l'Afrique de l'Ouest en intégrant les bassins intracratoniques afin de comprendre l'évolution des domaines en érosion (source) et en sédimentation (sink) depuis le début du Mésozoïque.

(2) La caractérisation de l'architecture stratigraphique syn-à post-rift des différents segments de la marge à partir de données de sub-surface (sismiques et puits).

(3) La quantification des volumes et des taux d'accumulation des sédiments silicoclastiques dans chaque basin en intégrant les incertitudes associées à la méthode de quantification. Cette tâche a été conduite en collaboration avec Artiom LOPAREV dans le cadre de son stage de Master 2 à l'Université de Toulouse.

(4) La répartition des volumes dénudés à terre estimée d'après l'histoire thermique issue d'une étude de thermochronologie basse-température (traces de fission et (U-Th-Sm)/He sur apatite) en collaboration avec l'Université de Glasgow. Les données AHe ont été acquises par David WEBSTER dans le cadre de sa thèse de doctorat à l'Université de Glasgow. L'analyse des traces de fission et la modélisation des chemins Temps/Température ont été réalisées par Mark INTRODUCTION 17 Le manuscrit est organisé en sept chapitres suivant l'ordre des tâches exposées ci-dessus.

Les chapitres 1 et 2 font un bref état des connaissances sur la dynamique des marges passives (notamment les marges transformantes) et de la géologie de l'Afrique de L'Ouest. Le chapitre 3 présente la nouvelle série de reconstructions paléogéographiques et structurales terre-mer de l'Afrique de l'Ouest depuis le début de Mésozoïque. Le chapitre 4 synthétise l'évolution structurale et stratigraphique syn-à post-rift de la marge Atlantique Equatoriale et le chapitre 5 l'histoire de l'accummulation dans ces bassins. L'histoire de la dénudation et l'estimation des volumes érodés sont présentées dans le chapitre 6. Enfin, le chapitre 7 est consacré à la comparaison volumétrique des matériaux érodés et déposés et aux mouvements verticaux associés à ces transferts de matière.

Ce travail a été financé par le groupe pétrolier TOTAL dans le cadre du projet de collaboration avec le CNRS « TS2P » (Transform Source-to-Sink Project). Total R&D Frontier Exploration a également permis l'accès aux données de subsurface. (2) transform or sheared [START_REF] Mascle | Atlantic-type continental margins; distinction of two basic structural types[END_REF][START_REF] Scrutton | Sedimentary basins of continental margins and cratons Observations on the processes of sedimentary basin formation at the margins of Southern Africa[END_REF]. Rifted margins, also called divergent margins, are characterized by an initial opening motion perpendicular to the continental crust. Transform margins are, as a difference, opened by transcurrent movements parallel to the continental crust.

Kinematic models of rifted margins evolved from pure shear (uniform extension, McKenzie, 1978), simple shear [START_REF] Wernicke | Uniform-sense normal simple shear of the continental lithosphere[END_REF], to recent compound depth-dependent extension models (Huismans andBeaumont, 2008, 2014). Depth-dependent extension with different lithospheric rheological properties accounts for various geometries of rifted margins observed around the world (e.g. narrow Newfoundland-Iberia and ultra-wide South Atlantic margins, Huismans andBeaumont, 2008, 2014, Figure 1-1). Narrow margin can be modelled via rheologically coupled lithospheric crust and mantle, generating a narrow necking zone and exhuming mantle after the breakup of the crust (Figure 1-1A). Whereas wide margin can be reproduced with a weak lower crust, resulting a wide necking zone and the breakup of the mantle before that of the curst (Figure 1-1B, [START_REF] Huismans | Rifted continental margins; the case for depth-dependent extension[END_REF]. Some authors defined rifted margins resulting from 'passive' and 'active' rifting [START_REF] Sengör | Relative timing of rifting and volcanism on Earth and its tectonic implications[END_REF][START_REF] Bott | Stress distributions associated with compensated plateau uplift structures with application to the continental splitting mechanism[END_REF][START_REF] Spohn | Convective thinning of the lithosphere: A mechanism for the initiation of continental rifting[END_REF]. Passive rifting results from a lithospheric extension due to horizontal movements of divergent plates, generating a passive upwelling of underlying asthenosphere. Whereas, active rifting is related to the presence of an active mantle plume head, doming up and cracking the overlaying lithosphere. Uplifted areas usually form by isostatic compensation bordering the active rift center (e.g. East African dome).

Transform/sheared margins were first defined by [START_REF] Mascle | Atlantic-type continental margins; distinction of two basic structural types[END_REF] (Figure 1-2A). They were relatively poorly investigated, although they represent 16% of continental margins in cumulative length (Mercier de Lépinay et al., 2016). Transform faults, first identified by [START_REF] Wilson | A New Class of Faults and their Bearing on Continental Drift[END_REF] as one of three major plate boundary types (mid-oceanic ridge and subduction zone), play a major role in transform margin formation, controlling the continental crust stretching during rifting and oceanic CHAPTER 1 :TRANSFORM MARGINS: A SHORT REVIEW 20 crust formation. The resulting continent-ocean transition is often relatively sharp [START_REF] Keen | Crustal anatomy of a transform continental margin[END_REF][START_REF] Sage | Crustal structure of the continent-ocean transition off the Cote d'Ivoire-Ghana transform margin; implications for thermal exchanges across the palaeotransform boundary[END_REF]. Marginal ridges parallel to transform faults have been locally identified although their origin is still debated [START_REF] Mascle | Atlantic-type continental margins; distinction of two basic structural types[END_REF][START_REF] Wagner | No major thermal event on the Mid-Cretaceous Cote d'Ivoire-Ghana transform margin[END_REF][START_REF] Basile | Erosion and flexural uplift along transform faults[END_REF][START_REF] Basile | Transform continental margins; Part 1[END_REF]. Oblique or oblique-shear margins are intermediate case sharing characteristics of both rifted and transform margins. They formed by obliquity between plate motion and margin direction and undergo oblique-shearing. The major difference between transform/oblique margins and rifted margins is the differential timing between breakup and oceanic spreading [START_REF] Turner | Structure and evolution of an obliquely sheared continental margin: Rio Muni[END_REF]Guiraud et al., 2010, Figure 1-2B). Rifted margins experience immediate oceanic opening after breakup, whereas transform and oblique margins may undergo separately the breakup and the oceanic drift as evidenced by discrete breakup and drift unconformities [START_REF] Turner | Structure and evolution of an obliquely sheared continental margin: Rio Muni[END_REF]. The duration between these two depends on the length of the transform/oblique margin segment and the spreading rate [START_REF] Turner | Structure and evolution of an obliquely sheared continental margin: Rio Muni[END_REF]. with rifted margins opening perpendicularly to margin strike [START_REF] Basile | Transform continental margins; Part 1[END_REF]. (B) Model illustrating the development of oblique margins by oblique shearing associated to oblique-slip faults [START_REF] Turner | Structure and evolution of an obliquely sheared continental margin: Rio Muni[END_REF].

CHAPTER 1 :TRANSFORM MARGINS: A SHORT REVIEW 22

Geodynamic Model of Transform Margins

The geodynamic evolution of transform margins were first illustrated in the model of [START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF], based on geometries and opening kinematics. The model suggests three major stages during the development of transform margin, which differs from the two-stage (synrift and post-rift) evolution of rifted margins (Figure 1-3). During the first intra-continental stage (Figure 1-3A), small segments of rifted/divergent margin form by continental crust stretching and tilted rotated blocks form on both sides of the main shear zone. Active transcurrent deformation occurs along future transform margins between stretched and unstretched continental crusts. The sedimentation and the subsidence are probably high [START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF].

The second syn-transform stage begins when the oceanic crust forms along divergent margins ( Mascle and Blarez,1987, Figure 1-3B). Syn-rift continental sedimentation ends, as a postrift breakup unconformity forms along divergent margins. The hot oceanic spreading ridges migrate progressively towards active transform faults. The evolving contact between a hot center and a continental crust could induce thermal exchanges along future transform margins.

The third post-transform stage starts when the oceanic ridges is beyond the transform margin tip and the two plates are no longer connected (Mascle and Blarez, 1987, Figure 1-3C).

Transform faults are then only active between two oceanic crusts. Transform margins are no longer sheared and undergo mainly thermal subsidence.

A specificity of transform margins is the diachronism of margin connection to a stable oceanic crust during the syn-transform stage. In fact, various locations (blue, purple and red stars in Figure 1-4) experience active transform faulting at different times [START_REF] Basile | Transform continental margins; Part 1[END_REF]. The purple star ends its active transform faulting, before the blue and the red stars (Figure 1-4). The red star location experience active transform faulting during the longest duration until the beginning of post-transform stage. A post-transform unconformity may form, due to an uplift following the progressive passage of oceanic ridge, which should be diachronous along transform margins.

Transform margin are usually bordered at their two extremities by divergent margins. Two types of transfer zones (inner and outer corners) can be identified with distinct characteristics (Basile, 2015, Figure 1-4). The inner corner is not affected by active transform faulting, but by transfer structures (e.g. horsetail system). It records only the post-rift breakup unconformity, as the divergent margins. As a difference, the outer corner experiences the longest transform faulting, ending only at the beginning of post-transform stage. Both post-rift and post-transform unconformities could be recorded with a considerable time interval (x 10 myrs). Marginal ridges can be found at outer corner of transform margins.

The model of [START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF] remains the most popular scenario. It accounts for certain features observed on transform margins, such as narrow continent-ocean transition and CHAPTER 1 :TRANSFORM MARGINS: A SHORT REVIEW 24 different morphologies between inner and outer corner. However, the diachronism of the active transform faulting is rarely confirmed along transform margins, as precise dating is absent.

Figure 1-4 Schematic evolution of a transform margin and adjacent divergent margins [START_REF] Basile | Transform continental margins; Part 1[END_REF].

Equatorial Atlantic Transform Margins of West Africa

Margin Segmentation

Transform margins have been studied in the Equatorial Atlantic domain, that results from the transform rifting in the Lower Cretaceous [START_REF] Macgregor | Play fairways of the Gulf of Guinea transform margin[END_REF][START_REF] Basile | Phanerozoic geological evolution of the Equatorial Atlantic domain[END_REF][START_REF] Antobreh | Rift-shear architecture and tectonic development of the Ghana margin deduced from multichannel seismic reflection and potential field data[END_REF]. The West African and Brazilian margins are segmented into both rifted and sheared margins (Figure 1-5). Conjugate transform margin segments can be identified by tracing major oceanic fracture zones, whereas rifted margins are located at the terminations of two major fracture zones.

Ivory Coast-Ghana Transform Margin

The Ivory Coast-Ghana transform margin is the most studied part of the West African margin, partially because of its spectacular marginal plateau and sharp continent-oceanic transition out during 90s for investigating its evolution and associated vertical movements [START_REF] Basile | Pre-cruise and site surveys; a synthesis of marine geological and geophysical data on the Cote d'Ivoire-Ghana transform margin[END_REF][START_REF] Benkhelil | Submersible observations of Cretaceous deformations along the Côte d'Ivoire-Ghana transform margin[END_REF]Guiraud et al., 1997;[START_REF] Lamarche | The Côte d'Ivoire-Ghana transform margin: sedimentary and tectonic structure from multichannel seismic data[END_REF][START_REF] Mascle | Development of a passive transform margin: Côte d'Ivoire-Ghana transform margin -ODP Leg 159 preliminary results[END_REF]Pletsch et al., 2001;[START_REF] Basile | Geodynamic evolution of the Cote d'Ivoire-Ghana transform margin; an overview of Leg 159 results[END_REF]. They showed a thick sedimentary piles was discovered on the northern slope of the Marginal Ridge connecting to the Deep Ivorian Basin (Figure 1-8). A basal Unit A was identified to be the syn-rifting siliciclastic sequence filling half-grabens of probably Early Aptian-Late Albian age (Figure 1-8A, [START_REF] Basile | Pre-cruise and site surveys; a synthesis of marine geological and geophysical data on the Cote d'Ivoire-Ghana transform margin[END_REF][START_REF] Basile | Geodynamic evolution of the Cote d'Ivoire-Ghana transform margin; an overview of Leg 159 results[END_REF]. The associated sedimentary environments vary from

(
intracontinental lacustrine to open marine from Site 960 to Site 962 [START_REF] Basile | Geodynamic evolution of the Cote d'Ivoire-Ghana transform margin; an overview of Leg 159 results[END_REF]). An [START_REF] Basile | Pre-cruise and site surveys; a synthesis of marine geological and geophysical data on the Cote d'Ivoire-Ghana transform margin[END_REF]. [START_REF] Edwards | Synthesis of the crustal structure of the transform continental margin off Ghana, northern Gulf of Guinea[END_REF].

The formation of the Marginal Ridge has been extensively debated since the 1970s [START_REF] Scrutton | Crustal properties across passive margins On sheared passive continental margins[END_REF][START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF][START_REF] Lorenzo | Development of the continent-ocean transform boundary of the southern Exmouth Plateau[END_REF][START_REF] Vagnes | Uplift at thermo-mechanically coupled ocean-continent transforms; modeled at the Senja fracture zone[END_REF][START_REF] Basile | Geodynamic evolution of the Cote d'Ivoire-Ghana transform margin; an overview of Leg 159 results[END_REF][START_REF] Sage | Crustal structure of the continent-ocean transition off the Cote d'Ivoire-Ghana transform margin; implications for thermal exchanges across the palaeotransform boundary[END_REF][START_REF] Wagner | No major thermal event on the Mid-Cretaceous Cote d'Ivoire-Ghana transform margin[END_REF][START_REF] Basile | Erosion and flexural uplift along transform faults[END_REF][START_REF] Attoh | Seismic stratigraphic record of transpression and uplift on the Romanche transform margin[END_REF][START_REF] Bigot-Cormier | Denudation of the Côte d'Ivoire-Ghana transform continental margin from apatite fission tracks[END_REF]. Various hypotheses were proposed, including crustal thickening by transpression (Figure 1 [START_REF] Basile | Erosion and flexural uplift along transform faults[END_REF]. However, CHAPTER 1 :TRANSFORM MARGINS: A SHORT REVIEW 29 these models are inconsistent with the flat and horizontal Moho below the Marginal Ridge [START_REF] Edwards | Synthesis of the crustal structure of the transform continental margin off Ghana, northern Gulf of Guinea[END_REF][START_REF] Sage | Crustal structure of the continent-ocean transition off the Cote d'Ivoire-Ghana transform margin; implications for thermal exchanges across the palaeotransform boundary[END_REF]. Another discussed model explains the development of the Marginal Ridge by thermal uplift, in which uplift is triggered by heat transfer from the hot oceanic to the continental lithosphere (Figure 1-9E, [START_REF] Scrutton | Crustal properties across passive margins On sheared passive continental margins[END_REF][START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF][START_REF] Vagnes | Uplift at thermo-mechanically coupled ocean-continent transforms; modeled at the Senja fracture zone[END_REF]. It cannot, however, account for the maintenance of the Marginal Ridge long time after the passage of the oceanic ridge. Moreover, the timing of the uplift was revealed to start during the intra-continental stage [START_REF] Basile | Geodynamic evolution of the Cote d'Ivoire-Ghana transform margin; an overview of Leg 159 results[END_REF]. [START_REF] Le Pichon | Marginal offsets, fracture zones, and the early opening of the South Atlantic[END_REF][START_REF] Gorini | The tectonic fabric of the Equatorial Atlantic and adjoining continental marginsௗ: Gulf of Guinea to northeastern Brazil. Projecto Remac-Reconhecimento global da margem continental brasileira, in Estruturas e tectonismo da margem continental brasileira, e suas implicacoes nos processos sedimentares e na avaliacao do potencial de recursos minerais[END_REF][START_REF] Mercier De Lépinay | Iinventaire mondial des marges transformantes et évolution tectosédimentaire des plateaux de Demerara et de Guinée[END_REF]. The evolution of the margin geometry from the syn-to post-rift needs to be further investigated. The post-rift stratigraphic architectures along different margin segments remain unexplored, neither their implication for the margin segmentation.

CHAPTER 2 : CONTEXTE GEOLOGIQUE DE L'AFRIQUE DE L'OUEST

Topographie et Bathymétrie

Figure 2-1 Carte topographique du continent africain (gauche), diagramme de la distribution des altitudes du continent africain (en bas à gauche) [START_REF] Dauteuil | Visages du continent africain -Eléments de géologie africaine[END_REF] et carte morphologique et structurale schématique de l'Afrique (droite) [START_REF] Summerfield | Plate tectonics and the evolution of the African landscape[END_REF].

A la différence des autres continents, l'Afrique possède une hyopsométrie bimodale au premier ordre qui existerait déjà au pré-Crétacé (Figure 2-1): l'altitude moyenne est plus élevée au Sud (Plateau Sud-Africain) et à l'Est (Rift Est Africain) (>1000m) qu'au centre et à l'Ouest (< 500 m) [START_REF] Summerfield | Tectonics, geology and long-term landscape development[END_REF][START_REF] Doucouré | Réalité des communications marines transsahariennes entre la Téthys et l'Atlantique durant le Crétacé supérieur[END_REF].

Des structures topographiques sont superposées: les rides et les bassins (« basins and swells ») et les rifts (Figure 2-1). Le plateau sud-africain et le rift est-africain qui culminent à plus de 1000m forment un Superswell [START_REF] Summerfield | Tectonics, geology and long-term landscape development[END_REF]. Il correspond au système de rifts estafricain se prolongeant par la haute topographie du plateau sud-africain (Figure 2 [START_REF] Summerfield | Tectonics, geology and long-term landscape development[END_REF][START_REF] Doucouré | Réalité des communications marines transsahariennes entre la Téthys et l'Atlantique durant le Crétacé supérieur[END_REF]. L'alternance de bassins et de rides serait liée aux mouvements épeirogéniques dûs à la dynamique mantellique sous la plaque (Figure 2-1) [START_REF] Sahagian | EPeirogenic motions of Africa as inferred from Cretaceous shoreline deposits[END_REF][START_REF] Fairhead | Mesozoic plate tectonic reconstructions of the central South Atlantic Ocean: The role of the West and Central African rift system[END_REF][START_REF] Burke | The African Plate[END_REF][START_REF] Doucouré | Réalité des communications marines transsahariennes entre la Téthys et l'Atlantique durant le Crétacé supérieur[END_REF]. La formation des massifs de point chaud du Nord et du centre de l'Afrique seraient liée à un grand épisode de volcanisme ayant démarré à l'échelle de la plaque vers 35 Ma (Rougier, 2012). [START_REF] Burke | The African Plate[END_REF]Rougier, 2012).

L'hypsométrie de l'Afrique de l'Ouest est aussi bimodale avec un pic proche de zéro et un autre à 300 m [START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF]. Le fait que l'altitude de 300 m soit plus dominante que le niveau de base actuel (0 m) suggère un soulèvement de l'Afrique de l'Ouest de 300 m qui s'est produit durant le Cénozoïque et qui serait encore en cours [START_REF] Bond | Evidence for Late Tertiary Uplift of Africa Relative to North America, South America, Australia and Europe[END_REF][START_REF] Burke | The African Plate[END_REF]. Le mécanisme du soulèvement serait lié à des processus mantelliques profonds consécutifs à un ralentissement de la dérive de la plaque à partir de l'Oligocène (modèle défendu par [START_REF] Burke | The African Plate[END_REF].

Géologie Continentale et Géodynamique

Aperçu des Grands Ensembles Structuraux

Figure 2-3 Carte géologique simplifiée de l'Afrique [START_REF] Dauteuil | Visages du continent africain -Eléments de géologie africaine[END_REF].

Le continent africain offre l'opportunité d'étudier l'histoire de la Terre depuis l'Archéen. ESI : Eastern Senegal inlier, KI : Kayes inlier, BF : Burkina Faso, Tam : Tamanrasset [START_REF] Roussel | Geophysics and the Crustal Structure of West Africa[END_REF].

Les affleurements

On distingue deux grands ensembles précambriens au sein du craton:

x L'Archéen sur la partie Ouest de la dorsale de Léo-Mann et la partie Sud-Ouest de la dorsale Réguibat composées de séries gneissiques et migmatitiques appelées TTG (tonalites, trondhjemites, granodiorites) séparées par des ceintures de roches vertes et intrudées par des plutons [START_REF] Dauteuil | Visages du continent africain -Eléments de géologie africaine[END_REF].

x Le Paléoprotérozoïque occupe la partie Est de la dorsale de Léo-Man et la partie Nord-Est de la dorsale Réguibat. Il est constitué de terrains à granites et ceintures des roches vertes mis en place à partir de ~2000 Ma et affectés par l'orogenèse éburnéenne jusqu'à ~1800 Ma. A la fin de cette orogenèse, le craton est stabilisé.

Figure 2-6 Reconstitution de la bordure NW du continent de Gondwana à la fin du Paléozoïque [START_REF] Villeneuve | Corrélations et évolution des bassins sédimentaires de la marge NW du continent de Gondwana au cours du Paléozoïque inférieur (de la Mauritanie au Vénézuela[END_REF].

Le craton Ouest Africain était connecté avec le craton de Sao Luis au NE du Brésil, selon leur position voisine pré-ouverture de l'Atlantique Equatorial (Figure 2-6, Bertrand et Jardim de [START_REF] Bertrand | Where are the Eburnian-Transamazonian collisional belts[END_REF][START_REF] Villeneuve | Structure, evolution and palaeogeography of the West African craton and bordering belts during the Neoproterozoic[END_REF][START_REF] De Castro | Crustal structure beneath the Paleozoic Parnaíba Basin revealed by airborne gravity and magnetic data[END_REF]. Des chaînes Panafricaines et Hercyniennes entourent le craton Ouest Africain et se prolongent autour du craton de Sao Luis.

Ces orogenèses induisent un fort héritage sur l'évolution Phanérozoïque de l'Afrique de l'Ouest.

Bassins Continentaux de l'Afrique de l'Ouest

Paléozoïque :

Le bassin intracratonique de Taoudeni a accumulé plus de 3 km de dépôts néoprotérozoïque-paléozoïques (Figure 234567). Ils sont couverts au centre par une fine couche de sédiments méso-cénozoïques de moins d'1 km qui contiennent des conglomérats et une série d'alternances argilo-gréso-carbonatées du 'Continental Intercalaire' représentant le Crétacé Inférieur [START_REF] Bellion | Histoire géodynamique post-paléozoïque de l'Afrique de l'Ouest d'après l'étude de quelques bassins sédimentaires[END_REF]. Cénozoïque (Rougier, 2012;Rougier et al., 2013). La formation de ces bassins est associée à la plateforme d'âge Cambrien moyen-Dévonien couvrant l'Afrique septentrionale. Elle est affectée par les cycles de transgression-regression paléozoïques. L'orogenèse hercynienne au Carbonifère-Permien a fait émerger les bassins en formant des chaînes sur la bordure Est de l'Afrique de l'Ouest [START_REF] Guiraud | Phanerozoic geological evolution of Northern and Central Africa: An overview[END_REF].

Les

Le bassin de

L'environnement de dépôt devient continental au Trias-Crétacé Inférieur ('Continental Intercalaire') dans le bassin de Taoudeni et dans les bassins autour du Hoggar.

Mésozoïque :

Un important réseau de rifts s'est développé dans la partie orientale de l'Afrique de l'Ouest à partir du Crétacé Inférieur. Ce système, en forme de 'U', est constitué de plusieurs branches (Figure 2-7):

x La branche SE-NW passant par la Bénoué jusqu'à la Centrafrique;

x La première branche NW-SE dans le bassin du Chad couverte par-dessus des sédiments

Tertiaires. Sa structure est dévoilée à l'aide des données sismiques (Genik, 1993);

x La seconde branche NW-SE parallèle à l'Ouest comprend le bassin de Bida et le fossé de Gao. A l'Ouest du fossé de Gao et dans le centre du bassin de Taoudeni, se trouve un rift E-W d'âge discutable (Jurassique ou Crétacé), appelé le fossé de Nara (Bellion, 1987, Figure 2-7).

Des bassins côtiers se trouvent le long de la marge ouest-africain. Le bassin Sénégalo-Mauritanien est le plus grand d'entre eux avec plus de 10 km de dépôts méso-cénozoïques (Figure 234567). Les bassins côtiers situés en Côte d'Ivoire et au Golfe de Guinée ont une subsidence plus modérée dont la structure et la géométrie seraient associées aux mouvements des grandes failles transformante de l'Atlantique Equatorial [START_REF] Choubert | [END_REF].

Figure 2-7 Carte simplifiée des bassins ouest africains basée sur la carte tectonique de l'Afrique [START_REF] Milesi | Tectonic Map of Africa[END_REF].

Noter que la couverture Méso-Cénozoïque ou Cénozoïque de moins d'1 km d'épaisseur est enlevée de la carte.

Evolution Géodynamique Méso-Cenozoïque de l'Afrique de l'Ouest

Riftings Mésozoïques

Trias-Jurassique :

La dislocation de la Pangée commence au Trias Supérieur (vers 225 Ma) par le rifting de l'Atlantique Central [START_REF] Davison | Central Atlantic margin basins of North West Africa: Geology and hydrocarbon potential (Morocco to Guinea)[END_REF]. De nombreux bassins de rift apparaissent le long de la côte Est de l'Amérique du Nord et la côte Ouest de l'Afrique septentrionale (Figure 2345678). L'axe du rifting est parallèle à la ceinture orogénique hercynienne et contrôlé par des structures préexistantes. [START_REF] Olsen | Stratigraphic record of the early Mesozoic breakup of Pangea in the Laurasia-Gondwana rift system[END_REF].

Selon des données sismiques, de puits et de dykes, l'évolution de l'Atlantique Central est polyphasée [START_REF] Withjack | Diachronous Rifting, Drifting, and Inversion on the Passive Margin of Central Eastern North America: An Analog for Other Passive Margins[END_REF] :

x x L'expansion de la croûte océanique migre du sud au nord jusqu'à l'actuel (Figure 2-9C). [START_REF] Withjack | Diachronous Rifting, Drifting, and Inversion on the Passive Margin of Central Eastern North America: An Analog for Other Passive Margins[END_REF]. Genik, 1992 ;[START_REF] Guiraud | Phanerozoic geological evolution of Northern and Central Africa: An overview[END_REF].

Il s'agit en effet d'un rifting Crétacé polyphasé à l'échelle continentale sur des zones de faiblesse panafricaines. La direction des failles normales est contrôlée par des structures préexistantes panafricaines. Selon [START_REF] Guiraud | Phanerozoic geological evolution of Northern and Central Africa: An overview[END_REF], il existerait deux phases:

x La première phase serait liée à une direction d'extension N160E à N-S (Figure 2 x les rifts orientés NW-SE au Niger et au Chad (le bassin de Termit, Tefidet, Ténéré, Grein, Kfra et N'Dgel Edgi ; West Africain Subsystem (WAS) de Genik, 1993),

x les rifts orientés E-W en Centrafrique (bassins de Bongor, Doba, Doseo et Salamat ;

Central Africain Subsystem (CAS) de Genik, 1993),

x les rifts au Nigéria et au Mali (fossés de la Bénoué, de Gao, bassin de Bida et probable fossé de Nara). Les bassins des deux premiers sous-systèmes (WAS et CAS) sont couverts actuellement par des sédiments cénozoïques. Des études détaillées de ces bassins ont été effectuées à l'aide de données de forage et de sismique par Genik (1993). Des blocs basculés et des failles normales sont observables dans les bassins du WAS, alors que des structures en fleur dans les bassins du CAS suggèrent une déformation transtensive (Genik, 1992 ;Genik, 1993). La phase majeure d'extension dans ces bassins datée du Néocomien-Aptien est suivie par une phase de subsidence thermique (Sag basin) à l'Albien (Figure 2-13). Une réactivation en extension est observée dans le WAS et CAS au moment de la transgression marine cénomanienne suivie par une autre longue phase de subsidence tectono-termique au Turonien-Mid-Maastritchiten. Une inversion tectonique, associée à une direction de raccourcissement NNW-SSE a eu lieu au Santonien (84 Ma). Cette inversion est due au changement de direction et de vitesse de mouvement de plaque Africaine associé à la convergence entre l'Europe et l'Afrique [START_REF] Guiraud | Senonian basin inversion and rejuvenation of rifting in Africa and Arabia; synthesis and implications to plate-scale tectonics[END_REF]. Cette inversion se manifeste par des structures réactivées en compression et en transpression observées dans le WAS et CAS, notamment dans le fossé de la Bénoué, le bassin de Bongor, Doseo et Doba (Genik, 1993;[START_REF] Cooper | The geometric characteristics, genesis and petroleum significance of inversion structures[END_REF]. Des plis et des structures en fleur en transpression dextre sont également observés dans le fossé de la Bénoué et les bassins soudanais (Figure 2-10, Guiraud et Bosworth, 1997). Une dernière réactivation en extension a eu lieu au Mid-Maastrichtien-Paléogène dans le WAS. Elle s'est terminée par de nouveau une phase de subsidence thermique (Figure 2-13) (Genik, 1993).

Figure 2-12 Schéma structural de la partie occidentale des WCARS (Genik,1992).

En comparant les résultats de Genik (1993) avec le modèle de Guiraud et al. (2005), on constate des désaccords notamment sur les âges de syn-rift. En effet, selon Genik (1993), il y n'a pas eu de déformation extensive à l'Albien dans les bassins de WAS et CAS contrairement à ce que suggère le modèke de Guiraud et al., (2005). La deuxième phase de syn-rift de Guraud et al.

(2005) correspondrait à la réactivation au Cénomanien dans le modèle de Genik (1993). La troisième phase d'extension au Mid-Maastrichtien-Paléogène dans des rifts du WAS n'a pas été prise en compte par [START_REF] Guiraud | Phanerozoic geological evolution of Northern and Central Africa: An overview[END_REF]. Afin de mieux comprendre l'évolution du WCARS, l'étude tectono-sédimentaire des bassins de rift au Nigéria et au Mali (fossé de la Bénoué, bassin de Bida, etc., Figure 2-12) sera nécessaire.

Figure 2-13 Evolution paléotectonique des bassins de rift de la partie occidentale du WCARS. A noter que les âges absolus sont à réactualiser (Genik, 1993).

Evolution Cénozoïque

Le WCARS continue d'évoluer au Cénozoïque. Une phase de rifting est enregistrée dans les bassins du WAS au Maastrichtien Supérieur-Eocène Inférieur qui est suivie par une période de subsidence thermique (Sag) et de chute eustatique à l'Eocène-Oligocène (Figure 2-13, Genik, 1993). Cependant, les bassins du CAS présentent des alternances de subsidence et soulèvement au Cénozoïque.

A l'Est, un grand épisode de rifting a commencé à l'Oligocène Supérieur (30 Ma) en Afrique de l'Est, dans la mer Rouge et dans le golfe d'Aden . Le processus est considéré comme étant l'origine du futur rift est-africain.

La collision entre l'Afrique et l'Europe a débuté à l'Eocène Supérieur (37 Ma) avec une direction de compression N160, au même moment que le ralentissement de la plaque africaine [START_REF] Burke | The African Plate[END_REF][START_REF] Guiraud | Phanerozoic geological evolution of Northern and Central Africa: An overview[END_REF]. Elle a ensuite été intensifiée au Miocène (22 Ma) en formant la chaîne Atlas-Alpine au Nord-Ouest de l'Afrique. La répercussion de la collision alpine sur l'Afrique de l'Ouest reste très mal contrainte. Des linéaments seraient réactivés, y compris le linéament guinéo-nubien E-W, panafricain N-S, etc. (Figure 2-14, [START_REF] Guiraud | Les linéaments guinéo-nubiensௗ: un trait structural majeur à l'échelle de la plaque africaine[END_REF][START_REF] Guiraud | Tectonique, Seismicité et volcanisme de la plaque africaine depuis le Méso-Cénozoïque[END_REF]. Cependant, on observe rarement sur ces linéaments une déformation ou des décallages contemporains qui soient clairement démontrés.

Des bombements topographiques (le Hoggar, l'Aïr, l'Iforas, le Tibesti, etc.) se sont formés en association avec un grand épisode de volcanisme en Afrique depuis 35 Ma (Figure 2-1 et Figure Rougier, 2012). Des bourrelets marginaux le long l'Océan Altantique (guinéen, namibien, etc) se sont développés (Figure 2-14). Le taux de dénudation le plus élevé a été localisé sur le bourrelet marginal guinéen au cours du Cénozoïque [START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF]. Il s'agit en effet de mouvements verticaux de grandes longueurs d'onde et d'amplitudes variables à l'échelle continentale qui ne sont pas encore bien caractérisés en terme de quantité de soulèvement, d'origines (mouvement mantellique, collision alphine, etc), et quant aux effets de l'héritage des anciennes structures. Selon [START_REF] Burke | The African Plate[END_REF], les mouvements verticaux sont dus aux processus mantelliques associés au ralentissement du mouvement de la plaque africaine depuis l'Oligocène.

2-14,

Magmatisme Post-Paléozoïque

Même si la région est considérée comme 'stable' depuis la fin du Paléozoïque, une activité magmatique non négligeable est documentée en Afrique de l'Ouest. Ses relations avec la tectonique et/ou les mouvements verticaux de la sous-région sont encore mal définies. La Figure 2-15 montre la répartition du magmatisme en Afrique de l'Ouest depuis le Trias :

x Les coulées, dykes et sills doléritiques de la province magmatique de l'Atlantique

Central (Central Atlantic Magmatic Province (CAMP), 200 Ma) sur la partie occidentale du craton et dans le bassin de Taoudenni.

x Des kimberlites du Crétacé Inférieur, réparties sur la partie occidentale du craton,

x Des complexes granitiques alcalins jurassiques (213-140 Ma) sur le plateau de Jos (Younger Granites, Figure 2-2),

x Le magmatisme Crétacé-Eocène Inférieur dans le fossé de la Bénoué,

x Des complexes granitiques alcalins plus récents le long de la ligne volcanique du Cameroun et dans le Hoggar,

x Des épanchements basaltiques cénozoïques sur le socle panafricain du bombement du Hoggar (Hoggar proprement dit et Aïr, Figure 2-2),

x La chaîne volcanique du Cameroun au SE du bassin de la Bénoué. x BSMA (Blake Spur Magnetic Anomaly) et ABSMA (African Blake Spur Magnetic Anomaly) datés Bajocien Inférieur (170 Ma) identifiable seulement dans la partie Sud de la côte Atlantique Central coïncident avec le changement de la topographie du socle lié à la vitesse de l'expansion.

Cinématique de l'Atlantique

x Anomalies M0 conjugués daté 120,6 Ma [START_REF] Gaina | The African Plate: A history of oceanic crust accretion and subduction since the Jurassic[END_REF].

x Anomalies M25 conjugués daté 154 M. [START_REF] Schettino | Breakup of Pangaea and plate kinematics of the central Atlantic and Atlas regions[END_REF][START_REF] Labails | An alternative early opening scenario for the Central Atlantic Ocean[END_REF][START_REF] Withjack | Diachronous Rifting, Drifting, and Inversion on the Passive Margin of Central Eastern North America: An Analog for Other Passive Margins[END_REF].

Au Sinémurien Supérieur-Bajocien Inférieur (190-170 Ma), l'accrétion de la croûte océanique était lente (0,8 cm/an) avec probablement une direction d'expansion NNW-SSE oblique par rapport à l'axe (Figure 2 Dans ce modèle cinématique de l'ouverture de l'Atlantique Central, l'accrétion est en fait asymétrique, avec un taux d'accrétion plus grand à l'Ouest qu'à l'Est (Figure 2-18). Cette asymétrie peut-être liée à l'anomalie thermique situé préférentiellement sous la plaque africaine durant la CAMP dont l'éruption violente dans les rifts triasiques se serait propagée très loin vers l'ouest [START_REF] Labails | An alternative early opening scenario for the Central Atlantic Ocean[END_REF]. D'autres modèles de la cinématique proposent une accrétion symétrique impliquant des sauts de ride océanique (Schettino et Turo, 2009). Falklands sert de jonction entre la ride Atlantique et la ride de l'Inde SW [START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF]. Il a eu lieu au Néocomien-Aptien, comme le montre par le développement des bassins offshores au NE du Brésil [START_REF] De Matos | The northeast Brazilian rift system: Tectonics[END_REF]. Le rifting dans le segment central s'est fait en deux phases, du Nord au Sud et du Berriasien Supérieur jusqu'au début de l'Aptien. Il s'est terminé par une phase de subsidence (Sag bassin) au Mid-Aptien-Aptien Supérieur [START_REF] Chaboureau | Paleogeographic evolution of the central segment of the South Atlantic during Early Cretaceous times: Paleotopographic and geodynamic implications[END_REF]. Au même moment, le rifting avorté s'est développé dans le continent Africain avec une phase majeure au

Ouverture de l'Atlantique Sud

Valanginien-Aptien (Genik, 1993) Cependant, dans ces modèles, les limites océan/continent sont déterminées à partir les anomalies magnétiques qui sont parfois absentes, sans tenir compte de la zone de transition O/C qui peut parfois atteindre quelques centaines de km de large (25-700 km). La variation de la position de la ligne de rivage contrôlée par le flux de sédiments au cours du temps géologique peut avoir une influence sur la reconstruction.

Introduction

The Equatorial Atlantic Ocean opened as a consequence of oblique divergence along what were to become the best-known examples of transform / oblique continental margins of Northern South America and West Africa [START_REF] Emery | Continental margin off western Africa; Angola to Sierra Leone[END_REF][START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF][START_REF] Basile | Phanerozoic geological evolution of the Equatorial Atlantic domain[END_REF]; oblique divergence (e.g., [START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF][START_REF] Frizon De Lamotte | Style of rifting and the stages of Pangea breakup[END_REF]. The intracontinental African rifts, which were connected to the South and Equatorial Atlantic rift systems by a triple point, aborted before the African continent could split into three sub-plates along the Western and Central Rift System [START_REF] Burke | Uplift, Rifting and the Break-up of Africa[END_REF]Guiraud and Maurin, 1992, Figure 3-1). Given their transform character, the margins of the Equatorial Atlantic Ocean were mainly investigated through the kinematics of Ocean opening (e.g., [START_REF] Basile | Phanerozoic geological evolution of the Equatorial Atlantic domain[END_REF][START_REF] Heine | Kinematics of the South Atlantic rift: Solid Earth[END_REF][START_REF] Heine | Oblique rifting of the Equatorial Atlantic; why there is no Saharan Atlantic Ocean[END_REF][START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF] with an emphasis on the fracture zones and the vertical movements induced along the margins (Clift et al., 1998;Bouillin et al., 1998;[START_REF] Bigot-Cormier | Denudation of the Côte d'Ivoire-Ghana transform continental margin from apatite fission tracks[END_REF][START_REF] Mercier De Lépinay | Iinventaire mondial des marges transformantes et évolution tectosédimentaire des plateaux de Demerara et de Guinée[END_REF]. The abruptness of the Equatorial margins of Africa results from the strong control of transforms during rifting. These steep margins have specific thermal and subsidence histories that are not yet well understood, but they are crucial in controlling -and for

unraveling -their high hydrocarbon potential [START_REF] Burke | Africa's petroleum systems: four tectonic "Aces" in the past 600 million years[END_REF][START_REF] Macgregor | Play fairways of the Gulf of Guinea transform margin[END_REF].

Published exploration studies have provided insights [START_REF] Delteil | Continental margin in the northern part of the Gulf of Guinea[END_REF][START_REF] Kjemperud | Tectonostratigraphic history of the Keta Basin, Ghana with emphasis on late erosional episodes[END_REF][START_REF] Bennett | Regional 2D seismic interpretation and exploration potential of offshore deepwater Sierra Leone and Liberia[END_REF][START_REF] Macgregor | Play fairways of the Gulf of Guinea transform margin[END_REF], but only at the scale of individual sub-basins and/or along cross sections that do not allow apprehending the fully three-dimensional nature of the tectonostratigraphic evolution of the margins.

Integrated regional studies allowing for linking the stratigraphic history of the margins to their deformation since pre-rift configuration are still lacking. Such studies require structural and paleogeographic reconstitutions (i.e., maps showing depositional environments) of their adjoining continental domain in order to address the coupling between margins evolution and the erosional and deformation history of their hinterland in a "source-to-sink" perspective. So far, paleogeographic reconstitutions for Northwestern Africa did not include the Equatorial margin domain (e.g., [START_REF] Guiraud | Phanerozoic geological evolution of Northern and Central Africa: An overview[END_REF]. Furthermore, those paleogeographic reconstitutions were biased from a methodological viewpoint. Indeed, they consider the preservation limits of sedimentary deposits of a given age as the limits of the sedimentation area of that age. But it is never the case, because the edges of coastal and intracratonic basins undergo erosion that leads to significant reduction of the basins' original extent (e.g., [START_REF] Sloss | Geometry of sedimentary basins; applications to Devonian of North America and Europe[END_REF][START_REF] Watts | Isostasy and Flexure of the Lithosphere[END_REF].

In this contribution, we reassess the Meso-Cenozoic structural, stratigraphic, magmatic and geomorphic evolution of the Equatorial margins of northwestern Africa and their hinterland (south of 28°N, West of 17°E) as well as the conjugate Equatorial margins of Northern South America (2) fault patterns and magmatic occurrences, (3) extent of sedimentation / erosion areas and associated depositional environment of sediments, and (4) constraints provided by low-temperature thermochronology data on the burial / erosion of specific areas. Our work is based on a compilation of original geological source data from the literature, as well as seismic and well data along the continental margins. A specificity of our approach is that we evaluated the potential original minimal extent of sedimentary deposits for coastal and intracratonic basins beyond the present-day erosional limit of those basins. In addition to provide a new evolving integrated structural / sedimentary offshore -onshore scheme at a sub-continental scale, we proposed a new pre-rift fit between South America and Northwestern Africa to account for our observations. Our study opens new perspective for linking margins' evolution to intracontinental long-wavelength deformation and erosion / deposition patterns, with implication for shield-margin source-to-sink systems.

Geological Outline and Earlier Works

The West African lithosphere mainly consists in an Archean-Proterozoic craton, (i. or directly on the basements [START_REF] Radier | Contribution à l'étude géologique du Soudan oriental (AOF). 2 Le bassin crétacé et tertiaire de Gao le détroit soudanais[END_REF][START_REF] Greigert | Description des formations crétacées et tertiaires du bassin des Iullemeden (Afrique occidentale[END_REF][START_REF] Busson | The Sahara from the Middle Jurassic to the Middle Cretaceous: Data on environments and climates based on outcrops in the Algerian Sahara[END_REF][START_REF] Davidson | The structure, stratigraphy and petroleum geology of the Murzuq Basin, Southwest Libya[END_REF]; See also [START_REF] Choubert | International Geological Map of Africa[END_REF][START_REF] Fabre | Evolution des terrains mésocénozoïques d'une marge à l'autre du craton ouest africain, entre le Tanezrouft (Algérie) et l'Adrar de Mauritanie[END_REF]. Jurassic and -mostly -Lower Cretaceous intracratonic sediments have been grouped as the "Continental Intercalaire", which is dated only by sparse vertebrates and fossil woods [START_REF] Dars | Les formations sédimentaires et les dolérites du Soudan occidental (Afrique de l'Ouest)[END_REF]Lefranc, 1983a;[START_REF] Lefranc | The continental intercalaire of northwestern Sahara and its equivalents in the neighbouring regions[END_REF]Mateer et al., 1992, Figure 3-1). A Cretaceous rift system is preserved inland West Africa, most of which is now buried under Upper Cretaceous and Cenozoic series: the Western Central Rift System in the Chad basin, which extends up to East Africa, the Gao and Bida rifts in the Iullemmeden basin, and the Nara and Amded rifts in the Taoudeni basin [START_REF] Radier | Contribution à l'étude géologique du Soudan oriental (AOF). 2 Le bassin crétacé et tertiaire de Gao le détroit soudanais[END_REF][START_REF] Dars | Les formations sédimentaires et les dolérites du Soudan occidental (Afrique de l'Ouest)[END_REF][START_REF] Bellion | Sismicité historique de l'Afrique de l'Ouest. Essai d'inventaire[END_REF][START_REF] Fabre | Evolution des terrains mésocénozoïques d'une marge à l'autre du craton ouest africain, entre le Tanezrouft (Algérie) et l'Adrar de Mauritanie[END_REF]Genik, 1992Genik, , 1993;;[START_REF] Zanguina | An Introduction to the Petroleum Potential of Niger[END_REF]Figure 3-2). The Upper Cretaceous sequences recorded mostly transgressions far inland that ultimately formed the "Trans-Saharan Seaway", connecting the Equatorial Atlantic Ocean to the Tethys Ocean [START_REF] Reyment | Biogeography of the Saharan Cretaceous and Paleocene epicontinental transgressions[END_REF][START_REF] Doucouré | Réalité des communications marines transsahariennes entre la Téthys et l'Atlantique durant le Crétacé supérieur[END_REF]. Marine sedimentation is recorded repeatedly until the Late Paleocene-Early Eocene, particularly in the Iullemmeden and Chad basins by limestone and phosphate deposits (e.g., [START_REF] Radier | Contribution à l'étude géologique du Soudan oriental (AOF). 2 Le bassin crétacé et tertiaire de Gao le détroit soudanais[END_REF][START_REF] Kogbe | The Trans-Saharan Seaway during the Cretaceous[END_REF][START_REF] Reyment | Biogeography of the Saharan Cretaceous and Paleocene epicontinental transgressions[END_REF][START_REF] Moody | The Cretaceous deposits of the Iullemmeden Basin of Niger, central West Africa[END_REF]. Those series are overlain by fluvial sediments of the late Eocene -Oligocene 'Continental

Terminal' [START_REF] Lang | Le Sidérolithique du Tertiaire ouest-africain et le concept de Continental Terminal[END_REF][START_REF] Lang | The continental terminal in West Africa[END_REF][START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]Figure 3-2). Intense weathering has affected West Africa since the Late Cretaceous and left relicts of lateritic paleo-landscapes, which have been used for reconstructing denudation histories and drainage evolution of West Africa [START_REF] Beauvais | Modes, tempo, and spatial variability of Cenozoic cratonic denudation; the West African example[END_REF][START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. The present-day West African drainage system has stabilized since the Early Oligocene, following the onset of hot spot-related growth of intraplate basin-and-swell topography [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF].

The inland rift system is temporally and kinematically linked to the development of the Equatorial Atlantic margin of Africa [START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF][START_REF] Heine | Oblique rifting of the Equatorial Atlantic; why there is no Saharan Atlantic Ocean[END_REF], which may be divided into three segments separated by transforms (the NW trending Guinea-Liberia margin, the E-W trending Ivory Coast and Ghana-Benin margins, Figure 3-1). The current views on the opening of the Equatorial Atlantic Ocean are summarized as follows [START_REF] Popoff | Du Gondwana à l'atlantique sud: les connexions du fossé de la bénoué avec les bassins du Nord-Est brésilien jusqu'à l'ouverture du golfe de Guinée au crétacé inférieur[END_REF]MacGregor et al., 2003;[START_REF] Brownfield | Geology and total petroleum systems of the Gulf of Guinea Province of West Africa[END_REF]. The syn-rift stage begins during the Neocomian by transcurrent and extensional faulting [START_REF] Macgregor | Play fairways of the Gulf of Guinea transform margin[END_REF]Brownfield and Charpentier, 2006, Figure 3-1). Grabens and half-grabens of the Ghana-Benin margin are filled by Barremian -Aptian continental conglomerates, sandstones and siltstones [START_REF] Kjemperud | Tectonostratigraphic history of the Keta Basin, Ghana with emphasis on late erosional episodes[END_REF][START_REF] Chierici | Stratigraphy, palaeoenvironments and geological evolution of the Ivory Coast-Ghana basin[END_REF], which are overlain by Albian marine sandstones, black shales and minor limestones [START_REF] Chierici | Stratigraphy, palaeoenvironments and geological evolution of the Ivory Coast-Ghana basin[END_REF]. The end of syn-rift deformation is marked by a major regional unconformity underlying Latest Albian-Cenomanian marine series, 'the Breakup unconformity', also observed on the conjugate Brazilian margins [START_REF] Zalan | Bacia do Marajo[END_REF][START_REF] Junior | Bacia de Barreirinhas[END_REF][START_REF] Soares Júnior | Evolução do rifteamento e paleogeografia da margem Atlântica Equatorial do Brasil[END_REF]. The kinematic model for the opening of the Equatorial Atlantic Ocean is still debated, because of the 'Cretaceous Magnetic Quiet' period and a lack of strong constraints on syn-rift structures restoration [START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF][START_REF] Heine | Kinematics of the South Atlantic rift: Solid Earth[END_REF]. Regression and transgression cycles and tectonic reactivation affected the African Equatorial Atlantic margin during the post-rift stage. Two major regional unconformities whose origin is debated are identified on the Ivory Coast and Ghana-Benin margins in the Senonian and the Oligocene [START_REF] Simon | La discordance oligocène et les dépôts posterieurs a la discordance dans le bassin sédimentaire ivoirien[END_REF]Grillot et al., CHAPTER 3 :PALEOGEOGRAPHIC AND STRUCTURAL RECONSTRUCTION 70 1985;[START_REF] Chierici | Stratigraphy, palaeoenvironments and geological evolution of the Ivory Coast-Ghana basin[END_REF]. Lateral variations in syn-rift deformation patterns and the correlations within the post-rift stratigraphy along the whole margin are also not well established. Despite some largescale first-order kinematic syntheses such as those of [START_REF] Fairhead | Mesozoic plate tectonic reconstructions of the central South Atlantic Ocean: The role of the West and Central African rift system[END_REF], [START_REF] Binks | A plate tectonic setting for Mesozoic rifts of West and Central Africa[END_REF] or [START_REF] Guiraud | Early Cretaceous rifts of Western and Central Africa: an overview: Tectonophysic[END_REF], no study has integrated the tectonostratigraphic evolution of the margin and that of its hinterland. Terminal", respectively. Only outcropping faults that were potentially activated during the Meso-Cenozoic are shown.

Sources for low-temperature thermochronological data shown on the map are listed in Table 3-1. The Equatorial Atlantic Ocean is classically the oceanic lithosphere between the Guinea Fracture Zone to the North (boundary with the Central Atlantic Ocean) and the Chain Fracture Zone in the South (boundary with the South Atlantic Ocean). FZ:

Fracture Zone.

Materials and Method

We established four large-scale onshore-offshore cross-sections across the study area in order to visualize the spatial relationships among inland sedimentary basins and continental margins, and particularly the marginal upwarp separating these two domains (Figure 3-3). These cross-sections complement the paleo-maps, which were established for specific periods matching known geodynamic episodes such as the emplacement of magmatic provinces, the continental rifting or global transgression/regression. Paleo-maps represent time increments usually less than 10 Myr. In this study, we refer to the time scale of Walker et al. (2012).

Integration of the Sedimentary Record

The paleo-maps display the depositional environments and potential extent of intracontinental and marginal basins. We first mapped the boundaries of the preserved sediments deposited during each time step. Stratigraphy, lithology and paleoenvironment of these deposits (both at the surface and subsurface) have been compiled from published literature reporting firsthand data, observations and maps (Table 3-1). Additional information was obtained along the African Equatorial Atlantic margins and in the Gao rift on the basis of seismic and well data. For

South American basins, we used essentially published sedimentological studies and detailed stratigraphic charts of Petrobras [START_REF] Figueiredo | Bacia da Foz do Amazonas[END_REF][START_REF] Zalan | Bacias de Braganca-Viseu[END_REF][START_REF] Zalan | Bacia do Marajo[END_REF][START_REF] Junior | Bacia de Barreirinhas[END_REF][START_REF] Neto | Bacia Potiguar[END_REF][START_REF] Conde | [END_REF]. Depositional environments of sediments are grouped in four categories: non-marine/continental, transitional, shallow marine and deep marine. Transitional environment are coastal, lagoonal, estuary and/or deltaic sedimentary environments with near sea level elevation. Available paleocurrent measurements are also indicated. The present-day extent of preserved sedimentary deposits is hypothetical when strata are covered by younger deposits and are only revealed by seismic and well data. For non-marine deposits, in particular, the 'Continental Intercalaire' that are usually poorly dated, only uncertain (dashed) boundaries have been represented. At the edges of intracratonic and coastal basins, the present-day map sedimentary limits of a given age are usually erosional limits. Indeed, erosion generally removes deposits along basin's fringes as a consequence of flexural uplift of basins' edges accompanying subsidence and sediment accumulation [START_REF] Sloss | Sequences in the Cratonic Interior of North America[END_REF][START_REF] Sloss | Geometry of sedimentary basins; applications to Devonian of North America and Europe[END_REF]Watts, 2001, Figure 3-4A). The preserved deposits therefore only represent the minimum extent of the deposits at the time they emplaced.

This has led to major methodological limitation of paleogeographic studies, which usually mistake the extent of preserved sediments for their depositional area. In this study, we have assessed the For non-marine deposits, ǻZ may be constrained from basement denudation estimates derived from geomorphology and low-temperature thermochronology. For instance, denudation of the Leo-Man Shield (Figure 3-1 and Figure 3-2) is estimated to be in the range of 2 to15 m/Ma for the Cenozoic, based on incision of dated lateritic relict landscapes [START_REF] Beauvais | Modes, tempo, and spatial variability of Cenozoic cratonic denudation; the West African example[END_REF][START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF][START_REF] Grimaud | Neogene cratonic erosion fluxes and landform evolution processes from regional regolith mapping (Burkina Faso[END_REF] and 6 -13 m/Ma for the Mesozoic based on low-temperature thermochronological analysis (Gunnell, 2003). Assuming an average denudation rate of 9 m/Ma in the past over a 10 Myr period (typical time-slice of successive paleo-maps), the value of E would be 300 to 900 km for intracratonic basins (considering Si = 0.1 to 0. To summarize, the potential miminum original horizontal extent of sedimentary basins' edges in the past is of the order of 100 km (typically 300 km) greater than that of preserved deposits in intracratonic contexts. This value would be of the order of tens of kilometers (typically 50 km) for coastal basins. On must point out that this approach does not apply to active rifts sedimentation, which is mostly controlled by active faults bounding the deposits [START_REF] Magnavita | Rifting, erosion, and uplift history of the Reconcavo-Tucano-Jatoba Rift[END_REF].

Paleocurrent data have locally been used to further constrain the potential minimum original extent of sedimentation areas, because they help reconstructing paleo-alluvial plains later fragmented by uneven erosion. If paleocurrents indicate flow towards a present-day exposed basement, the basement had to be flooded by the considered alluvial plain when the plain was active.

Published apatite fission track analysis (AFTA) and apatite (U-Th-Sm)/He dating have also been used to further constrain the extent of past depositional areas, as they constrain thermal histories of samples residing in the first 3-4 km of the crust (e.g., [START_REF] Gallagher | Fission track analysis and its applications to geological problems[END_REF][START_REF] Ehlers | Apatite (U-Th)/He thermochronometry; methods and applications to problems in tectonic and surface processes[END_REF]. Considering the non-orogenic context of West Africa and its margins, and in the cases where the samples were not affected by thermal events such as magmatism, heating periods

Fault Patterns

Intracontinental active faults were mainly established from literature sources (Table 3-1).

For the Equatorial Atlantic margins, we also integrated results of our interpretation of unpublished seismic profiles calibrated by boreholes on the African side, and used published fault patterns for the South American side (Table 3-1

Magmatism

We compiled and mapped the location, emplacement mode, age and dating method of Meso-Cenozoic magmatic occurrences in West Africa and along its margins from literature (Figure 3-5 to Figure 3-13; Appendix 1). For northern South America, we used the synthesis of [START_REF] Mizusaki | Mesozoic and Cenozoic igneous activity and its tectonic control in northeastern Brazil[END_REF]. Magmatic occurrences are categorized in lava flow, dyke/sill, ring complex, kimberlite clusters and kimberlite occurrences (

Palinspastic and Kinematic Reconstruction

We adopted the kinematic models of the Atlantic Ocean opening proposed by [START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF] and [START_REF] Heine | Kinematics of the South Atlantic rift: Solid Earth[END_REF] for relatively positioning the current coastlines for each time slice.

The pre-rift and pre-opening fits between West Africa and northern South America proposed by (2013) appears to be more consistent with our syn-rift fault patterns on conjugate margins (see below), which must develop within stretched and thinned continental crusts, assuming no major post-rift reactivation occurred. It also appears to better match what is known from the timing of the lithospheric breakup [START_REF] Dumestre | The petroleum geology of the Republic of Guinea Bissau[END_REF][START_REF] Kjemperud | Tectonostratigraphic history of the Keta Basin, Ghana with emphasis on late erosional episodes[END_REF][START_REF] Chierici | Stratigraphy, palaeoenvironments and geological evolution of the Ivory Coast-Ghana basin[END_REF]. We therefore used the kinematic model of [START_REF] Heine | Kinematics of the South Atlantic rift: Solid Earth[END_REF] from the Valanginian to the Late Albian, and adjusted it based on our mapping of fault patterns. As for the post-rift period, we adopted the model of [START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF] because the magnetic anomalies they used are well constrained from 84 Ma onward (Chron 34).

We produced nine paleo-maps for Late Triassic-Early Jurassic (235-190 Ma, Figure 3

Results and Interpretation

Cross-sections Linking the Marginal and Intracontinental Domain

The cross-sections display the present-day configurations of onshore and offshore basins, basement highs and their typical wavelengths (Figure 3-3). The geometry is spatially consistent across the Central and Equatorial margins, with continental margin basins separated from intracratonic basins by a marginal upwarp (or bulge). The inland basal unconformities of intracratonic basins coincide with the slope of basement highs such as the Hoggar and Reguibat shields. The marginal upwarps are long-wavelength positive topographic features that are believed to form at the time of rifting and are sustained and/or reactivated afterwards [START_REF] Gilchrist | Differential denudation and flexural isostasy in formation of rifted-margin upwarps[END_REF][START_REF] Gallagher | Denudation, fission track analysis and the long-term evolution of passive margin topography: application to the southeast Brazilian margin[END_REF]. Considering only the Meso-Cenozoic sediments (that recorded continental surface evolution of northwestern Africa since the rifting of the Central Atlantic), the edges of intracratonic basins are erosional limits, resulting from the truncation of the strata on the inland slopes of the marginal upwarps. Similar truncations are expected, though on a shorter wavelength, at the coastal fringes of marginal basins (see also Figure 3-3B) and along the edges of intracratonic basins on the slopes of intracratonic highs.

Our cross-sections show that the preservation patterns of sediments in intracratonic basins at a sub-continental scale is controlled by an interference in time and space, between intracontinental basement highs and marginal upwarps that have contrasted wavelengths, notwithstanding intracratonic basins subsidence histories. Furthermore, Meso-Cenozoic basins display uneven spatial relationships with preserved Neoproterozoic and Paleozoic depocenters. During the Late Triassic -Earliest Jurassic, multiple rifts form from North to South along the future Central Atlantic margins and inland North America (e.g., Labail et al., 2010). Nonmarine sediments and massive salt deposits accumulate and are preserved today in these rift basins [START_REF] Olsen | Stratigraphic record of the early Mesozoic breakup of Pangea in the Laurasia-Gondwana rift system[END_REF][START_REF] Brownfield | Assessment of the undiscovered oil and gas of the Senegal Province, Mauritania, Senegal, the Gambia, and Guinea-Bissau[END_REF][START_REF] Davison | Central Atlantic margin basins of North West Africa: Geology and hydrocarbon potential (Morocco to Guinea)[END_REF]. The extent of these deposits may have been much wider originally given the pervasive unconformity truncating the upper syn-rift sediments [START_REF] Olsen | Stratigraphic record of the early Mesozoic breakup of Pangea in the Laurasia-Gondwana rift system[END_REF][START_REF] Withjack | Diachronous Rifting, Drifting, and Inversion on the Passive Margin of Central Eastern North America: An Analog for Other Passive Margins[END_REF]. The Guinea-Liberia margin seems to experience crustal stretching at this time, given the accumulations of aeolian sediments interbedded with basaltic lava flows reported in South America [START_REF] Figueiredo | Bacia da Foz do Amazonas[END_REF][START_REF] Soares Júnior | Evolução do rifteamento e paleogeografia da margem Atlântica Equatorial do Brasil[END_REF].

This, together with our observations on unpublished seismic lines, suggests the occurrence of an aborted Central Atlantic rift along the future Guinea-Liberia margins of the Equatorial Atlantic. In the continent, non-marine sediments (mainly siltstones) are deposited in the north-easternmost part of the study area (future Iullemmeden, Murzuk and Chad basins) with currents to the N or NW As North America has been drifting away from West Africa since the Early Jurassic, the Central Atlantic margin of Africa had long reached its post-rift stage and builds a continental shelf [START_REF] Dillon | The development of the continental margin of eastern North America-conjugate continental margin to West Africa[END_REF][START_REF] Davison | Central Atlantic margin basins of North West Africa: Geology and hydrocarbon potential (Morocco to Guinea)[END_REF][START_REF] Baby | Vertical movements in NW Africa margin: controls on accomodation and sedimentary partionning[END_REF]. Rifting takes place along the future Guinea Plateau (Figure 3-2) and its South American counterpart (the Demerara plateau), where

Valanginian syn-rift sediments have been reported [START_REF] Gouyet | Evolution tectono-sédimentaire des marges guyanaise et nord-brésilienne au cours de l[END_REF]. That rifting probably propagated along the future Guinea-Liberia margin into the interior of South America (Cassipore and Marajo graben; [START_REF] Figueiredo | Bacia da Foz do Amazonas[END_REF][START_REF] Zalan | Bacia do Marajo[END_REF]. The NE-SW trending Tacutu rift (onshore Suriname, further to the West) continues to be filled after its initiation in the Late Jurassic (Vaz et al., 2007b). The future South Atlantic domain consists in a wide rift system receiving non-marine sediments [START_REF] De Matos | The northeast Brazilian rift system: Tectonics[END_REF][START_REF] Chaboureau | Paleogeographic evolution of the central segment of the South Atlantic during Early Cretaceous times: Paleotopographic and geodynamic implications[END_REF]. It is mostly located in intracontinental South America and interacts with ENE-trending transfer faults (future transforms)

reactivating Panafrican shear zones (e.g., [START_REF] Popoff | Du Gondwana à l'atlantique sud: les connexions du fossé de la bénoué avec les bassins du Nord-Est brésilien jusqu'à l'ouverture du golfe de Guinée au crétacé inférieur[END_REF].

In intracontinental Africa, a large alluvial basin (named hereafter the 'Saharan basin') has installed. It is separated from the margins of the Central and future Equatorial Atlantic margins by a wide erosional domain suggestive of a marginal upwarp. Thermochronological data (Gunnell, 2003;Leprêtre, 2015) as well as widespread kimberlitic magmatism are consistent with uplifts in this domain. Given paleocurrent data, erosion of the upwarp must have fed the Saharan basin, which is connected to the Tethys Ocean located further to the North (e.g., [START_REF] Guiraud | Phanerozoic geological evolution of Northern and Central Africa: An overview[END_REF][START_REF] Frizon De Lamotte | Style of rifting and the stages of Pangea breakup[END_REF]. Within the Saharan basin, the low resolution of biostratigraphic data does not allow deciding whether the Nara and Amded rifts or the Western and Central Rift System are active (Figure 3-1). Magmatic activity is widespread over Northern South America since the Latest Jurassic, inside and mostly outside the rifts. River systems crossing the future Equatorial Atlantic domain may still exist at the time.

CHAPTER 3 :PALEOGEOGRAPHIC AND STRUCTURAL RECONSTRUCTION Large-scale transpressional inversion structures (folds and oblique-reverse faults) affect the southern margin of the Guinea plateau [START_REF] Benkhelil | The Guinea continental margin; an example of a structurally complex transform margin[END_REF] and that of its South American counterpart in Guiana (the Demerara plateau; e.g., Sapin et al., 2016, Figure 3-1B and Figure 3-2).

This inversion takes place in the vicinity of the future Guinea fracture zone that separated the two plateaus, at the junction between the Central and future Equatorial Atlantic Oceans. Shortening also affects intracontinental South America, forming several major arches along sedimentary basins' margins. These features indicate that transform/oblique rifting of the Equatorial Atlantic domain responded to plate reorganization (e.g., [START_REF] Benkhelil | The Guinea continental margin; an example of a structurally complex transform margin[END_REF]. The southern jump of the rotation pole of the African plate led to the abandonment of part of the South American rifts, stopping South-to Southeastward propagation of the Central Atlantic Ocean into South America and enhancing transform rifting along a new small circle. Aptian plate reorganization that caused the opening of the Central Atlantic Ocean and induced major inversion along the Guinea fracture zone is also attested by the telescoping pattern of transforms of the Southern Central Atlantic Ocean towards that transform [START_REF] Bouysse | Geological Map of the Word[END_REF]. [START_REF] Benkhelil | Structure et évolution géodynamique du bassin intracontinental de la Bénoué (Nigeria): Sociéte Nationale Elf-Aquitaine[END_REF][START_REF] Benkhelil | Sedimentary and structural characteristics of the Cretaceous along the Cote d'Ivoire-Ghana transform margin and in the Benue Trough; a comparison[END_REF]. A delta forms in the middle of the Trough, forming a transition between the Sahara basin and the Equatorial Atlantic

Ocean. That delta appears to be fed from the southernmost Saharan basin and by longitudinal drains of the South Atlantic marginal upwarp of Africa. A coastal plain develops in a very large embayment on South America, attesting to the very low regional continental slopes. The surface of exposed land has not evolved significantly since the Aptian in West Africa. The northwestern African marginal upwarp feeds both the Saharan basin and the margins. From this time on, no river systems will connect Africa to South America.

Late Cenomanian (97-93Ma): Maximum Continental

Flooding (Figure 3456789)

The global maximum transgression during the Late Cenomanian-Early Turonian allows the flooding of the Hoggar Shield. This 'Trans-Saharan Seaway' connects the Tethys Ocean, in the north, to the Equatorial Atlantic Ocean, in the south [START_REF] Reyment | Biogeography of the Saharan Cretaceous and Paleocene epicontinental transgressions[END_REF][START_REF] Luger | Paleobiogeography of late Early Cretaceous to early Paleocene marine Ostracoda in Arabia and north to Equatorial Africa[END_REF], and shallow marine brackish shales and limestones are deposited above the 'Continental Intercalaire' [START_REF] Doucouré | Réalité des communications marines transsahariennes entre la Téthys et l'Atlantique durant le Crétacé supérieur[END_REF][START_REF] Zanguina | An Introduction to the Petroleum Potential of Niger[END_REF]. Thermochronological data suggest burial of the Hoggar and Reguibat shields ( (Rougier et al., 2013;Leprêtre et al., 2014;[START_REF] English | Intraplate uplift: New constraints on the Hoggar dome from the Illizi basin (Algeria)[END_REF], consistent with subsidence under the 'Trans-Saharan seaway" and the northwestern Sahara basin, respectively. A wide lagoonal and coastal domain forms between these two domains, undergoing alternating transgressions and regressions [START_REF] Fabre | Evolution des terrains mésocénozoïques d'une marge à l'autre du craton ouest africain, entre le Tanezrouft (Algérie) et l'Adrar de Mauritanie[END_REF]. The Upper Benue trough still receives deltaic and coastal sediments mostly provided by the South Atlantic marginal upwarp. Upper Cenomanian-Turonian marine transgression is recorded along the Central and Equatorial Atlantic margin without significant inland shoreline migration [START_REF] Brownfield | Assessment of the undiscovered oil and gas of the Senegal Province, Mauritania, Senegal, the Gambia, and Guinea-Bissau[END_REF]Baby et al., 2014). This suggests a relatively steep seaward topographic slope of the continent. That transgression is documented further inland in South America in at least two embayments, suggesting a lower seaward topographic slopes on that side of the Equatorial Atlantic. Transform faults are still active during the Late Cenomanian, as the mid-ocean ridges slide against the Ivory Coast-Ghana marginal ridge (i.e., the 'active transfrom margin' stage of [START_REF] Basile | Phanerozoic geological evolution of the Equatorial Atlantic domain[END_REF]. During this stage, anticlines form at the African tip of the Romanche and Saint Paul transform faults as a result of transpressional reactivation. The Equatorial Atlantic Ocean deepens and develops restricted bottom water circulation as attested by paleontological evidence (black shales and Oligosteginid limestone) [START_REF] Chierici | Stratigraphy, palaeoenvironments and geological evolution of the Ivory Coast-Ghana basin[END_REF][START_REF] Dumestre | The petroleum geology of the Republic of Guinea Bissau[END_REF][START_REF] Brownfield | Geology and total petroleum systems of the Gulf of Guinea Province of West Africa[END_REF].

In Africa, the area exposed to erosion does not change significantly. The marginal upwarp north of 20°N is flooded but a wider surface corresponding to the Man-Leo shield and the southern Taoudeni basin is now undergoing erosion. The South Atlantic marginal upwarp feeds the Trans-Saharan Seaway and a river system in the Chad basin connecting potential source areas in East Africa to the Trans-Saharan Seaway may not be precluded. During the Santonian, sinistral transpression leads to the inversion of the Benue Trough, producing regional folds, cleavages and schistosities and forming a mountain range that recorded ca.12 km of shortening (Benkhelil and Guiraud, 1980;Benkhelil, 1987[START_REF] Benkhelil | Structure et évolution géodynamique du bassin intracontinental de la Bénoué (Nigeria): Sociéte Nationale Elf-Aquitaine[END_REF][START_REF] Benkhelil | The Benue Trough; wrench-fault related basin on the border of the Equatorial Atlantic[END_REF]. The shortening direction varies from N to NW. Transpressional structures are also documented in the Western and Central Rift System [START_REF] Guiraud | Senonian basin inversion and rejuvenation of rifting in Africa and Arabia; synthesis and implications to plate-scale tectonics[END_REF], with shallow marine sediments deposited during inversion. A narrow seaway of the Tethys floods the Western and Central Rift System. This seaway is probably bounded by lagoonal environments to the West [START_REF] Fabre | Evolution des terrains mésocénozoïques d'une marge à l'autre du craton ouest africain, entre le Tanezrouft (Algérie) et l'Adrar de Mauritanie[END_REF]. The Hoggar Shield remains buried, as suggested by thermochronological data. Equatorial Atlantic Ocean and the Trans-Saharan Seaway [START_REF] Reyment | Biogeography of the Saharan Cretaceous and Paleocene epicontinental transgressions[END_REF][START_REF] Luger | Paleobiogeography of late Early Cretaceous to early Paleocene marine Ostracoda in Arabia and north to Equatorial Africa[END_REF]. It is likely that the connection is made through the Bida rift, which begins to form in the Campanian and continues to develop during the Maastrichtian under shallow marine environment [START_REF] Kogbe | Confirmation of a rift structure along the Mid-Niger Valley, Nigeria[END_REF][START_REF] Akande | Paleoenvironments, organic petrology and Rock-Eval studies on source rock facies of the lower Maastrichtian Patti Formation, southern Bida Basin, Nigeria[END_REF][START_REF] Ojo | Sedimentology and depositional environments of the Maastrichtian Patti Formation, southeastern Bida Basin, Nigeria[END_REF]. Transgression is also recorded on the Ivory Coast-Ghana and Ghana-Benin margins by the flooding of the coastal basins.

Stratigraphic architectures of the

The Western and Central Rift System is reactivated in extension and accommodates the deposition of alluvial sandstones [START_REF] Zanguina | An Introduction to the Petroleum Potential of Niger[END_REF]. A rapid filling of the rifts may explain the change in depositional environment from marine to continental, even though more accommodation space is created. Folding is probably still active in the Upper Benue Trough, resulting in a Maastrichtian unconformity [START_REF] Benkhelil | Benue Trough and Benue Chain[END_REF]. Reactivation of folding at the African tip of the Romanche transform fault is also active. Regional deformation seems to result from a W to WNW extension (and potentially shortening normal to that direction). Magmatism only affects the Lower Benue Trough and the adjoining Cameroun Line (Figure 3 favored by the peak greenhouse climate, allowing bauxites to develop all over the emerged lands [START_REF] Beauvais | Modes, tempo, and spatial variability of Cenozoic cratonic denudation; the West African example[END_REF][START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. The preservation of bauxites over the Nigerian Shield and the Bida rift [START_REF] Valeton | Bauxites and associated terrestrial sediments in Nigeria and their position in the bauxite belts of Africa[END_REF] precludes the connection between the Equatorial Atlantic Ocean and the Tethys [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. As continental chemical weathering is favored, correlative carbonates and phosphates are found in all West African basins and clastic fluxes through the river systems are subdued (e.g., [START_REF] Lang | The continental terminal in West Africa[END_REF][START_REF] Valeton | Bauxites and associated terrestrial sediments in Nigeria and their position in the bauxite belts of Africa[END_REF][START_REF] Johnson | Le bassin sedimentaire a phosphates du Togo (Maastrichtien-Eocene); stratigraphie, environnements et evolution[END_REF].

The size of the erosional domain did not evolve significantly and a continuous marginal upwarp re-installs.

CHAPTER 3 :PALEOGEOGRAPHIC AND STRUCTURAL RECONSTRUCTION Volcanism develops on the African plate from the Late Eocene onward at various locations outside the frame of the West African craton [START_REF] Burke | The African Plate[END_REF]. On the Hoggar shield and along the Cameroon line, this volcanism is interpreted as "hot-spot" related (e.g., [START_REF] Ait-Hamou | Le magmatisme cénozoïque du Hoggarௗ: Une synthèse des données disponibles. Mise au point sur l'hypothèse d'un point chaud[END_REF]Liégois et al., 2005;[START_REF] Ait-Hamou | Le volcanisme cénozoïque à l'échelle du bombement de l'Ahaggar (Sahara Central Algerien): synthèse géochronologique et répartition spatio-temporelle quelques implications en relation avec l'histoire eo-Alpine de la plaque Afrique[END_REF][START_REF] Ngako | The north-south Paleozoic to Quaternary trend of alkaline magmatism from Niger-Nigeria to Cameroon; complex interaction between hotspots and Precambrian faults[END_REF]; Appendix 1). The Hoggar Shield would undergo exhumation since the Late Eocene (40-30 Ma) as suggested by cooling temperaturetime paths of apatites (Rougier et al., 2013;[START_REF] English | Intraplate uplift: New constraints on the Hoggar dome from the Illizi basin (Algeria)[END_REF]. The products of its erosion are emplaced in mega fans of the 'Continental Terminal' around the massif that is undergoing uplift [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. Doming of the Hoggar shield leads to the individualization of the presentday intracontinental basins of Northwestern Africa by fragmentation of a single Saharan basin into the Taoudeni, South Algerian, Murzuk, Chad and Iullemmeden basins. This fragmentation contributed to the development of the "basin-and-swell" topography of the continent [START_REF] Burke | The African Plate[END_REF].

This triggered definitive retreat of the sea from the continent and a major drainage reorganization, which led to the establishment of the modern river network during the Early Oligocene, allowing for the building of the Niger delta [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. As a consequence of possible uplift by the development of the basin-and-swell topography, numerous canyons incise the shelf and slopes of the Equatorial and South Atlantic margins of Africa, starting in the late Early Oligocene [START_REF] Simon | La discordance oligocène et les dépôts posterieurs a la discordance dans le bassin sédimentaire ivoirien[END_REF][START_REF] Burke | The African Plate[END_REF][START_REF] Seranne | Oligocene to Holocene sediment drifts and bottom currents on the slope of Gabon continental margin (West Africa); consequences for sedimentation and Southeast Atlantic upwelling[END_REF]this work). Some authors suggest that the Western and Central Rift System is reactivated in the Eocene-Early Oligocene, allowing for the deposition of fluvial-lacustrine sediments (Genik, 1992(Genik, , 1993;;[START_REF] Zanguina | An Introduction to the Petroleum Potential of Niger[END_REF]. A phase of lateralization affects the entire sub region until the Latest Oligocene [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. No sediment accumulates on the continent from that time on, except in the intracontinental Chad basin that still subsides during the Neogene [START_REF] Burke | The Chad Basin: an active intra-continental basin[END_REF].

Discussion

Rifting and Large-scale Kinematics

Our reconstruction of the Albo-Aptian rifting stage (Figure 3-7) shows that the network formed by the Equatorial rift system and the intracontinental African rifts subdivides the continent areas into 7 microplates . This configuration allows for refining the kinematic framework for Early Cretaceous rifting that is usually based on a 4 microplates model (South America, NW Africa, Nubia and Central/Southern Africa; e.g., [START_REF] Guiraud | Early Cretaceous rifts of Western and Central Africa: an overview: Tectonophysic[END_REF][START_REF] Maurin | Basement control in the development of the Early Cretaceous West and Central African Rift System[END_REF]. A central Microplate 1 (Leo-Man and Nigerian shields, Figure 1B) is bounded to the SW by the en-échelon Equatorial rift system and to the E by the Gao-Bida rift system (Figure 3-14). The northwestern limit is a transfer fault system in the direction of the Guinea-Demerara plateaus bounding fault, the Nara rift and the Amded rift (Figure 3 But their width and/or the evolution of their width through time suggests that asthenosphere dynamics or lithosphere-asthenosphere interactions were involved in their maintenance or rejuvenation.

Implications for Paleogeographic and Source-to-Sink studies

The space / time relationships between margins, marginal upwarps, intracratonic basins and hot-spot swells revealed by the present work have implications for understanding long-wavelength continental deformation and associated sedimentary processes of paired shield areas/continental margin systems.

Marginal upwarp segments constitute long-lived source areas for clastic sediments.

However, beyond the two Paleogene time steps (Figure 3-12 and Figure 3-13), the past river networks and continental divides may not be inferred. Yet, the present work helps addressing key issues for the understanding of passive margin -cratonic areas source-to-sink systems. Our reconstructions and paleocurrent data suggest that river systems draining the upwarp(s) fed both the intracratonic Saharan basin and the Central and Equatorial Atlantic margins since at least lithospheric break-up. The source-to-sink sediment budget of marginal upwarp should therefore consider both the margin and -potentially distant -intracratonic sinks, be they marine or continental.

Given that the Saharan basin was a large embayment of the Tethys Ocean located north of the study area, remobilization and northward transport of its sediments have occurred. Furthermore, our reconstructions indicate that Meso-Cenozoic sediments have been tapped from the intracratonic basin and transported to the margin basins by rivers cutting across upwarp(s). This implies that intracratonic basins are transient sediment reservoirs (i.e., sinks) that have to be taken into account for source-to-sink investigations of marginal upwarps. This issue is further amplified by the Late Paleogene upheaval of the Saharan basin as a consequence of hot-spot swell growth (Figure 3-3D), which renders assessment of Mesozoic intracratonic sedimentary accumulation uncertain. In any case, our study provides ways to assess the past areal extent of erosional marginal upwarps, which may be used to estimate volumetric erosional export of such upwarps using long-term denudation laws such as those calibrated by [START_REF] Beauvais | Modes, tempo, and spatial variability of Cenozoic cratonic denudation; the West African example[END_REF] or [START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF][START_REF] Grimaud | Neogene cratonic erosion fluxes and landform evolution processes from regional regolith mapping (Burkina Faso[END_REF].

Conclusion

The The geological reconstructions reveal the persistent / renewed occurrence of eroding upwarps along the African continental margins that provided sediments both for the margin basins and for a very large, persistent intracratonic basin. But as an embayment of the Tethys Sea, such a basin acted as a transient sediment reservoir because the products of it erosion were transferred both to the Tethys (by north-flowing rivers) and the Equatorial Atlantic Ocean (by rivers crossing the marginal upwarp(s)). The source-to-sink investigation of the paired shield area-continental margin system is further complicated by Late Paleogene upheaval of the intracratonic basin as a result of hot-spot swell growth that led to the distortion and further massive erosion of its Meso-Cenozoic sediments. Upheaval resulted in the fragmentation of the intracratonic basin into the current, smaller residual basins, whose pre-hot-spot evolution should not be considered separately from one another. Hot-spot swell growth triggered a major reorganization of both the continental area and its margins in the Early Oligocene, so has the Northwest African source-to-sink system.

Acknowledgments

Introduction

The African Equatorial Atlantic margin is known for its transform-controlled evolution, leading to the final opening of the Atlantic Ocean [START_REF] Mascle | Development of a passive transform margin: Côte d'Ivoire-Ghana transform margin -ODP Leg 159 preliminary results[END_REF][START_REF] Basile | Phanerozoic geological evolution of the Equatorial Atlantic domain[END_REF]. Most of previous investigations have focused on the evolution of the Ghana transform margin at the intersection of the Romanche transform fault with the West African craton [START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF][START_REF] Attoh | Seismic stratigraphic record of transpression and uplift on the Romanche transform margin[END_REF][START_REF] Antobreh | Rift-shear architecture and tectonic development of the Ghana margin deduced from multichannel seismic reflection and potential field data[END_REF]. As a spectacular feature of that part of the transform margin, the Ivory Coast-Ghana marginal ridge has been investigated by geophysical cruises, scientific drilling (Ocean Drilling Program, Leg 159) and deep-sea dives [START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF][START_REF] Mascle | Development of a passive transform margin: Côte d'Ivoire-Ghana transform margin -ODP Leg 159 preliminary results[END_REF][START_REF] Benkhelil | Submersible observations of Cretaceous deformations along the Côte d'Ivoire-Ghana transform margin[END_REF]Clift et al., 1998;Bouillin et al., 1998;Pletsch et al., 2001, Figure 4-1). These studies mainly showed the structure of the ridge, the geometry of the shallow Eastern Ivory Coast and highlighted vertical displacements of the marginal ridge during the intracontinental rift and syn-transform stages. Most of the other studies (e.g., Sierra Leone-Liberia, Eastern Ivory Coast segments) focused mainly on the structuration and sedimentation during the syn-rift or, locally, the post-rift stratigraphic architecture in terms of petroleum potential, as increasing interests have been given on deep-water turbidite reservoirs [START_REF] Grillot | Three-dimensional seismic interpretation; Espoir Field area, offshore Ivory Coast[END_REF][START_REF] Kjemperud | Tectonostratigraphic history of the Keta Basin, Ghana with emphasis on late erosional episodes[END_REF][START_REF] Bennett | Regional 2D seismic interpretation and exploration potential of offshore deepwater Sierra Leone and Liberia[END_REF][START_REF] Macgregor | Play fairways of the Gulf of Guinea transform margin[END_REF][START_REF] Flinch | The Sierra Leone-Liberia Emerging Deepwater Province: AAPG Search and Discovery[END_REF].

The equatorial Atlantic margin does however show a very complex 3D pattern of [START_REF] Benkhelil | Structure et évolution géodynamique du bassin intracontinental de la Bénoué (Nigeria): Sociéte Nationale Elf-Aquitaine[END_REF][START_REF] Benkhelil | The origin and evolution of the Cretaceous Benue Trough (Nigeria)[END_REF].

Regional Settings

The rifting of the Equatorial Atlantic Ocean propagated eastward from the Central Atlantic between the Valanginian (ca. 140 Ma) and the Aptian (ca. 112 Ma) as an en-échelon transform-rift system (e.g. [START_REF] Macgregor | Play fairways of the Gulf of Guinea transform margin[END_REF][START_REF] Brownfield | Geology and total petroleum systems of the Gulf of Guinea Province of West Africa[END_REF] with a main rift phase in the Middle Aptian (120-115 Ma; Ye et al., Submitted). This rift was connected to a large inland rift network [START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF]Heine and Brune, 2014, Ye et al., Submitted) and initially formed continental pull-apart basins. The breakup of the continent leading to the formation of the Equatorial Atlantic Ocean started later on, although the deformation history appears to be more complex than a simple combination of coeval transform and normal faulting (Ye et al., submitted).

It is not well constrained because the age of the first oceanic crust was not precisely dated during the 'Cretaceous Quiet Magnetic Period' [START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF][START_REF] Heine | Kinematics of the South Atlantic rift: Solid Earth[END_REF]Ye et al., Submitted). Seafloor spreading or mantle exhumation initiated locally, during the Aptian-Early Albian (125-107 Ma), within isolated basins in Ivory Coast and Guinea bounded by major transform faults in Ivory Coast and Guinea. The paleobathymetry of these newly formed "oceanic basins" deepened slowly. They were flooded during the Late Albian although they remained under restricted water circulation during the Albo-Cenomanian [START_REF] Chierici | Stratigraphy, palaeoenvironments and geological evolution of the Ivory Coast-Ghana basin[END_REF]Ye et al., Submitted). ) achieving the segmentation of the African Equatorial margin. This break-up was associated with a major regional unconformity, the "Breakup Unconformity", also observed on the conjugate Brazilian margins [START_REF] Zalan | Bacia do Marajo[END_REF][START_REF] Junior | Bacia de Barreirinhas[END_REF][START_REF] Soares Júnior | Evolução do rifteamento e paleogeografia da margem Atlântica Equatorial do Brasil[END_REF]). An 'active-transform' stage lasting until the Late Santonian (ca. 84 Ma) can be defined during the passage of oceanic spreading ridge along the transform segments in Western Ivory Coast and Ghana [START_REF] Basile | Phanerozoic geological evolution of the Equatorial Atlantic domain[END_REF]. A "Senonian Unconformity" was identified as a strong angular unconformity, corresponding to a hiatus of Turonien-Early Senonian (94-84 Ma) in Eastern Ivory

Coast and Santonian-Campanian (86-72 Ma) in Benin [START_REF] Elvsborg | Benin hydrocarbon potential looks promising[END_REF][START_REF] Chierici | Stratigraphy, palaeoenvironments and geological evolution of the Ivory Coast-Ghana basin[END_REF].

Its origine is debated, but it could be related to the Santonian tectonics in the Benue Trough or the last transtensional movements affecting the Equatorial Atlantic margin [START_REF] Chierici | Stratigraphy, palaeoenvironments and geological evolution of the Ivory Coast-Ghana basin[END_REF][START_REF] Brownfield | Geology and total petroleum systems of the Gulf of Guinea Province of West Africa[END_REF]. Once the oceanic ridges passed beyond their outer corner tip, the transform margins entered a passive-margin stage [START_REF] Basile | Transform continental margins; Part 1[END_REF].

Material and Method

Dataset

Figure 4-2 Location of interpreted seismic sections and the exploration wells used for proximal deposits analysis. Segmentation of the Equatorial Atlantic margin used in this study is shown by dashed color lines.

Our study of the African Equatorial Atlantic margin was based on a large set of subsurface data (about 1000 seismic reflection lines and 70 exploration wells) located along the margin from Sierra Leone to Benin (an area of c. 2.3x10 5 km 2 , Figure 4-2) among which we selected eleven composite regional sections perpendicular to the shoreline and extending from the present-day shelf to the abyssal plain (Figure 4-2). Thirty-eight of those wells have been recently evaluated in terms of biostratigraphy (palynology, nanofossil, foraminifera dating) by TOTAL, most of them located on the present-day shelf. We used them for calibration in ages of the stratigraphic surfaces. For three wells of the shelf of Western Ivory Coast (Figure 4-2), we also used well-logs, including Gamma Ray (GR, for radioactivity), Spontaneous Potential (SP, for permeability), Sonic (Dt), Netron (NPHI), Density (RHOB) and Resistivity as well as available cuttings reports, for lithologic calibration and paleo-environemental interpretations [START_REF] Van Wagoner | An overview of the fundamentals of sequence stratigraphy and key definitions[END_REF], 1990;[START_REF] Homewood | Corrélations Haute Résolution et Stratigraphie Génétique: Une Démarche Intégrée[END_REF].

Seismic Stratigraphy

We defined the stratigraphic architecture using the offlap migration method [START_REF] Vail | Seismic Stratigraphy and Global Changes of Sea Level: Part 3. Relative Changes of Sea Level from Coastal Onlap[END_REF][START_REF] Helland-Hansen | Shoreline trajectories and sequences; description of variable depositional-dip scenarios[END_REF][START_REF] Homewood | Corrélations Haute Résolution et Stratigraphie Génétique: Une Démarche Intégrée[END_REF]. It is based on the identification of offlap breaks that correspond to the slope rupture of clinoforms (Figure 4-3). They represent either past shorelines or past shelf-breaks. Their nature (shoreline or shelf-break) is identified by the upstream sedimentary environments that can be constrained by well-logs data.

When an offlap break is identified as a shoreline, its migration trajectory allows to define trends of or transgressive surfaces (TS), mark the inversion from a propagradation to a retrogradation.

Transgression/regression sequences are determined as bordered by these key surfaces including a propagradational system tract (highstand, lowstand and forced regression system tracts) and a retrogradational system tract (transgressive system tract, Figure 4-3c). A highstand system tract is separated from a lowstand or forced regression system tracts (downward shift of offlap break) by an unconformity, and from transgressive system track by a maximum flooding surface.

A transgressive system track, usually less well preserved, is separated from lowstand system track by a flooding surface.

Structural and Stratigraphic Characteristics of the

Segments

We mapped the continent-ocean boundary (COB) and the different crustal domains (thinned continental crust, hyperextended curst/continent-ocean transition, oceanic crust, Figure 4-2). We then focused on the early post-rift history of the margin, i.e., the Upper Cretaceous stratigraphic architecture. We mapped four regional horizons in every basin (Figure 5-2). Regional unconformities, such as the Late Albian Breakup and Senonian (probably Santonian, ca. 84 Ma)

unconformities were correlated from one margin segment to the other, as well as the major Cenomano-Turonian maximum flooding surface (ca. 94 Ma). The Campanian sub-regional unconformity surface (ca. 72 Ma) was mapped only along the Sierra Leone-Liberia and Ivory Coast margins. We then classified each margin segments according its structural and stratigraphic characteristics (Figure 4-2).

Ivory Coast Margin

Crustal Along the Eastern divergent segment, the syn-rift normal faulting is better expressed. On the other hand, the continent-ocean boundary (COB) is less clear. Indeed, a hyperextended domain, considered also as COT, has been identified between a thinned continental crust and a typical oceanic crust (Figure 4-4b andc). Faulting and thinning of that domain seems to support its continental nature. This hyperextended crust domain is widening from the NW to the SE (Figure

Ghana Margin

The Ghana segment has been previously investigated but mostly at its Western tip, at the location of the Ivory Coast-Ghana marginal ridge [START_REF] Mascle | Evidence for transform margin evolution from the Ivory Coast-Ghana continental margin[END_REF][START_REF] Basile | Geodynamic evolution of the Cote d'Ivoire-Ghana transform margin; an overview of Leg 159 results[END_REF]Bouillin et al., 1998;Clift et al., 1998;[START_REF] Bigot-Cormier | Denudation of the Côte d'Ivoire-Ghana transform continental margin from apatite fission tracks[END_REF]

Sierra Leone-Liberia Margin

The Sierra Leone-Liberia margin is composed of both the Sierra Leone segment and the Liberia As a difference, the Liberia segment shows a narrower necking zone (ca. 30 km; Figure 4-8c andd). The syn-rift fault pattern is not well imaged, but could be associated with landward tilted blocks with fan-shape syn-rift deposits observed only very locally in one proximal half-graben.

Most of syn-rift deposits form seaward reflectors, suggesting interbeded volcanic lava flows.

Aptian-Albian and Jurassic interbedded basalts and tuffs have indeed been drilled [START_REF] Bennett | Regional 2D seismic interpretation and exploration potential of offshore deepwater Sierra Leone and Liberia[END_REF]. If these reflectors are indeed Jurassic in age, i.e. contemporaneous of the Central Atlantic Magmatic Province (CAMP), this suggests an earlier phase of stretching of the crust of this segment during the Central Atlantic rifting. Triassic to Early Jurassic desertic sands and basalts have indeed been identified in the Foz do Amazonas basin, along the South American conjugate margin of the Sierra Leone-Liberia segment [START_REF] Figueiredo | Bacia da Foz do Amazonas[END_REF]. Furthermore, the NW-trend of the Sierra-Leone margin segment matches the Central Atlantic opening direction, as well as a NW-trending transform system identified along the Liberia margin segment on the seafloor CHAPTER 4 :STRUCTURE AND MESOZOIC STRATIGRAPHY OF THE EQUATORIAL ATLANTIC MARGIN 128 bathymetry [START_REF] Bennett | Regional 2D seismic interpretation and exploration potential of offshore deepwater Sierra Leone and Liberia[END_REF]. These observations would be consistent with deformation of the Liberia margin segment during the Triassic-Early Jurassic prior to the Equatorial Atlantic rifting.

We therefore suggest that the Sierra Leone-Liberia margin experienced a first extensional deformation during the Triassic-Early Jurassic, related to the Central Atlantic rifting, forming the southernmost rifts of that system. The main rifting followed during the Lower Cretaceous rifting of the Equatorial Atlantic. The structural contrast between the Sierra Leone and the Liberia margin segments also suggests different syn-rift deformation regime (Figure 4-2 and Figure 45678). Along the Liberia segment, deep structures have been identified within the crust that may be attributed to older deformations events, such as the Neoproterozoic Panafrican and Hercynian orogens. These may have imprinted the continental lithosphere rheology, and in doing so, influenced the segmentation.

The Upper Cretaceous early post-rift stratigraphic architecture also varies between the Sierra Leone to Liberia segments. In Liberia, Upper Cretaceous deposits were mostly preserved in the distal part of the margin, forming a fan-shape wedge onlapping landward and downlapping seaward as along the Western Ivory Coast and Ghana transform segments. As a difference, along the Sierra Leone segment, the distal Upper Cretacous geometry seems to be affected by a complexe paleorelief of the margin basement at the end of the rifting. Numerous turbiditic systems can be observed within those distal deposits, suggesting multiple point sources along the margin during the Upper Cretaceous (e.g. [START_REF] Reading | Turbidite systems in deep-water basin margins classified by grain size and feeder system[END_REF].

These observations suggest that the difference in syn-rift deformation regimes along the Liberia -Sierra Leone segments has also had a strong influence on the immediate post rift history of this segment.

CHAPTER 4 :STRUCTURE AND MESOZOIC STRATIGRAPHY OF THE EQUATORIAL ATLANTIC MARGIN

Figure 4-8 Structural and stratigraphic Interpretation of regional cross-sections along the Sierra Leone-Liberia margin segment. See location in Figure 4-2.

Margin Segmentation

The segmentation of the African Equatorial Atlantic margin from Sierra Leone to Benin is controlled by transform faults (Figure 4-2). The early post-rift stratigraphic architectures vary from one segment to another, with different deformation regimes (Figure 4-9). We discuss here the impact of this segmentation on present day crustal geometry and on post-rift stratigraphic architecture. To do this, we first measured the obliquity of each segment as the angle between the relative plate motion direction (given by the orientation of transform fault) and the regional trend of margin segment (given by the orientation of the COB). Transform margin segments have therefore a 0° obliquity, whereas divergent segments of the Equatorial Atlantic have a 75° obliquity (Figure 4-10). The Togo-Benin segment, with a 30° obliquity is an intermediate oblique segment.

Also, the Sierra Leone-Liberia segment is transform with respect to the Central Atlantic system, but oblique with respect to the Equatorial Atlantic.

Regimes of Crustal Stretching and Obliquity

The width of the necking zone increases with the obliquity of the margin segments: from less than 40 km along transform segments to over 100 km along divergent ones (Figure 4-10).

Different 3D deformation regimes along transform and divergent segments (strike-slip vs normal faulting) can explain this relationship between obliquity and the necking width of a segment. This relationship is however not preserved, when crustal stretching involved several stages. Indeed, Breakup unconformity were compiled from regional sections and superposed at the major slope rupture of horizon.

Note that the horizons were with a two-way time axe, but not in depth, and only the relative angle between horizons of different margin segments should be considered.

The cause of variations of obliquity from one segment to the other is not clear. Pre-existing crustal weakness (e.g. Panafrican orogeny) or fault patterns may act as inheritance and influence the localization of deformation and syn-rift faulting orientations. Nevertheless, the Ivory Coast margin formed by cutting through the West African craton, separating the southernmost part on the South American side (Klein and Moura, 2008b) and this does not support an inheritance controlled obliquity. Deep mantle anomalies may impact lithospheric deformation localization by modifying the thermal field [START_REF] Koptev | Dual continental rift systems generated by plume-lithosphere interaction[END_REF][START_REF] Koptev | Contrasted continental rifting via plume-craton interaction: Applications to Central East African Rift[END_REF]. This may be expressed by magmatism on the surface during the rifting that has been documented only sparsely along the Equatorial Atlantic margins during the Valanginian-Late Albian (140-100 Ma, Ye et al., Submitted).

Early Post-rift Stratigraphic Architecture

The stratigraphic architecture of the early post-rift (Upper Cretaceous) in the proximal domain also shows major differences in the two end-members type of segments (transform and divergent; To further characterize the geometry of the early post-rift wedge, we measured, along every segment, the present-day averaged maximum slopes of the reflectors corresponding to the seafloor, the K-T boundary reflector and the Breakup Unconformity reflector (Figure 4-10). This analysis shows that the present-day slope of those surfaces increases as the obliquity of margin decreases (from transform to divergent segments) everywhere except along the Liberia segment. This suggests that a first-order control on the post-rift stratigraphic architecture is the structuration of margin segment during the syn-rift, and in particular, its obliquity.

Vertical Displacements

Our observations suggests that the different segments of the African Equatorial Atlantic Upper Cretaceous sediments first deposited on the shelf, then removed, in response to uplift driven accommodation reduction on the shelf.

In the case of transient event of shelf uplift, several mechanisms could cause it during the Upper Cretaceous along the Equatorial Atlantic margin: (1) a regional tectonic compression that has been documented in the Benue Trough during the Santonian inversion [START_REF] Benkhelil | The origin and evolution of the Cretaceous Benue Trough (Nigeria)[END_REF][START_REF] Guiraud | Senonian basin inversion and rejuvenation of rifting in Africa and Arabia; synthesis and implications to plate-scale tectonics[END_REF], (2) an uplift in response to a change in lateral stress regime and a change in spreading direction [START_REF] Fairhead | Differential opening of the Central and South Atlantic Oceans and the opening of the West African rift system[END_REF], or (3) mantle upwelling or edge convection under the margin [START_REF] Matton | The Cretaceous Peri-Atlantic Alkaline Pulse (PAAP): Deep mantle plume origin or shallow lithospheric break-up?[END_REF]. In the case of a more steady uplift counteracting subsidence of the proximal domain of the margin during the Upper Cretaceous, two main causes may be invoked. First, the flexural response of the stretched lithosphere to the thermal subsidence load and erosion/sedimentation (un)loading may induce an uplift in the proximal part of the margin, in particular during the early post-rift (e.g. [START_REF] Rouby | Long term stratigraphic evolution of Atlantic-type passive margins; a numerical approach of interactions between surface processes, flexural isostasy and 3D thermal subsidence[END_REF]. It has been shown

that the narrower the necking zone, the larger the associated flexural uplift (e.g. [START_REF] Van Der Beek | Cenozoic landscape development in the Blue Mountains (SE Australia); lithological and tectonic controls on rifted margin morphology[END_REF][START_REF] Rouby | Long term stratigraphic evolution of Atlantic-type passive margins; a numerical approach of interactions between surface processes, flexural isostasy and 3D thermal subsidence[END_REF]. However, this Upper Cretaceous post-rift margin rejuvenation was also observed along other Atlantic margins, such as the North America margin (uplift at 85-65 Ma; [START_REF] Amidon | Late Cretaceous unroofing of the White Mountains, New Hampshire, USA; an episode of passive margin rejuvenation? Geology[END_REF], the NE Brazil margin (84-72 Ma; [START_REF] Turner | Thermal history of the Rio Muni (West Africa)-NE Brazil margins during continental breakup[END_REF][START_REF] Japsen | Episodic burial and exhumation in NE Brazil after opening of the South Atlantic[END_REF].

The synchronous Upper Cretaceous rejuvenation over such a broad region suggests an alternative explanation of a very large-scale process (x 100-1000 km), such as mantle upwelling. Those two processes (flexure and mantle driven deformation) are not mutually exclusive.

Conclusion

We analyzed the structural variability of the various segments of the African Equatorial Atlantic margin as well as the stratigraphic architecture of their early post-rift sedimentary wedge.

(i) Segmentation of the margin has been, at least partly, driven by transform faults, defining segments with different obliquities with respect to their orientation. Obliquity increases from transform to divergent segments, along with the width of the crustal necking zone.

(ii) Early post-rift stratigraphic architecture appears to be largely controlled by this obliquity: transform segments show steeper slopes of all the post-rift horizons than divergent segments. This correlation between obliquity and post-rift stratigraphy was however not observed, when the margin underwent a more complexe rifting history, such as the Sierra Leone-Liberia margin.

(iii) Also, the preservation of the early post-rift sedimentary wedge in the proximal domain differs in transform and divergent segments. Upper Cretaceous shallow deposits are preserved along divergent segments, whereas, on the shelf of transform segment, Cenozoic sediments lie directly on the Late Albian Breakup unconformity. Further comparison with the conjugate margin in South America would provide insights in understanding the mechanisms driving margin segmentation and would allow for further deciphering of the relative contribution of syn-rift deformation inheritance and regional mantle or plate dynamics on the early post-rift evolution of those margins.

Ackowledgments

Total Exploration and Production funded this study through the Transform Source-to-Sink Project (TS2P). We acknowledge Total for providing data and for allowing publication of the study.

Total R&D research group is thanked for discussions as well as scientific and technical support.

Introduction

In order to investigate how the sedimentary accumulation history of the Equatorial Atlantic margin is related to changes in the continental erosion in the drainages areas of the craton, we evaluated the volumes of Meso-Cenozoic sediments of each basin (Master 2 project, A. Loparev).

We used a cross section-based method [START_REF] Guillocheau | Quantification and causes of the terrigeneous sediment budget at the scale of a continental margin; a new method applied to the Namibia-South Africa margin[END_REF] where the terrigenous solid volume of accumulated sediments for each time interval is quantified by interpolation of regional cross-sections and then corrected from in situ carbonate production and remaining porosity after compaction. We also estimated uncertainties in the estimated solid volume. The temporal variation of accumulation gave insights into the filling history of each basin, as well as the variations in continental relief triggered by possible climate and deformation events.

Material and Method

Data

To estimate the volume of sediments accumulated in the Equatorial Atlantic basins (Ivory Coast, Ghana-Benin and Sierra Leone-Liberia basins), we used various types of data (Figure 5-1):

exploration seismic profiles and well data provided by TOTAL, published vintage seismic profiles [START_REF] Emery | Continental margin off western Africa; Angola to Sierra Leone[END_REF], bathymetric and basement maps (ETOPO5, [START_REF] Laske | A Global Digital Map of Sediment Thickness: EOS Trans[END_REF], and age of oceanic crusts [START_REF] Milesi | Tectonic Map of Africa[END_REF].

We used four Cretaceous horizons interpreted from Sierra Leone to Benin: Top Albian The estimation of solid volume and accumulation rates include the following 6 steps:

x TWT to Depth Conversion,

x cross-sections extrapolation,

x volume and accumulation rate estimation,

x in situ production correction,

x porosity correction,

x uncertainties estimation.

TWT to Depth Conversion

The first step is to convert selected horizons from two-way time (TWT) to depth (Km). For doing this, we defined a different velocity law for each basin.

In the Ghana-Benin basin, we used a two-layer velocity law: one layer for the Cenozoic, and another for the Upper Cretaceous. For each layer we used a linear function ( 1), taking into account the increase of velocity with depth due to compaction (see Japsen, 1993 for further explanation):

ܸሺݖሻ ൌ ܸ ݖ݇ (

Volume and Accumulation Rate Estimation

The principle of the method [START_REF] Guillocheau | Quantification and causes of the terrigeneous sediment budget at the scale of a continental margin; a new method applied to the Namibia-South Africa margin[END_REF]

In situ Production Correction

In order to extract the terrigenous portion of the deposited volume, which is the only part of the sediments that can be compared with eroded crust, we estimated and removed the content of Other in situ productions, such as volcanics, cherts and organic matters were not estimated here assuming they were negligible since they had been observed only locally in a limited number of wells [START_REF] Pletsch | Cretaceous separation of Africa and South America; the view from the West African margin (ODP Leg 159[END_REF].

Porosity Correction

Porosity remaining after compaction must be also corrected in order to obtain the solid volume of terrigenous sediments. Porosity decreases with depth and compaction and depends on the sediment lithology. We used an exponential law (4) (Figure 5-8):

ሺݖሻ ൌ  ݁ ି௭ (4)
Where (z) is the porosity at depth z,  the porosity at the surface and c the compaction factor depending on the lithology. In this study,  is equal to 49% for sand, and 63% for clay. c is 3700 km -1 for sand and 2000 km -1 for clay. Averaged porosity (ȁሻ between the depth z1 and z2 was then obtained by:

ȁ ൌ ሺ  బ ሻ ష భ ି ష మ ௭ భ ି௭ మ (5)
The solid volume was estimated by the equation ( 6):

ݏܸ ൌ ሺͳ െ ȁሻܸݐ (6)
where Vs is the solid volume, Vt the total volume.

Uncertainties on Absolute Ages

We used bio-stratigraphic data at well locations to attribute stratigraphic ages to depth converted horizons. We then ascribed absolute ages according to the UNESCO 2015 stratigraphic chart. Age attribution, whether stratigraphic or absolute, is associated with some uncertainty that we estimated for each horizon assuming larger uncertainties for unconfomities (Figure 5-2).

Uncertainties of Solid Accumulated Volume and Accumulation Rate

We estimated global uncertainties on estimated solid volumes and rates resulting from four sources of uncertainties:

x absolute ages of sediments,

x TWT-depth conversion law,

x carbonate content estimates,

x porosity correction.

To do this, volumes for each interval are calculated over 10000 times applying a random sampling of a value of each parameter within its variability. The standard deviation of the resulting values gave the uncertainty of the estimated volume or rate for each time interval.

Upper Cretaceous Sedimentary Budget

Non-extrapolated volumes show a peak of deposited volume during the Cenomanian in Sierra Leone-Liberia, which is followed by a decrease in volume (from about 9.1 to 6.7 x10 13 m 3 ) until the Campanian (Figure 5-9A). A new peak of volume appears during the Maastrichtian (about 1.1x10 14 m 3 ). The trend of accumulation rates is similar: they decrease from about 1.4x10 13 m 3 /Ma to 9.4x10 12 m 3 /Ma during the Cenomanian-Santonian, then increase to a maximum rate of about 1.9x10 13 m 3 /Ma. The accumulation volumes and rates follow the same trend in Ghana-Benin basin although with lower of magnitude. Maastrichtian peak was not observable because of the lower time resolution in this basin. Ivory Coast recorded a different accumulation history with a peak during the Campanian (about 8.2x10 13 m 3 ). Accumulation rates show a Maastrichtian peak and Cenomanian increase in accumulation cannot be excluded given uncertainties. Extrapolation of cross-sections increases the accumulated volume values in Sierra Leone-Liberia and Ivory Coast basin, but they remain within the same order of magnitude (Figure 5-9B). In terms of accumulation rates, the trend is similar in Sierra Leone-Liberia and Ivory Coast, with one peak in the Cenomanian (about 1.1x10 13 m 3 /Ma) and the other in the Maastrichtian (about 2.0x10 13 m 3 /Ma).

These results show that sediment accumulation along the whole African Equatorial Atlantic margin during the Late Cretaceous is associated with two peaks: one during the Cenomanian and the other one in the Maastrichtian. The Cenomanian peak could be associated with the erosion of rift shoulders, which formed by lithospheric flexural isostasy [START_REF] Rouby | Long term stratigraphic evolution of Atlantic-type passive margins; a numerical approach of interactions between surface processes, flexural isostasy and 3D thermal subsidence[END_REF]. The erosion of CHAPTER 5 :ESTIMATION OF ACCUMULATED SEDIMENTARY VOLUMES ON THE AFRICAN EQUATORIAL ATLANTIC MARGIN 151 rift shoulders takes usually less than 10 Ma [START_REF] Rouby | Long term stratigraphic evolution of Atlantic-type passive margins; a numerical approach of interactions between surface processes, flexural isostasy and 3D thermal subsidence[END_REF], which could explain the decrease of sedimentary flux during the Turonian-Santonian. The Maastrichtian peak maybe related to a relief reorganization triggered by a tectonic event along the margin. Indeed, a Santonian tectonic inversion affected the Benue Trough, which seems to have been reactivated during the Maastrichtian [START_REF] Benkhelil | The origin and evolution of the Cretaceous Benue Trough (Nigeria)[END_REF][START_REF] Benkhelil | The Benue Trough; wrench-fault related basin on the border of the Equatorial Atlantic[END_REF]. The Santonian event seems to be a continental-scale tectonic event, which affected the margin by producing uplift. This would be attested by a forced regression wedge of Santonian age followed by Maastrichtian progradation in Eastern Ivory Coast (Chapter 4). The reason why no increase in sedimentary flux is observed during the Campanian following the Santonian event is unclear.

Cenozoic Sedimentary Budget

During the Cenozoic, higher variations in accumulated volumes and accumulation rates with higher frequency are recorded in Ivory Coast and Ghana-Benin thanks to the higher time resolution than during the Late Cretaceous. In Ivory Coast, the trends in volumes and rates are similar for the extrapolated and non-extrapolated cross-sections (Figure 56789). Accumulation decreases during the Paleocene-Eocene (from about 6.8 to 3.1 x10 12 m 3 /Ma), increased in the Lower Oligocene (about 1.8x10 13 m 3 /Ma), decreased again from the Early Oligocene to the Late Miocene before a second peak (about 1.2x10 13 m 3 /Ma) in the Plio-Quaternary. The trends of volumes and rates are different in Ghana-Benin with a single peak in accumulated volumes (about 3.5x10 13 m 3 /Ma) and rates (about 5.5x10 12 m 3 /Ma) during the Late Miocene assuming extrapolation would not modify these trends.

The accumulation peak during the Early Oligocene could be more significant, as Oligocene erosion might have reworked a large quantity of older sediments [START_REF] Huyghe | Forçage des liens source-marge au Cénozoïque (marge Bénin-Sénégal[END_REF]. It may be related to the major drainage reorganization observed onshore during the Late Eocene-Early Oligocene, when the Niger River and the Volta significantly increased their catchment areas [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. Meanwhile, the Hoggar Shield was uplifted and submitted to erosion (Ye et al., submitted).

The absence of Early Oligocene accumulation peak in Ghana-Benin could be attributed to the reworking of Lower Oligocene sediments by later erosions (from Oligocene until Late Miocene)

producing a large number of voluminous mass-transport deposits (MDTs: slumps, debris flows, etc., [START_REF] Huyghe | Forçage des liens source-marge au Cénozoïque (marge Bénin-Sénégal[END_REF]. The Late Miocene peak could therefore be artificial because it could result from such reworkings. Contourites were also recognized [START_REF] Huyghe | Forçage des liens source-marge au Cénozoïque (marge Bénin-Sénégal[END_REF] that could have brought sediments from the Southern African margins. The role of MDTs and contourites should be further investigated, in order to reduce the uncertainties on sedimentary volume estimation.

Conclusion

We quantified the accumulated solid volumes and the accumulation rates of terrigenous sediments preserved in the Sierra Leone-Liberia, Ivory Coast and Ghana-Benin basins of the African Equatorial margin. The methodology is based on interpolation of regional cross-sections and multiple corrections (carbonates, remaining porosity). Accumulation histories show two peaks during the Late Cretaceous: a Cenomanian peak, which could be explained by erosion of rift shoulders during the immediate post-rift, and a Maastrichtian peak that could be related to a platescale inversion event. During the Cenozoic, an Early Oligocene accumulation peak could be associated with the onshore drainage reorganization due to the Hoggar uplift. However, multiple

Oligocene-Late Miocene erosional events may have disturbed the pre-Late Oligocene sedimentary record by reworking by mass-transport deposits.

Despite the uncertainties, these accumulation histories (Sink) form the basis for our 'sourceto-sink' analysis along the African Equatorial Atlantic margin. Their comparison with onshore continental denudation histories and relief changes (Source) will be carried out bellow (Chapter 6). [START_REF] Kouamelan | Géochronologie et géochimie des formations archéennes et protérozoïques de la dorsale de Man de Côte d'Ivoire; implications pour la transition archéen-protérozoïque[END_REF].

Analyses and dating of these samples were done by D. Webster (AHe dating) and M. Wildman The uranium concentration is measured by counting tracks that are induced in specimen by irradiation with thermal neutrons in a nuclear reactor. The induced tracks are principally related to the fission of 235 U which has a large thermal-neutron capture cross-section [START_REF] Donelick | Apatite fission-track analysis[END_REF].

As the ratio of 238 U to 235 U is constant in natural minerals, 238 U content can be deduced.

The age equation is expressed as following [START_REF] Naeser | Fission track annealing in apatite and sphene[END_REF][START_REF] Fleischer | Nuclear tracks in solids. Principles and Applications[END_REF]: As zeta (ȗ) is equivalent to ఙூ , equation ( 1) is simplified as:

ݐ ൌ ଵ ఒ ವ ሺͳ ݃ ఒ ವ థఙூ ఒ ఘ ೞ ఘ ) (1)
ݐ ൌ ଵ ఒ ವ ሺͳ ݃Ƀɏ ୢ ఘ ೞ ఘ ) (2)
Each fission track worker should have his own zeta (ȗ) parameter by averaging over many separate measurements on age standards.

c) Procedure and Technique

Two procedures are commonly used for determining a fission track age: the population and external detector methods. The population method measures the spontaneous and induced track densities separately on two aliquots from the same sample based on an assumption of uniform uranium distribution within grains from the same sample. However, the external detector method, which is adopted in this study, avoids this assumption and dates grains individually from one aliquot (Figure 6-2). The surface of a given apatite mineral is firstly grinded and polished, and then etched by 5N HNO3 for around 20s under 20°C. After the etching treatment, surface fission tracks which intersect the etched surface are revealed. The confined tracks can also be reached by the etchant through surface tracks, cleavage or fracture. An external detector, such as a sheet of mica is put on this surface and then set to a nuclear reactor. The irradiation induces fission events in 235 U.

They are registered in the mica by the formation of induced fission tracks. The mica is etched afterward to reveal the induced tracks. In the end, one grain mount is obtained for measuring spontaneous track density (ȡs) and another one for estimating induced track density (ȡi). The fission track age for each single grain is then obtained by using the Equation ( 2) above.

Annealing and Fission Track Length

Apatite fission track ages have been found decreasing at depth with a temperature more than 100°C in deep drill holes. In fact, spontaneous fission tracks remain stable only at low temperature. Partial annealing happens when temperature increases, which shortens the length of fission track or removes totally the tracks. A temperature range over which annealing occurs is defined as 'partial annealing zone (PAZ)'. For apatite, PAZ ranges from 60° to 110±10°C with an uncertainty of 10°C according to the annealing model [START_REF] Gallagher | Fission track analysis and its applications to geological problems[END_REF].

Track lengths are measured directly using a digitalized tablet and a microscope stage graticule calibrated by a micrometer. Only confined tracks entirely below and parallel to the etched surface are measured, which give a reliable real length distribution. The identification of confined track is possible by combining reflected and transmission light of the TEM. The track length data are then reported in a histogram with mean value, standard deviation and other parameters, such the angle between tracks and crystallographic c-axis. Because the etching and annealing processes are both anisotropic and controlled by crystal's crystallographic structure. Annealing is slower and the etching faster in the direction of the crystal's crystallographic c-axis. A correction of track length is proposed by some authors by using the angle to the c-axes of each track to deduce a supposed track length parallel to the c-axes, which is debatable for some other authors [START_REF] Donelick | Variability of apatite fission-track annealing kinetics: II[END_REF][START_REF] Ketcham | Observations on the relationship between crystallographic orientation and biasing in apatite fission-track measurements[END_REF].

Reduction on track length is controlled by temperature as well as time. A kinetic model of fission track annealing is firstly proposed by [START_REF] Laslett | Thermal annealing of fission tracks in apatite 2. A quantitative analysis[END_REF] on which subsequently published models are based. It describes a fanning Arrhenius plot with straight lines of equal track length reduction formed in a plot of log of time against inverse absolute temperature. All the lines converge to a point at infinite temperature because the slope increases with higher degree of annealing.

The composition of apatite also controls the annealing process, especially the Cl, F and OH contents. For example, apatite richer in Cl is more resistant to annealing than F-apatite. So they give longer fission track lengths.

Interpretation of Fission Track Data in Terms of Thermal History

Fission track ages can not be used without a combination with track-length data to interpret the thermal history of samples. If an apatite crystal experiences a continuous heating, all fission tracks formed at different times will be shortened to the almost same degree (Figure 6 6-3c). In an ideal case, a finite spread of length is expected. If the tracks formed after a heating experienced a cooling afterwards, the tracklength distribution is typically bimodal (Figure 6-3d). We can not directly relate the fission track age to the timing to cooling.

Limitation and Uncertainty of the Method

The limitation of the AFT method is that only a recent thermal history after the last passage through PAZ is recorded. No information for the history prior to the onset of cooling can be obtained with precision by this method. Uncertainty persists due to the counting of the track numbers and the length measurement. The uranium concentration should not be too low or too high for a countable number of spontaneous fission tracks to accumulate. The possible uneven distribution of uranium in the specimen is also a source of error. Apatite (U-Th-Sm)/He dating method is based on the alpha decay of uranium, thorium isotopes and to some extent, samarium isotopes. The number of helium nuclei (or Į particle) accumulated in apatite grain is a function of uranium, thorium and samarium content and time as below:

4 He = 8* 238 U (e Ȝ 1 t -1) +7* 235 U (e Ȝ 2 t -1) +6* 232 Th (e Ȝ 3 t -1) + 147 Sm (e Ȝ 4 t -1)

Where 4 He, 238 U, 235 U, 232 Th, 47 Sm are isotope contents, Ȝ1,2,3,4 are decay constants.

Assuming that all produced helium nucleus are retained in the crystal and no other extraneous source of helium (e.g. inclusions of other minerals), an AHe age can be obtained by measuring the U, Th and Sm amounts.

b) Techniques and procedures

The adopted procedure for measuring He, U, Th and Sm concentrations involves firstly a careful selection of apatite grains (size, shape and inclusion free). Afterwards, helium extraction is processed using a Quadrupole mass spectrometer. Apatite crystals are degassed inside a platinum capsule by heating with a laser. The helium gas is purified by passing through liquid nitrogen before going into the mass spectrometer where helium concentration is measured. A calibration is made by repeat measurement of a 4 He standard throughout the analysis.

After helium extraction, the apatite crystals are dissolved and spiked with a solution with a known concentration of 235 U, 230 Th and 149 Sm. Samples are then analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The concentrations of 238 U, 232 Th and 147 Sm can be obtained and calibrated by a known 238 U.

Helium Diffusion and Radiation Damage

What makes (U-Th-Sm)/He dating a thermochronometer is the fact that He nuclei experiences thermal diffusion within apatite through time. In fact, helium nuclei can only be retained within the crystal below a certain temperature and the diffusive loss of He decreases CHAPTER 6 :CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 165 through a cooling trajectory. A theoretical partial retention zone (PRZ) is defined as a temperature range where the retention of helium begins and increases with temperature, which has a similar fashion of the partial annealing zone (PAZ) for AFT dating. The PRZ was estimated to be a temperature range of ~ 40 to 75± 5 °C by early studies of He diffusion [START_REF] Farley | Helium diffusion from apatite: General behavior as illustrated by Durango fluorapatite[END_REF]. This makes the understanding of the thermal history of the very upper part of the crust (1-3 km) possible.

However, recent investigation revealed that radiation damages caused by alpha recoil had influence on diffusion by increasing the retention of helium within apatite. Alpha recoil is in return controlled by the effective uranium concentration ([eU]=[U]+0.24*[Th]). The higher effective uranium concentration creates more radiation damages, then increases the temperature range of PRZ and the measured age will be older. However if effective uranium concentration is very significant, He diffusion can be promoted [START_REF] Shuster | The influence of natural radiation damage on helium diffusion kinetics in apatite[END_REF][START_REF] Flowers | Apatite (U-Th)/He thermochronometry using a radiation damage accumulation and annealing model[END_REF][START_REF] Gautheron | Effect of alpha damage annealing on apatite (U-Th)/He thermochronology[END_REF].

Alpha-ejection

In addition to diffusion of helium, a process of alpha-ejection was discovered to increase the loss of helium in the crystal. In reality, when Į particles are emitted from their parent isotope, they possess enough energy to travel up to ~ 20 μm before coming to rest, called 'stopping distance' (R) [START_REF] Farley | The effects of long alpha-stopping distances on (U-Th)/He ages[END_REF]. As a result, a proportion of alpha particles may be lost from the crystal when the ejection happens within 20 μm from the crystal edge (Figure 6-4). When U and Th rich minerals (e.g. zircon, titanite, monazite) are aside or inside of the apatite grain, long stopping distance of Į-particles may result in implantation or inclusion of alpha particles into the apatite (Figure 6-4). A correction factor (Ft) is proposed to be used for calculation of AHe ages, which depends largely on the grain size. But this correction is debated when Į-decay comes to interplay with diffusion and it's considered to over-correct ages in case of significant diffusion [START_REF] Gautheron | Accounting for long alpha particle stopping distances in (U-Th-Sm)/He geochronology; 3D modeling of diffusion, zoning, implantation, and abrasion[END_REF].

Limitation and Uncertainties

Consequently, it is difficult to define sets of kinetic parameters for the AHe system by taking into account all factors, such as composition, crystal size, radiation damage and zonation of U, Th and Sm. Several kinetic models of helium diffusion have been proposed with differently defined relations between parameters [START_REF] Shuster | The influence of natural radiation damage on helium diffusion kinetics in apatite[END_REF][START_REF] Flowers | Apatite (U-Th)/He thermochronometry using a radiation damage accumulation and annealing model[END_REF][START_REF] Gautheron | Effect of alpha damage annealing on apatite (U-Th)/He thermochronology[END_REF]. Uncertainty still exists within AHe analysis due to these aspects.

Power of Combination of Two Methods

Since two methods cover different ranges of temperature (60-110°C for AFTA and 40-80°C

for AHe, Figure 6-5), AHe dating can only provide information about the very recent thermal history of crystal, while AFTA can constraint the older thermal history with cooling rate revealed by the track-length distribution. So the combination of both methods allows a better understanding of the thermal history of samples and then provide more precise information on denudation histories.

CHAPTER 6 :CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 167 palaeo-PAZ and palaeo-PRZ [START_REF] Wildman | Reassessing the structural and geomorphic evolution of a "classic" Atlantic type passive margin: an integrated study of the Namaqualand sector of the South African continental margin[END_REF].

In the case of complex episodic cooling, the combination of two methods appears to be absolutely necessary. Imaging a sample experienced two different cooling episodes (Figure 6-6),

AFTA or AHe dating alone can only provide a single old or young age with a simple cooling path, although both results fulfill the separate thermochronological data. But the true thermal history can only be obtained by combining both AFTA and AHe methods.

The combination of both methods is used widely in tectonically stable cratonic areas. In fact, in tectonically active domains, such as mountain belts, crystals pass through the PAZ or PRZ with relatively higher velocity. We obtain often similar AFT and AHe ages. In cratonic areas, the CHAPTER 6 :CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 168 cooling is much slower. This has been revealed by the fission track length distribution with a low mean length value (from 11 to 13 ȝm) and a high standard deviation. We expect a bigger difference of AFT and AHe ages in cratonic domains and to have more precision on possible cooling rate by combing the two sets of ages. However AFT and AHe ages are sometimes difficult to be interpreted.

For example, AHe ages are found in some cases older than AFT ages of the same samples, while we expect older AFT ages according to the higher AFTA temperature range. This incoherence is explained by some authors as a result of radiation damage related to a high eU concentration [START_REF] Shuster | The influence of natural radiation damage on helium diffusion kinetics in apatite[END_REF][START_REF] Flowers | Apatite (U-Th)/He thermochronometry using a radiation damage accumulation and annealing model[END_REF][START_REF] Gautheron | Effect of alpha damage annealing on apatite (U-Th)/He thermochronology[END_REF]. This means radiation damage could act as a retaining trap and result in older AHe age. But when eU concentration goes beyond a certain level, radiation damage may in reverse make diffusion more efficient. A more explicit radiation damage related diffusion model for AHe dating is still demanded. HeFTy (Leprêtre, 2015).

CHAPTER 6 :CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 169

TS2P Sampling

Earlier low-temperature thermochonological analysis in West Africa were carried out on samples from the Reguibat and Hoggar Shield (Cavellec, 2006;Rougier et al., 2013;Leprêtre, 2015;English et al., 2016, Figure 6-7). Only one study was undertaken on the Leo-Man Shied in Burkina Faso (Gunnell, 2003, Figure 6-7), far from the Equatorial Atlantic margin. Other studies were made on samples from ODP Leg 159 (Clift et al., 1998;Bouillin et al., 1998;Bigot-Cormier et al., 2005, Figure 6-7), in order to investigate vertical movements of the Ivory Coast-Ghana marginal ridge.

No study on the Mesozoic denudation history of the basement along the Equatorial Atlantic margin exist yet. The TS2P project allowed sampling the margin from Guinea to Benin for the purpose of low-temperature thermochronological analysis (AFTA and AHe dating, Figure 67). Three transects were established from West to East, in Guinea, Ivory Coast and Benin (Figure 67). They aimed to reveal the thermal and denudation history of three major segments of the margin, which also correspond to long-lived drainage basins whose Cenozoic evolution was investigated in details [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF].

Guinea Transect

Ivory Coast Transect

The Ivory Coast transect consists of 13 samples given by A. Kouamelan Ma) was yielded again by the northernmost sample (BN-6), which could be associated with the independent thermal history of the Gao rift that is nearby (see the paleogeographic study). However, no clear correlation of AFT ages with elevation is observed (Figure 6-12). Mean track lengths range from 10.3±0.7 to 13.1±0.1 μm with a majority under 12.5 μm. Cooling events were a priori slow in Ivory Coast, as annealing of fission tracks was more intense. AFT and track length data were interpolated on a map (Figure 6-15). Additional AFT data published in Burkina Faso (Gunnell, 2003) were also incorporated. The resulting distribution of ages shows a spatial variability from North to South, and from West to East. Young AFT Early Cretaceous ages (100-150 Ma) are concentrated mostly along a coastal corridor of c. 400 km wide.

Older AFT ages (> 150 Ma) are found far on the Northeast, and are also presented at local spots in Guinea and Ivory Coast. The distribution of MTLs is rather homogenous with a value of c. 13 μm.

Short MTLs (< 12μm) were found only in Benin on the East, but the longest MTLs were yielded in Guinea. The fact that the southernmost Benin sample yielded shortest MTLs could be related to its independent uplift and burial history due to its location within the Dahomey Embayment.

Overall, the whole dataset supports a dominant phase of crustal cooling for the coastal corridor during the Early Cretaceous, which is the syn-rift stage of the Equatorial Atlantic margin (140 -107 Ma, Figure 3-6 and Figure 34567). It also highlights pontentially complex spatial and temporal cooling patterns across the study area with samples recording differentiate thermal events.

AHe Ages

Not all samples have successfully yielded an AHe age, due to sample quality (Appendix 7).

Single grains of one sample can yield ages with a great dispersion, which implies the influence of different chemical and structural characteristics of each grain, such as eU and grain size (R*).

Obtained mean sample AHe ages are in agreement with AFT ages in general, ranging from 282.2 to 51.7 Ma (Appendix 7). Oldest AHe ages were also obtained in Benin, where they are comparable to the AFT ages. Several samples yielded AHe ages exceeding their corresponding AFT ages (BN12, BN18, SA-14, MK-64 and GN02). It is common in cratonic areas where effective uranium content is high and radiation damage effect is important. The relationships between the accumulation of radiation defects and alpha trapping are still unclear, considering the influence of grain radius and fragmented grains in addition. In general, samples do not show any positive age-R* and age-eU relationships. Overcorrection of AHe age using a single alpha-correction may also contribute to the overlap of AHe ages on AFT ages [START_REF] Wildman | The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U-Th-Sm)/He thermochronology: Tectonics[END_REF]. Therefore, the AHe data cannot be interpreted based only on the observed ages.

AFT and AHe ages do not essentially indicate a specific event. They need to be interpreted, taking into account other parameters (e.g., track length, eU content). We can only assess the thermal histories by using inverse modeling

6.5.

Thermal History Modeling 6.5.1. Approach: QTQt

In order to generate thermal history and quantify surface processes (e.g. erosion and burial) that fit the observed data, inverse modelling is usually performed on specific software (e.g. QTQt,

HeFTy). In this study, QTQt, a Bayesian transdimensional approach to data inversion is used [START_REF] Gallagher | Transdimensional inverse thermal history modeling for quantitative thermochronology[END_REF].

A fundamental input for the modelling is a theoretical annealing or diffusion model defining how AFT or AHe thermochronometer evolves as a function of temperature and time. For the AFT, the multi-kinetic fission track annealing model of [START_REF] Ketcham | Improved modeling of fission-track annealing in apatite[END_REF] is applied in QTQt, which accounts for the differences in annealing rate in apatite grains with different chemistry (e.g. F and

Cl content) and different angles of tracks to the c-axis. The Durango diffusion model of Farley ( 2000) is adopted for AHe data inversion. It defines the activation energy of alpha production for the U, Th and Sm decay, alpha stopping distances and thermal diffusivity for grains with a spherical approximation. Additional different radiation damage annealing models can be assessed separately [START_REF] Shuster | The influence of natural radiation damage on helium diffusion kinetics in apatite[END_REF][START_REF] Flowers | Apatite (U-Th)/He thermochronometry using a radiation damage accumulation and annealing model[END_REF][START_REF] Gautheron | Effect of alpha damage annealing on apatite (U-Th)/He thermochronology[END_REF].

The modelling approach of QTQt uses Bayesian transdimensional Markov Chain Monte Carlo (MCMC) method. It defines a wide range of possible thermal history models to be considered as prior information (a limited range of temperature and timescale). Sampling is based the MCMC approach through which the current model is perturbed to generate a proposed model which is then accepted or rejected according to its likelihood fitting the observed model [START_REF] Gallagher | Transdimensional inverse thermal history modeling for quantitative thermochronology[END_REF] The main advantage of the Bayesian approach is that the number of T-t points is treated as unknown parameter and models with fewer T-t points are preferred during sampling. This avoids over complex thermal history model and propose simple models which fit adequately to the observed data.

The MCMC sampling should be run for a minimum of c. 200.000 iterations and all tested thermal history models, each with a related posterior probability of fitting the observed data are collected to produce a summary probability distribution map of temperature-time. Then the expected model can be determined by the mean thermal history model weighted for its posterior probability. The maximum likelihood model is considered as the model which fits the observed data best, but it is often too complicated to be justified by geological constraints. Therefore, the expected model tends to provide the most suitable insight to thermal history.

Modeling Results of TS2P Samples

The measured data (AFT and AHe data) of each sample were preferentially modelled jointly to provide better constraints for possible T°C/t models to be tested. The AHe data help constraining the thermal history through lower temperatures (40 -80 °C), whereas the AFT data constrain that through higher temperatures (60 -110 °C). Integrating both AFT and AHe data is crucial to define distinct transition in cooling style over time.

Other geological constraints (e.g. deposition age for sedimentary rocks, overlying volcanic or sedimentary rock, age of erosional surfaces) were used as constraints in modelling to predict a more robust thermal history (Appendix 8 to 10).

Guinea Transect

Data from samples in Ivory Coast were inverted using the procedure above. Only the AFT data and geological constraints were used, because the AHe data are limited in Guinea. The onset of cooling for resulting thermal histories occurs within three time periods (Figure 6-16): Early ). The cooling rate is slow (0.5 to 0.8 °C/Myr) which is common in cratonic domains.

The temperature at the beginning of cooling should be more than 120 °C. Because this region was heated by the CAMP event, thermal history older than 200 Ma should not be preserved and so is not considered here.

Ivory Coast Transect

Modelling results of 9 samples projected on an N-trending transect of Ivory Coast were presented below. They were modelled with AFT and available AHe data, as well as geological constraints where available (Appendix 9). Samples close to each other (<50 km distance) were modelled together. In general, the onset of cooling occurs within one of three time periods: Early Jurassic (190 -170 Ma), Mid-Late Jurassic (170 -150 Ma), Early Cretaceous (140-130 Ma).

Different cooling rates were recorded within these time intervals models, which also indicate spatial variabilities in the regional cooling pattern. The rifting affects the onshore continent at a distance of less than 100 km from the coastline. Wildman.

Benin Transect

Samples of the Benin transect were also modelled with both AFT and AHe data, and geological constraints. Considering the regional geology along the Benin transect (see above)

samples were modelled with or without reheating permission according to the sample location.

Samples near the coastal basin (BN-18 and BN-1) were modelled with reheating permitted due to their potential burial in the embayment, as well as samples close to the Kandi/Iullemmeden basin (BN-6, -7, -8, -9, Figure 6-18). Only interior samples far from both basins were modelled with no reheating permitted. Adjacent samples sharing the same geological constraints and have similar thermochronological data were modelled together.

Exported Volumes

Interpolation Procedure and Uncertainty Assessment

In order to calculate exported volumes of eroded materials, we interpolated the incremental denudation values of each TS2P samples, as well as the AFTA data of Gunnell (2003) in Burkina

Faso. An area was defined for interpolation containing all the data points, and its Southern and Western boundaries coincide with the coastline. A triangulated surface was constructed for each time interval using the Gocad software. The resolution of the surface was adjusted by controlling the size of the triangles. Values of denudated volumes were then automatically obtained from each surface.

In order to assess the uncertainties associated with the interpolation procedure, a first set of surfaces was created with a free boundary, which allows any values at the boundary (Figure 6

Denudation Maps and Volumes

The denudation maps show the distribution of erosion in time and space. Despite the differences in values between the maximum and minimum denudation maps (Figure 6 Ma (2.1 to 1.1x10 13 m 3 /Ma). A small peak in volumetric denudation rate (2.1x10 13 m 3 /Ma) occurred during the Valanginian-Aptian (140 -120 Ma), followed by a slow decrease in rate until the Miocene (20 Ma). Regionally averaged denudation rates show a range of 7 to 16 m/Ma through time, which is typical for cratonic domains (e.g., [START_REF] Beauvais | Modes, tempo, and spatial variability of Cenozoic cratonic denudation; the West African example[END_REF]. Instead of showing major denudation pulses (several kms) due to rifting and/or later tectonic events like that recorded by Southern Africa in the Late Cretaceous (e.g., [START_REF] Tinker | Mesozoic exhumation of the southern Cape, South Africa, quantified using apatite fission-track thermochronology[END_REF], the Equatorial margin of Africa has recorded slow denudation typical of cratonic domains even though rifting may be detected in its Early Cretaceous denudation pattern. This chapter presents the preliminary results of a source-to-sink analysis based on denudated (Chapter 6) and accumulated (Chapter 5) volumes and rates. The first-order Meso-Cenozoic changes in sedimentary fluxes and paleo-drainage system in West Africa are first discussed, as well as their implications for the understanding the Equatorial African sediment routing system. In a second section, vertical displacements of the margin induced by these sedimentary transfers are calculated for the Ivory Coast case, where the behavior of both the divergent and transform margin segments were simulated.

Source-to-Sink Sediment Budget

We compared the denudated and accumulated sediment budgets from the Late Cretaceous to the Cenozoic (100-0 Ma). The Middle Eocene-Quaternary (45-0 Ma) source-to-sink analysis is based on the accumulated volumes estimated in the course of this work (Chapter 5) and the eroded volumes of [START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF], which are based on the subtraction of dated relict lateritic landsurfaces.

We used the denuded volumes retrieved from low-temperature thermochronological analysis (Chapter 6) and the accumulated volumes (Chapter 5) for the Late Cretaceous -Early Eocene (100-45 Ma) source-to-sink analysis. The Early Cretaceous syn-rift source-to-sink sediment budget was not interpreted because of the difficulty / impossibility to estimate syn-rift sediment volumes from the 2D seismic data. Moreover, some of the syn-rift depocenters are now located offshore the conjugate margin of South America, and the contribution of the South American continental surface to those depocenters must be significant.

Middle Eocene -Quaternary (45 -0 Ma)

Clastic fluxes are first-order data to understand the transfer of eroded materials from their source to their basin sink. Post-Middle Eocene denudation history (45 -0 Ma) of West Africa was well constrained by relictual lateritic landscapes at a much higher resolution than the thermochronological data [START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF][START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]). Three regional-scale paleosurfaces were reconstructed by interpolation: the S1 (45 Ma), S2 (24 Ma) and S3 (11 Ma) CHAPTER 7 :OUTLINES OF A SOURCE-TO-SINK ANALYSIS, IMPLICATIONS FOR VERTICAL DISPLACEMENTS OF THE MARGIN 198 surfaces [START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF]. Denudation maps for three intervals were obtained by subtracting successive paleosurfaces and the modern topography. Drainage divides were defined on the paleolandsurface geometries that had been corrected for the isostatic flexural deformation they have undergone since their abandonment as a consequence of erosional discharges and sedimentation charges [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. A major shift in the drainage divide was documented between 34 and 29 Ma (after the abandonment of the S1 surface at 45 Ma and that of the S2 surface at 24 Ma) as a far-field effect of the growth of the Hoogar hot spot swell [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF] (Figure 7-1). At 29-24 Ma, the main divides of the sub region were established [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. The quantification of eroded volumes was carried out for three major drainage areas contributing to the Equatorial margin (i.e., Short Atlantic drains, Long Atlantic drains, and Niger catchment), taking into account the uncertainties on drainage divides locations (Grimaud et al.,in prep.,. Exported volumes were corrected by subtracting the Cenozoic volumes preserved in intracontinental basins to the eroded volumes. In the end, clastic exported volumes were extracted from exported volumes assuming a mean regolith porosity of 25%, as mostly regolith, as opposed to fresh bedrock, is the clastic material being provided to the river systems [START_REF] Beauvais | Modes, tempo, and spatial variability of Cenozoic cratonic denudation; the West African example[END_REF][START_REF] Grimaud | Neogene cratonic erosion fluxes and landform evolution processes from regional regolith mapping (Burkina Faso[END_REF]Grimaud et al., in prep.) Overall, the sub region exported 928 10 3 km 3 of clastic sediments to the Equatorial Atlantic Ocean during the 45 -0 Ma interval. More volumes were exported from the Niger catchment than the Long Atlantic drains (Table 7-1). The least of volumes were exported from the Short Atlantic drains, which represent the smallest contributing area. At first-order, exported rates increased in all basins between 45 -24 Ma and 24 -11 Ma, as contributing areas increased in size as a consequence of drainage reorganization. A decrease in exportation occurred for the 11-0 Ma period.

We compared the export rates with non-extrapolated accumulation rates measured in the nearby Equatorial basins (Chapter 5) and the Niger delta (Figure 7-1, Grimaud et al., in prep.). The reason why non-extrapolated accumulation rates were used is that the extrapolated accumulation rates could not be obtaiend in the Ghana-Benin basin (Figure 5-9), where the contribution of the Niger Delta is significant and should be distinguished. Overall, they fall within the same order of magnitude for each independent source-to-sink system roughly corresponding to a margin segment (Figure 7-1 and Table 7-1). The sediment budget is fairly well balanced during the 45 -24 Ma and CHAPTER 7 :OUTLINES OF A SOURCE-TO-SINK ANALYSIS, IMPLICATIONS FOR VERTICAL DISPLACEMENTS OF THE MARGIN 199 and their sink basins, and between the Niger catchment and its delta (Figure 7-1 and Table 7-1).

However, the accumulation rate largely exceeds the export rate during the 11 -0 Ma interval for these two systems. Different trends are observed for the Short Atlantic drains and the Sierra Leone-Liberia basin, as only the bulk (i.e., 45-0 Ma) accumulation rate was obtained (Figure 7-1 and Table 7-1). The total exported volume by Short Atlantic drains was estimated to be 111 ± 15 l0 3 km 3 , which is comparable to the accumulated volume of 148 ± 31 10 3 km 3 . Long Atlantic drains, the Short Atlantic drains and the Niger catchment with their corresponding sink basins, Figure 7-1).

Late Cretaceous -Early Eocene (100 -45 Ma)

The denudation rates deduced from the thermochronology (Chapter 6) and accumulation rates determined offshore (Chapter 5) allow the Late Cretaceous-Early Eocene (100 -45 Ma) overall sediment budget between the African Equatorial margin and its hinterland (Figure 7-2). The paleodrainage(s) for that time interval remains unknow due to the limitation of the thermochronological method and to the lack of paleolandscape remnants of that age. The contributing area may be different from that covered by the thermochronological data. However, the paleo-maps (Figure 3 The order of magnitude is the same for the total denudation and the cumulated accumulation on the whole Equatorial Atlantic margin (Table 7-2). A total volume of 6.8 ± 1.7 10 5 km 3 was denuded in West Africa during 100 -45 Ma, of which 4.5 ± 1.0 10 5 km 3 were eroded during the Late Cretaceous (100 -65 Ma). The total clastic volume accumulated in the Equatorial Atlantic basins was up to 8.1 ± 1.9 10 5 km 3 , 6.9 ± 1.7 10 5 km 3 of which were deposited during the Late

Interpretation

Overall, the clastic sedimentary volumes are well-balanced for the 45 -11 Ma time interval between West African drainage systems and their sink basins. The higher values in exported and accumulated volumes during the 24 -11 Ma interval would support drainage reorganization before 24 Ma that led to dramatic increase in the size of the Niger and long Atlantic drains' catchments [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. Since that reorganization, the Niger catchment incorporated the uplifting Hoggar Shield. Large quantities of sediments were then exported to the Niger delta. However, the higher accumulation rate during the 11-0 Ma interval in the Niger Delta and the Equatorial Atlantic is not supported by our export rate data. One explanation is the temporary storage of the previously eroded sediments in the intracontinental basins (e.g., Iullemmeden basin), that were exported only after 11 Ma (Grimaud et al., in prep.). In fact, less sediments were accumulated on the margin than exported during the 24 -11 Ma interval for the Niger catchment and the Long Atlantic drains. The budget could therefore be better balanced for the 11 -0 Ma interval as a consequence of the tapping of Paleogene (pre-24 Ma) sediments that were stored in the Iullemmeden basin (probably more than 10 5 km 3 ). Lateral currents can also have brought sediments (i.e., contourites) from nearby margins, which would further explain the excess. Large quantities of contourites are indeed

Approach

We used the numerical Flex3D model of Braun et al., 2013, which In this work, we first defined a 2D stretched geometry (hm and hc) of the lithosphere inspired from offshore seismic profiles and African crustal and lithospheric thickness model (Bajolet et al., in prep.). Densities of the continental and oceanic crusts are referred to published geophysical data along the Atlantic Equatorial margin [START_REF] Edwards | Synthesis of the crustal structure of the transform continental margin off Ghana, northern Gulf of Guinea[END_REF][START_REF] Sage | Crustal structure of the continent-ocean transition off the Cote d'Ivoire-Ghana transform margin; implications for thermal exchanges across the palaeotransform boundary[END_REF]. By defining a reference crustal thickness (h0r, with this thickness, the surface of the crust is at the altitude of 0 m) of 29 km, a topo-bathymetric profile for the stretched lithosphere is reproduced in Flex3D, in response to the isostatic flexure of the lithosphere. In order to calculate the vertical displacements resulting from onshore denudation (d) and/or offshore sedimentary loading (s), we defined the above stretched geometry of the lithosphere as a reference, and a new geometry of the lithosphere is obtained by subtracting the denudation from the continental crust thickness of the reference and/or adding sedimentary loading on the reference oceanic crust thickness. A new topographic CHAPTER 7 :OUTLINES OF A SOURCE-TO-SINK ANALYSIS, IMPLICATIONS FOR VERTICAL DISPLACEMENTS OF THE MARGIN 205 and bathymetric profile of this geometry is then obtained and compared with that of the reference case. The difference between these two topographic and the bathymetric profiles (¨h) gives the value of vertical movements (U), using the relations: U = d -¨h and/or U = s + ¨h.

In doing so, no surface processes were incorporated, neither the variation of the EET in time and in space. The limitation of this model is that the difference between continental and oceanic crusts is only expressed by different densities. The thermal evolution of the oceanic crust and its impact on the vertical movements were not taken into account.

Model Setting

The thermochronological transect of Ivory Coast was used for inland denudation history.

Two seismic profiles crossing the transform and the divergent parts of the margin, were used for sedimentary loading estimation (Figure 7-3). The transform and divergent margins with distinguishable necking widths (140 km VS 40 km) were modelled separately. For each margin, 6

cases were tested (Table 7-3):

(1) Denudation only during 140 -0 Ma;

(2) Denudation and sedimentary loading during 140 -0 Ma inverval;

(3) Averaged Denudation and sedimentary loading during 140 -0 Ma inverval;

(4) Denudation and sedimentary loading during 140 -100 Ma inverval;

(5) Denudation and sedimentary loading during 100 -65 Ma inverval;

Interpretation

Sedimentary loading does not influence the onshore denudation-induced uplift pattern.

Indeed, the denudation only-induced inland uplift profile (yellow line,

Conclusion

New denudation and accumulation data acquired in this work allowed for a first-order source-to-sink study of the paired shield-margin system of Northwestern Africa along its Equatorial margin since the Early Mesozoic. Earlier works on Cenozoic denudation history and drainage systems [START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF][START_REF] Grimaud | Neogene cratonic erosion fluxes and landform evolution processes from regional regolith mapping (Burkina Faso[END_REF][START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF] were used to be compared to newly acquired Cenozoic accumulation history in the Equatorial Atlantic basins. Three source-tosink systems related to three major catchments show similar trends of denudation and accumulation rates. The Late Oligocene reorganization of drainage systems was well recorded in the offshore basins by an increase in sedimentary input, which in turn confirms the paleo-drainage configuration and reorganization [START_REF] Chardon | Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River: Geochemistry[END_REF]. Mesozoic sediment budgets were evaluated at the scale of NW Africa and its Equatorial margin on the basis of an onshore thermochronological study and newly acquired offshore sediment accumulation history. The total sedimentary volumes were well-balanced overall for the Late Cretaceous, post-rift history of the margin, within uncertainties. A slight excess of accumulation compared to erosion during the Late Cretaceous and since the Late Miocene reflects the complexities of source-to-sink sedimentary routing systems. Among those complexities, transient intracratonic storage of sediments issued from marginal upwarp erosion, and remobilization of older sediments on the margin is the most significant.

Source-to-sink sediment transfers in West Africa induced significant vertical movements due to flexural isostasy of the lithosphere. Onshore uplifts of ca. 1 km and maximum subsidence of 4 to 5 km may be produced, with a comparable impact on divergent or transform segments of the margin. Onshore uplift pattern is solely controlled by denudation, and the long-term thermal and sedimentary history of the adjacent margin did not influence inland vertical movement except for a narrow (2 km wide) coastal strip of higher uplift and denudation produced only during rifting. Rb-Sr [START_REF] Halliday | TraceͲelement fractionation in plumes and the origin of HIMU mantle beneath the Cameroon Line[END_REF][START_REF] Lee | Isotopic variations with distance and time in the volcanic islands of the Cameroon Line; evidence for a mantle plume origin[END_REF] Fig 9

CONCLUSION

Cameroun

Cameroun Line Rb-Sr [START_REF] Rahaman | Age migrations of anorogenic ring complexes in northern Nigeria[END_REF][START_REF] Dickin | A Pb, Sr and Nd isotope study of the basement and Mesozoic ring complexes of the Jos Plateau[END_REF][START_REF] Van Breemen | Age and origin of the Nigerian mesozoic granites: A RbͲSr isotopic study[END_REF] Fig 19.9 ± 1.9 -12.4 ± 2; 6.7 ± 2 -4.2 ± 0.2; 1.95 ± 0.2 -1.5 ± 0.1 K-Ar Rognon et al., 1981;Rognon et al., 1983

FIGURE 1Ͳ1 :

 1Ͳ1 FIGURE 1Ͳ1 : CONCEPTUAL MODEL OF NARROW (A) AND WIDE (B) MARGINS RESULTING FROM DEPTHͲDEPENDENT EXTENSION. ........................................................................................................................................................ FIGURE 1Ͳ2 (A) FORMATION MODEL OF TRANSFORM MARGINS WITH MARGIN STRIKE PARALLEL TO OPENING DIRECTION. (B) MODEL ILLUSTRATING THE DEVELOPMENT OF OBLIQUE MARGINS BY OBLIQUE SHEARING ASSOCIATED TO OBLIQUEͲSLIP FAULTS. ............................................................................................................. FIGURE 1Ͳ3 A SIMPLIFIED MODEL FOR THE EVOLUTION OF TRANSFORM MARGINS. ................................................. FIGURE 1Ͳ4 SCHEMATIC EVOLUTION OF A TRANSFORM MARGIN AND ADJACENT DIVERGENT MARGINS. ............... FIGURE 1Ͳ5 BATHYMETRIC MAP OF THE EQUATORIAL ATLANTIC. .............................................................................. FIGURE 1Ͳ6 MAP SHOWING DIFFERENT MARGIN SEGMENTS OF THE WESTERN SIDE OF THE GULF OF GUINEA. ...... FIGURE 1Ͳ7 BATHYMETRIC FRAMEWORK OF THE IVORY COASTͲGHANA TRANSFORM MARGIN. .............................. FIGURE 1Ͳ8 STRUCTURAL AND SEDIMENTARY CHARACTERISTICS OF THE IVORY COASTͲGHANA MARGINAL RIDGE FIGURE 1Ͳ9 DIFFERENT EXISTING MODELS FOR EXPLAINING THE DEVELOPMENT OF THE MARGINAL RIDGE AND ITS ASSOCIATED VERTICAL DISPLACEMENTS ........................................................................................................... FIGURE 2Ͳ1 CARTE TOPOGRAPHIQUE DU CONTINENT AFRICAIN, DIAGRAMME DE LA DISTRIBUTION DES ALTITUDES DU CONTINENT AFRICAIN ET CARTE MORPHOLOGIQUE ET STRUCTURALE SCHEMATIQUE DE L'AFRIQUE ...... FIGURE 2Ͳ2 VUE OBLIQUE VERS LE NE DE LA TOPOGRAPHIE NW DE L'AFRIQUE. ....................................................... FIGURE 2Ͳ3 CARTE GEOLOGIQUE SIMPLIFIEE DE L'AFRIQUE ....................................................................................... FIGURE 2Ͳ4 CARTE GEOLOGIQUE SIMPLIFIEE DE L'AFRIQUE DE L'OUEST .................................................................... FIGURE 2Ͳ5 ELEMENTS STRUCTURAUX MAJEURS PRECAMBRIENS ET PALEOZOÏQUES DE L'AFRIQUE DE L'OUEST .... FIGURE 2Ͳ6 RECONSTITUTION DE LA BORDURE NW DU CONTINENT DE GONDWANA A LA FIN DU PALEOZOÏQUE. . FIGURE 2Ͳ7 CARTE SIMPLIFIEE DES BASSINS OUEST AFRICAINS BASEE SUR LA CARTE TECTONIQUE DE L'AFRIQUE .. FIGURE 2Ͳ8 LES BASSINS DE RIFT DE LA MARGE DE L'ATLANTIQUE CENTRALE EN POSITION PALEOGEOGRAPHIQUE AU CARNIEN (225 MA) ........................................................................................................................................ FIGURE 2Ͳ9 SCHEMA DE L'EVOLUTION TECTONIQUE ET GEODYNAMIQUE DE L'ATLANTIQUE CENTRAL EN CARTE ET EN COUPES ......................................................................................................................................................... FIGURE 2Ͳ10 LE WESTERN CENTRAL AFRICAIN RIFT SYSTEM AVEC LOCALISATION DU SOUSͲSYSTEME OCCIDENTAL ET CENTRAL ............................................................................................................................................................. FIGURE 2Ͳ11 DYNAMIQUE DU RIFTING CRETACE EN AFRIQUE .................................................................................... FIGURE 2Ͳ12 SCHEMA STRUCTURAL DE LA PARTIE OCCIDENTALE DES WCARS .......................................................... FIGURE 2Ͳ13 EVOLUTION PALEOTECTONIQUE DES BASSINS DE RIFT DE LA PARTIE OCCIDENTALE DU WCARS ......... FIGURE 2Ͳ14 MODELE NEOTECTONIQUE DU CONTINENT AFRICAIN DEPUIS L'EOCENE .............................................. FIGURE 2Ͳ15 LA DISTRIBUTION DU MAGMATISME EN AFRIQUE DE L'OUEST DEPUIS LE DEPUIS DU MESOZOÏQUE ..

FIGURE

  FIGURE 2Ͳ16 LIMITES GENERALES DES ZONATIONS DE L'EXPANSION DE LA CROUTE OCEANIQUE DANS L'OCEAN ATLANTIQUE SUR LES DEUX COTES, SUPERPOSEES SUR UN FOND DES DONNEES GRAVIMETRIQUES DERIVANT DU SATELLITE. ..................................................................................................................................................... FIGURE 2Ͳ17 CHRONOLOGIE SIMPLIFIEE DU TRIAS AU CRETACE DE L'ACCRETION DE LA CROUTE OCEANIQUE, DE L'EVENEMENT MAGMATIQUE, DES FORMATIONS SEDIMENTAIRES PRINCIPALES DE L'ATLANTIQUE CENTRAL ET DES TAUX D'EXPANSION CALCULES POUR DEUX ENDROITS AU MAROC ET NW DE L'AFRIQUE ................... FIGURE 2Ͳ18 OUVERTURE DE L'ATLANTIQUE CENTRAL PROPOSE PAR LABAIL ET AL., 2010 ....................................... FIGURE 2Ͳ19 SCHEMA TECTONOͲSTRUCTURALE DE L'ATLANTIQUE SUD A 84 MA ..................................................... FIGURE 2Ͳ20 RECONSTITUTION DE L'EVOLUTION DE L'OCEAN ATLANTIQUE SUD ET EQUATORIALE PAR MOULIN ET AL., 2010 ............................................................................................................................................................. FIGURE 2Ͳ21 A) RECONSTRUCTION PREͲOUVERTURE DE L'ATLANTIQUE EQUATORIAL A 112 MA ............................. FIGURE 3Ͳ1 (A) MAP SHOWING THE AFRICAN AND SOUTH AMERICAN RIFT SYSTEMS AT ~120 MA DURING DISPERSAL OF GONDWANALAND. ...................................................................................................................... FIGURE 3Ͳ2 SIMPLIFIED GEOLOGICAL MAP OF WEST AFRICA COMPILED FROM CHOUBERT AND FAUREͲMURET (1988), FABRE ET AL. (1996), MILESI ET AL. (2010) AND THIS WORK ................................................................. FIGURE 3Ͳ3 LARGEͲSCALE ONSHORE -OFFSHORE GEOLOGICAL CROSSͲSECTIONS ACROSS NORTHWESTERN AFRICA ............................................................................................................................................................................ FIGURE 3Ͳ4 ESTIMATION OF THE ORIGINAL MINIMUM EXTENT OF SEDIMENTARY DEPOSITS AT THE EDGES OF COASTAL AND INTRACRATONIC BASINS ............................................................................................................. FIGURE 3Ͳ5 GEOLOGICAL CONFIGURATION OF NORTHWESTERN AFRICA AND ADJOINING NORTH AND SOUTH AMERICA DURING LATE TRIASSICͲEARLY JURASSIC (235Ͳ190 MA) .................................................................... FIGURE 3Ͳ6 GEOLOGICAL CONFIGURATION OF NORTHWESTERN AFRICA, ADJOINING SOUTH AMERICA AND THE EASTERN CENTRAL ATLANTIC OCEAN DURING THE VALANGINIAN (140Ͳ133 MA) ............................................ FIGURE 3Ͳ7 GEOLOGICAL CONFIGURATION OF NORTHWESTERN AFRICA, ADJOINING SOUTH AMERICA AND THE EASTERN CENTRAL ATLANTIC OCEAN DURING THE MIDDLE APTIAN (120Ͳ115 MA) ......................................... FIGURE 3Ͳ8 GEOLOGICAL CONFIGURATION OF NORTHWESTERN AFRICA, ADJOINING SOUTH AMERICA AND THE EASTERN CENTRAL ATLANTIC OCEAN DURING THE LATE ALBIAN (107Ͳ100 MA) .............................................. FIGURE 3Ͳ9 GEOLOGICAL CONFIGURATION OF NORTHWESTERN AFRICA, NORTHERN SOUTH AMERICA AND THE EQUATORIAL AND EASTERN CENTRAL ATLANTIC OCEAN DURING THE LATE CENOMANIAN (97Ͳ93 MA) ......... FIGURE 3Ͳ10 GEOLOGICAL CONFIGURATION OF NORTHWESTERN AFRICA, NORTHERN SOUTH AMERICA AND THE EQUATORIAL AND EASTERN CENTRAL ATLANTIC OCEAN DURING THE SANTONIAN (86Ͳ84 MA) ..................... FIGURE 3Ͳ11 GEOLOGICAL CONFIGURATION OF NORTHWESTERN AFRICA AND THE EQUATORIAL AND EASTERN CENTRAL ATLANTIC OCEAN DURING THE MAASTRICHTIAN (72Ͳ66 MA) ........................................................... FIGURE 3Ͳ12 GEOLOGICAL CONFIGURATION OF NORTHWESTERN AFRICA AND THE EQUATORIAL AND EASTERN CENTRAL ATLANTIC OCEAN DURING THE LATE PALEOCENE (61Ͳ56 MA) .........................................................

  passive margins were commonly classified into two categories, (1) rifted and

Figure 1 - 1 :

 11 Figure 1-1 : Conceptual model of narrow (A) and wide (B) margins resulting from depth-dependent extension. (A)Narrow margin can be modelled via rheologically coupled lithospheric crust and mantle, in which the crust breakup occurs while the mantle is still necking. (B) Wide margin can be modelled via rheologically decoupled lithospheric crust and mantle. The breakup of lithospheric mantle precedes that of the crust[START_REF] Huismans | Rifted continental margins; the case for depth-dependent extension[END_REF].

Figure 1

 1 Figure 1-2 (A) Formation model of transform margins with margin strike parallel to opening direction, contrasting

Figure 1

 1 Figure 1-3 A simplified model for the evolution of transform margins. A. Intracontinental stage with active continent to continent contact. B. Syn-transform stage with progressive migration of oceanic spreading ridge along transform margin. C. Post-transform stage with transform faults only active between two oceanic crusts (Mercier de Lépinay, 2016, modified from Mascle and Blarez, 1987).

Figure 1 - 5

 15 Figure 1-5 Bathymetric map of the Equatorial Atlantic. R= rifted (or divergent) margin, T= Transform (or sheared) margin, MAR= Mid-Atlantic Ridge, PFZ= Saint Paul Fracture Zone, RFZ= Romanche Fracture Zone, CFZ= Chain Fracture Zone, AFZ= Ascension Fracture Zone. Location of Ivory Coast-Ghana transform margin is shown in box (after Antobreh et al., 2009).

Figure 1 - 6

 16 Figure 1-6 Map showing different margin segments of the western side of the Gulf of Guinea. MP: Marginal Plateau; TM: Transform Margin; DM: Divergent Margin; CPDM: Cape Palmas Divergent Margin (after Basile, 2015).

  Figure 1-7 and Figure 1-8). The Ivory Coast-Ghana (IC-GH) marginal ridge forms as an elevated and elongated structural high located in the outer corner of the margin, from the Ghanaian shelf to the Southern border of the adjacent Deep Ivorian Basin (Figure 1-7). It is now partly buried under sediments and lines up with the Romanche fracture zone, as well as the continent-ocean transition (Figure 1-7). Marine geophysical cruises, scientific dives and drilling (ODP Leg 159) were carried

Figure 1 - 7

 17 Figure 1-7 Bathymetric framework of the Ivory Coast-Ghana transform margin. Leg 159 sites are indicated by solid circles. Its location is shown in Figure 1-4. The rectangles show the location of the seismic reflection lines shown in Figure 1-78B (Basile et al., 1998).

  ubiquitous erosional unconformity (well dated to be Late Albian in Site 926) tops Unit A. It is interpreted as the post-rift breakup unconformity for the IC-GH transform margin and the adjacent divergent Ivorian margin (Figure 1-8A). Overlying Unit B, is the first post-rift sediments on the divergent segment, but is a 'syn-transform' unit along the IC-GH transform margin. The posttransform units (D-F) showing very little deformation, onlap by a 'post-transform' unconformity the unit B (

Figure 1 - 8

 18 Figure 1-8 Structural and sedimentary characteristics of the Ivory Coast-Ghana marginal ridge. (A) Seismic reflection line across the marginal ridge, the Ivorian Basin and the abyssal plain (Basile et al., 1996). Its location is in Figure 1-67. (B) Seismic velocity model based on a refraction line, see location in Figure 1-7. The Moho is indicated by the bold line[START_REF] Edwards | Synthesis of the crustal structure of the transform continental margin off Ghana, northern Gulf of Guinea[END_REF].

  -9A, Attoh et al. 2004), thick continental sliver transported laterally by transform fault (Figure 1-9B, Le Pichon and Hayes, 1971) and flexural uplift related to erosion discharges of more elevated continental crust (Figure 1-9C,

Figure 1 - 9

 19 Figure1-9 Different existing models for explaining the development of the marginal ridge and its associated vertical displacements[START_REF] Basile | Transform continental margins; Part 1[END_REF].

Figure 2 - 2

 22 Figure 2-2 Vue oblique vers le NE de la topographie NW de l'Afrique[START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF].

  Archéen et Paléoprotérozoïque (4600-1800Ma) à l'Ouest et au Sud de l'Afrique appartiennent aux cratons de l'Afrique de l'Ouest, du Congo et de l'Afrique australe (craton tanzanien, craton du Zimbabwe, craton du Kaapvaal, Figure 2-3, Begg et al., 2009). Les terrains néoprotérozoïques sont représentés par les orogènes (dits « ceintures mobiles ») panafricains formés au cours de l'assemblage ultime des cratons et forment ainsi leurs pourtours (Figure 2-3). Des séries silicoclastiques néoprotérozoïques non déformées sont également présevées dans divers bassins intracratoniques. Des séries Paléozoïques silicoclastiques sont présentes en Afrique septentrionale et dans la dépression du Congo. Il s'agit de grands bassins intracratoniques qui comprennent, notamment des dépôts fluvio-glaciaires et des tillites d'âge Ordovicien-Silurien (Le Heron et al., 2009). Les formations mésozoïques sont présentes principalement dans les bassins de rift continentaux et sur les marges de l'Océan Atlantique (Figure 2-3). Une large surface du continent est couverte par de sédiments continentaux et marins méso-cénozoïques. Les chaînes de l'Atlas se sont formées également à partir de l'Eocène. Les terrains archéens et paléoprotérozoïques d'Afrique de l'Ouest appartiennent au craton Ouest Africain et affleurent dans le Nord du Sahara dans la dorsale Reguibat et au Sud dans la dorsale de Leo-Man (Figure 2-4 and 2-5). Des chaînes néoprotérozoïques et paléozoïques ceinturent le craton. Il s'agit principalement des Mauritanides à l'Ouest et de la chaîne des Dahomeyides et du Hoggar à l'Est. Au centre du craton, s'est formé le grand bassin intracratonique de Taoudeni présentant majoritairement des sédiments néoprotérozoïque-paléozoïques couverts par des formations méso-cénozoïques Figure 2-4 et Figure 2-7). Des rifts crétacés se sont développés essentiellement dans la partie orientale de la zone d'étude. En dehors du bassin sénégalais et du bassin des Iullemmedens (Figure 2-7), les dépôts cénozoïques sont très peu représentés en Afrique de l'Ouest.

Figure 2 - 4

 24 Figure 2-4 Carte géologique simplifiée de l'Afrique de l'Ouest d'après[START_REF] Choubert | International Geological Map of Africa[END_REF][START_REF] Fabre | Evolution des terrains mésocénozoïques d'une marge à l'autre du craton ouest africain, entre le Tanezrouft (Algérie) et l'Adrar de Mauritanie[END_REF][START_REF] Milesi | Tectonic Map of Africa[END_REF] Les sables quaternaires sont enlevés, et les affleurements trais-jurassique au sud-ouest du Hoggar sont incorporés dans le Crétacé Inférieur. Les failles potentiellement réactivées au Méso-Cénozoïque sont présentées.

Figure 2 - 5

 25 Figure 2-5 Eléments structuraux majeurs précambriens et paléozoïques de l'Afrique de l'Ouest. (1) limite du craton Ouest Africain, (2) Faille, (3) Chevauchement, (4) Socle Archéen Supérieur, (5) Socle Protérozoïque Inférieur, (6) Orogenèse Panafricaine, (7) Orogenèse Paléozoïque Supérieur, (8) Couverture Protérozoïque Supérieur-Paléozoïque Supérieur plissée, (9) Couverture Protérozoïque Supérieur-Paléozoïque Supérieur, (10) Couverture Post-Paléozoïque.

  terrains sédimentaires paléozoïques se retrouvent tout autour du Hoggar et sont préservés dans les bassins des Iullemedens, de Murzuk et du Sahara septentrional/Sud Algérien (Figure 2-7). Ces terrains ont été cintrés et exhumés au cours du bombement du Hoggar au

  Volta à l'Est de la dorsale de Léo-Man est considéré comme étant un bassin d'avant-pays de la chaîne des Dahomeyides (Figure 2-5 à Figure 2-7,[START_REF] Deynoux | Pan-African tectonic evolution and glacial events registered in Neoproterozoic to Cambrian cratonic and foreland basins of West Africa[END_REF][START_REF] Roussel | Geophysics and the Crustal Structure of West Africa[END_REF]. Le bassin de Kandi, situé au Sud du bassin des Iullemedens, est découpé par divers accidents panafricains orientés N15-20°E dont la faille principale de Kandi sur la bordure ouest du bassin est réactivée à la fin du Crétacé (Figure2-7, Guiraud et Alidou, 1981). Un autre bassin Paléozoïque, le bassin Bové (Cambro-Dévonien Supérieur), est localisé sur la connexion entre la chaîne des Rokelides et la chaîne des Bassarides (Figure 2-5 à Figure 2-7).

Figure 2 - 8

 28 Figure 2-8 Les bassins de rift de la marge de l'Atlantique Centrale (CAM) en position paléogéographique au Carnien (225 Ma). (A) bassins de CAM: a, bassin d'Argana; c, bassin de Culpeper; cb, bassin de Carson; cc, region de Clubhouse Crossroads dans le bassin de South Georgia; d, bassins de Dan River-Danville; df, bassin de Deerfield; dr, bassin de Deep River; e, bassin de Essaouira; em, bassins les plus à l'est avec la formation d'Eagle Mills; f, bassin de Fundy; fm, Farmville et des bassins associés; g, bassin de Gettysburg; gb, bassin de Georges Bank; h, bassin de Hartford; j, bassin de Jeanne d'Arc; m, bassin de Mohican; n, bassin de Newark; na, bassin de Nantucket; no, bassin de Norfolk; o, bassin d'Orpheus; p, bassin de Pomperaug; t, bassin de Taylorsville. (B) Reconstruction de la Pangée au Carnien (225 Ma), montrant la zone de rifting (gris) et les bassins de CAM[START_REF] Olsen | Stratigraphic record of the early Mesozoic breakup of Pangea in the Laurasia-Gondwana rift system[END_REF].

  Le rifting a commencé au Trias Supérieur avec une direction d'extension NW-SE en formant des grabens/demi-grabens (Figure 2-9A). Des chevauchements d'âge Paléozoique de direction NE-SW ont été réactivés en failles normales en Amérique du Nord. Ceux qui sont orientés E-NE ou NNE ont rejoué en failles normales avec une composante décrochante sénestre ou dextre. x L'inversion avec une direction de compression NW-SE a eu lieu durant la transition riftdrift ou au début de l'expansion océanique au Tiras Supérieur-Crétacé Inférieur (Figure 2-9B et C). Des failles inverses de direction NE-SW se forment, en partie par la réactivation des failles normales. L'origine de cette inversion est expliquée par la force de poussée à la ride liée à la remontée asthénosphère et à la résistance initiale du continent contre le déplacement (Figure 2-9B et C).

Figure 2 - 9

 29 Figure 2-9 Schéma de l'évolution tectonique et géodynamique de l'Atlantique Central en carte et en coupes. (A) Trias Moyen et Supérieur, (B) Trias Supérieur et Jurassique Inférieur, plus ou moins pendant la CAMP qui met en place des dykes. Le rifting se termine au Sud et l'inversion a lieu en formant des failles inverses et des plis. (C) Jurassique Inférieur-Crétacé Inférieur, après la CAMP. L'expansion de la croûte océanique commence au Sud et en Afrique de l'Ouest. Le rifting au Nord se termine avant la fin du Jurassique Inférieur-début du Jurassique Moyen. L'inversion se met en place au Nord avant ou pendant le Crétacé Inférieur[START_REF] Withjack | Diachronous Rifting, Drifting, and Inversion on the Passive Margin of Central Eastern North America: An Analog for Other Passive Margins[END_REF].

  Figure 2-9B). L'Atlantique Equatorial s'ouvrait à cette époque par une zone de cisaillement dextre dans les bassins de rift offshore et un cisaillement sénestre dans le fossé de la Bénoué (Figure 2-7 et Figure 2-12).

CHAPTER 2 :

 2 Figure 2-10 Le Western Central Africain Rift System (WCRS) avec localisation du sous-système occidental (WAS) et central (CAS). Lignes continues : failles majeures, lignes tiretées : failles supposées, lignes pointillées : Axe du futur rift Est-Africain. Le rectangle rouge délimite les bassins d'interêt pour l'Afrique de l'Ouest(Genik, 1993).

Figure 2 -

 2 Figure 2-11 Dynamique du rifting crétacé en Afrique (modèle de Guiraud et al. (2005)). (A) Barrémien Supérieur (122 Ma). (B) Albien Inférieur (110 Ma). A.B.= bloc austral, A.N.B.= bloc Arabo-Nubien, W.B.= bloc Ouest, Ap= plaque apulienne. 1 : Croûte océanique, 2 : Faille ou décrochement, 3 : Décrochement majeur ou faille de transfert. 4 : Mouvement relatif du bloc Arabo-Nubien au Crétacé Inférieur, 5 : Chevauchement.

Figure 2 -

 2 Figure 2-14 Modèle néotectonique du continent africain depuis l'Eocène, selon Guiraud et al. (2005). (1) région cratonique, (2) décrochement, (3) failles, (4) rift, (5) chaîne Alpine, (6) zone soulevée, (7) zone soulevée avec magmatisme, (8) volcans. Che : Cheliff, Da : Darfur, DD : Dj.Druze, Gn : Garian High, Gu : Guinea, H : Hoggar, Hj : Haruj, Hod : Hodna, JP : Jos Plateau, Rb : Rharb, Rg :Rungwe, Ti : Tibesti.

CHAPTER 2 :

 2 Figure 2-15 La distribution du magmatisme en Afrique de l'Ouest depuis le depuis du Mésozoïque[START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF].

Figure 2 -

 2 Figure 2-16 Limites générales des zonations de l'expansion de la croûte océanique dans l'Océan Atlantique sur les deux côtés, superposées sur un fond des données gravimétriques dérivant du satellite (free-air, one arc-minute grid of uniform coverage). Les anomalies magnétiques sont indiquées en rouge : ECMA : Côte Est de l'Amérique du Nord, WACMA : Côte de l'Afrique de l'Ouest, BSMA : Blake Spur, ABSMW : Blake Spur Africain. ECMA est présenté en deux couleurs (rouge et orange) selon son amplitude. Les zones de fracture océaniques et les structures tectoniques majeurs sont indiquées. Les provinces de l'anomalie magnétique entre ECMA/WACMA et Chron M25, et entre Chron M25 et M0, constituent Jurassic Magnetic Quiet Zone (JMQZ). MAR, Mid-Atlantic Ridge; GB, Grand Banks of

Figure 2 -

 2 Figure 2-17 Chronologie simplifiée du Trias au Crétacé de l'accrétion de la croûte océanique, de l'événement magmatique, des formations sédimentaires principales de l'Atlantique Central et des taux d'expansion calculés pour deux endroits au Maroc et NW de l'Afrique(Labail et al.,2010). M0 a été redaté plus récemment à 120.6 Ma[START_REF] Gaina | The African Plate: A history of oceanic crust accretion and subduction since the Jurassic[END_REF].

CHAPTER 2 :

 2 Figure 2-18 Ouverture de l'Atlantique Central proposé par Labail et al., 2010. L'Amérique du Nord est fixée. M0 est daté plus récemment 120.6 Ma (Gaina et al., 2013).

Figure 2 -

 2 Figure 2-19 Schéma tectono-structurale de l'Atlantique Sud à 84 Ma. A.R. : Ride d'Abimael (ancienne ride avortée) FZ, Zone de Fracture (Moulin et al., 2010).

Figure 2 -

 2 Figure 2-20 Reconstitution de l'évolution de l'océan Atlantique Sud et Equatoriale par Moulin et al., 2010. Le bloc Ouest Africain est fixé. La localisation de la déformation intraplaque entre deux chrons est marquée par des lignes

  Figure 2-21 a) Reconstruction pré-ouverture de l'Atlantique Equatorial à 112 Ma. Les données gravimétriques sont montrées dans la partie océanique. L'Afrique est fixée. L'Amérique du Sud et les grilles gravimétriques sont tournées suivant les petits cercles. b) Reconstruction de l'Atlantique Equatorial à Mid-Albien (vers 107.5 Ma ) (Moulin et Labail, Communication personnelle) c) Reconstruction à 84 Ma (C34) (Moulin et al., 2010).

Figure 3 -

 3 Figure 3-1 and Figure 3-2). Those margins belonged to a large-scale network of rifts that led to the final dispersion of the Gondwana supercontinent by break-up between South America and Africa during the Early Cretaceous (Figure 3-2A). Counterclockwise rotation of the African plate produced a northward rift propagation leading to the formation of the South Atlantic Ocean under dominantly normal divergence, whereas the future Equatorial Atlantic domain underwent dextral-

Figure 3

 3 Figure 3-1 (A) Map showing the African and South American rift systems at ~120 Ma during dispersal of Gondwanaland (modified after Frizon de Lamotte et al., 2015). (B) Structural map of northwestern Africa showing Meso-Cenozoic faults and sedimentary basins (after Kogbe, 1981 and Milesi et al., 2010). Geological contours are simplified from Figure 3-2. The names of the main Early Cretaceous intracontinental rifts are indicated (bold font). The frame of Figure 3-1B is shown in red on Figure 3-1A.

(

  Figure 3-1). Our work is based on a series of large-scale offshore -onshore geological crosssections and nine maps showing successive geological configurations since 200 Ma, taking into account (1) restoration of the position of Northern South America relative to Northwestern Africa,

  e., the West African craton), fringed by Panafrican (Late Neoproterozoic) and Variscan mobile belts (Figure 3-1 and Figure 3-2). Panafrican crystalline rocks of the Saharan craton, outcropping as the Nigerian and Hoggar shields and the Tibesti massif, form the basement of the sedimentary basins located East of the West African craton (Figure 3-1). Meso-Cenozoic sediments are preserved in several intracratonic basins around the Hoggar shield. The Taoudeni, South Algerian, Murzuc, Chad and Iullemmeden basins developed either on Neoproterozoic-Paleozoic platform sequences

Figure 3 - 2

 32 Figure 3-2 Simplified geological map of West Africa compiled from Choubert and Faure-Muret (1988), Fabre et al. (1996), Milesi et al. (2010) and this work. Quaternary sand cover has been omitted, and small Triassic-Jurassic sedimentary outcrops in the Tim Mersoi basin were included in Lower Cretaceous sediment map units. Lower Cretaceous and Paleogene continental sediments are grouped as the "Continental Intercalaire" and "Continental

Figure 3 - 3

 33 Figure 3-3 Large-scale onshoreoffshore geological crosssections across northwestern Africa based on various sources, among which Helm (2009) for the offshore sections, Choubert and Faure-Muret (1988) and Milesi et al., (2010) for the intracontinental domains. See section locations on the inset map. Syn-rift fault on passive margins are omitted for clarity.

  potential minimum areal extent of sedimentary basins by estimating the map width of the subsequent erosion they have undergone at their margins. Let us consider ǻZ as the denudation due to a drop in base level consecutive to an uplift and/or a sea level change from time T1 to T2. E is the resulting inward (i.e., towards the basins' main depocenter) retreat of basins' edges and S the topographic slope of a basin's margin (Figure3-4B). Ei and Si and Es and Ss are defined for the inlandward slope of intracratonic basins and the seaward slope of coastal basins, respectively (Figure3-4B). Assuming a negligible short-wavelength relief, which is reasonable for cratonic surfaces and their marginal upwarps, we have E = ǻZ/S.

  Figure 3-4 Estimation of the original minimum extent of sedimentary deposits at the edges of coastal and intracratonic basins. (A) Schematic illustration of the retreat (E) of an intracratonic basin edges between time T1 to T2 (modified after Sloss and Scherer, 1975). (B) Cross-section of a marginal upwarp showing the influence of topographic slopes (S) on the original horizontal extent of sedimentary deposits and their erosion at basin edges. (C) Curves showing the relationships among the regional slope (S), the original extent of sediments (E) and denudation (ǻZ). See text for further explanations.

  reflect burial under sediments, whereas cooling periods indicate dominant erosion-driven exhumation and therefore an eroding landsurface above. Published temperature-time paths obtained by data inversion have been used (Appendix 2, Figure3-2). For the time step corresponding to each paleo-map, heating or cooling sample locations are reported and used to semi-quantitatively enlarge or restrain the potential original extent of sedimentation areas, respectively. Samples undergoing rapid cooling/heating (cooling/heating rate higher than 1°C/Ma) were distinguished from those undergoing slow cooling/heating. Samples with similar thermal histories in the same region were gathered and displayed under a single symbol. All the constraints used above allow mapping the original minimum extent of sedimentation areas (in lighter colors than those of the preserved deposits; Figure3-5 to Figure3-13). Conversely, continental areas mapped as exposed to erosion or sediment by-passing therefore correspond to their maximum potential extent.

  Figure 3-13).

  Figure 3-5 to Figure 3-13).

  [START_REF] Heine | Kinematics of the South Atlantic rift: Solid Earth[END_REF] are based on a reconstruction of the stretching and subsidence due to rifting from the Berriasian (145 Ma) to the Late Albian (104 Ma) before continental breakup.[START_REF] Moulin | A new starting point for the South and Equatorial Atlantic Ocean[END_REF] suggest another pre-opening fit at 112 Ma, based mainly on correlations of structures across the Equatorial Atlantic domain (magnetic lineaments, conjugate plateaus, fracture zones), without considering syn-rift fault patterns and deformation. The pre-opening fit ofHeine et al.,

  100 Ma, Figure 3-8), Late Cenomanian (97-93 Ma, Figure 3-9), Santonian (86-84 Ma, Figure 3-10), Maastrichtian (72-66 Ma, Figure 3-11), Late Paleocene (61-56 Ma, Figure 3-12) and Oligocene (34-23 Ma, Figure 3-13). For specific localities, structures or sedimentary basins' locations, the reader may refer to Figure 3-1 and Figure 3-2.

  This suggests a complex migration of depocenters through time potentially driven by the interference of vertical movement of basement highs and marginal upwarps at contrasted wavelengths. The width of the present-day erosional marginal upwarp is consistent along the CHAPTER 3 :PALEOGEOGRAPHIC AND STRUCTURAL RECONSTRUCTION 84 Central Atlantic margin (ca. 800 km; Figure 3-3A and B). It varies greatly along the Equatorial margins, from ca. 800 km in Ivory Coast-Ghana to less than 400 km in Benin-Togo (Figure 3-3C and D). Meso-Cenozoic series are thinner in the intracratonic basins (less than 2 km thick) than in the marginal basins (up to 5 km thick). Triassic and Jurassic sediments are mainly preserved along the Central Atlantic margin (Figure 3-3A and B) due to Latest Triassic rifting. Lower Cretaceous post-rift deposits are much thicker along the Central Atlantic margin than the Equatorial margins (Figure 3-3C and D). Cenozoic sediments are thinner but emplaced over larger widths on the Central Atlantic margin, suggesting comparable volumes on both types of margins (Figure 3-4A and B). Cenozoic sediments are well preserved along the Equatorial Atlantic margins (up to 3 km thick), especially along the Ghana-Benin margin that has been partly fed by the Niger Delta located to the East (e.g., Figure 3-1B). Triassic-Earlier Jurassic (235-190 Ma): The CAMP and the Opening of the Central Atlantic Ocean (Figure 3-5)

Figure 3 - 5

 35 Figure 3-5 Geological configuration of Northwestern Africa and adjoining North and South America during Late Triassic-Early Jurassic (235-190 Ma). Magmatic features of the Central Atlantic Magmatic Province (CAMP) come from Jourdan et al. (2009). The range in age of the magmatic clusters is indicated. The present-day shorelines of North America and Northern South America (thin blue lines) are restored to their position relative to fixed Africa at the end of the considered time interval. Magmatic occurrences emplaced during the considered time interval for the map, unless if specified otherwise on the map or in the explanation. Open circles are the localities from Figure 3-1B and Figure 3-2.

Figure 3 - 6

 36 Figure 3-6 Geological configuration of Northwestern Africa, adjoining South America and the Eastern Central Atlantic Ocean during the Valanginian (140-133 Ma). Same conventions as in Figure 3-5.

  Figure 3-7 Geological configuration of Northwestern Africa, adjoining South America and the Eastern Central Atlantic Ocean during the Middle Aptian (120-115 Ma). Same conventions as in Figure 3-5.

  Figure 3-8 Geological configuration of Northwestern Africa, adjoining South America and the Eastern Central Atlantic Ocean during the Late Albian (107-100 Ma). Same conventions as in Figure 3-5.

Figure 3 - 9

 39 Figure 3-9 Geological configuration of Northwestern Africa, Northern South America and the Equatorial and Eastern Central Atlantic Ocean during the Late Cenomanian (97-93 Ma). Same conventions as in Figure 3-5

  Equatorial Atlantic margins' basins record more than 200 meters of relative sea level fall, suggesting uplift in those basins. The Santonian sedimentary hiatus along the Sierra Leone-Liberia margin also indicates uplift and erosion at that time. Furthermore, vitrinite reflectance data from certain boreholes along the Equatorial Atlantic margin suggest at least 400-500 m of erosion during the Late Cretaceous, which may result from this Santonian event.Transform-controlled anticlines continue to grow along the Ghana-Benin margin. Reactivation of the Romanche transform fault leads to more than 1 km of erosion on the IC-GH marginal ridge (Figure3-1 and Figure3-9) during the Late Cretaceous according to vitrinite reflectance data. In Northwestern Africa, the area exposed to erosion has grown significantly, suggesting very-long wavelength uplift that could tentatively be linked to the inversion event. The eroding domain seems to form a very wide continuous marginal upwarp between the Benue Trough and the Reguibat shield.

Figure 3 -

 3 Figure 3-10 Geological configuration of Northwestern Africa, Northern South America and the Equatorial and Eastern Central Atlantic Ocean during the Santonian (86-84 Ma). Same conventions as in Figure 3-5.

  Figure 3-11 Geological configuration of Northwestern Africa and the Equatorial and Eastern Central Atlantic Ocean during the Maastrichtian (72-66 Ma). Same conventions as in Figure 3-5.

Figure 3 -

 3 Figure 3-12 Geological configuration of Northwestern Africa and the Equatorial and Eastern Central Atlantic Ocean during the Late Paleocene (61-56 Ma). Same conventions as in Figure 3-5.

  Figure 3-13 Geological configuration of Northwestern Africa and the Equatorial and Eastern Central Atlantic Ocean during the Oligocene (34-23 Ma). Same conventions as in Figure 3-5.

  -14). To the North, Microplate 2 represents the continental lithosphere of Central Atlantic affinity remaining stable during Cretaceous rifting. Microplate 3 accommodates the NE-extension between Microplate 1 and the Nubian plate (4) drifting northeastward (Figure 3-14). Microplate 5 occupies an intermediate position between Microplate 1, 3, 4, 6 (Central and Southern Africa block) and 7, and has therefore a complex behavior given the various kinematic incompatibilities it has to absorb along its various boundaries. Nevertheless, microtectonic data along its northern and southern boundary faults could suggest escape tectonic of that block towards the ENE, in the direction of divergence of Nubia (4). The shape and kinematic boundary conditions of microplate 1 requires internal deformation (shearing) and rotation during rifting, in particular to accommodate (i) the distributed, en-échelon transtensional kinematics of the Equatorial margin, (ii) extension along its boundaries with microplate 3, and (iii) transfer faulting at the boundaries with microplate 2 (Figure 3-14). Internal deformation in the vicinity of the Equatorial margin requires reactivation of the basement faults inside microplate 1, which acted as terminations of the transforms into the continent.

Figure 3 -

 3 Figure 3-14 Microplate model for northwestern Africa and adjoining northern South America during Aptian rifting (based on the reconstruction shown in Figure 3-7). Six microplates are distinguished in intracontinental Africa. Open circles are the localities from Figure 3-1 and Figure 3-2B.

Figure 3 -

 3 Figure 3-15 Successive configurations of the Equatorial Atlantic Ocean during the Early Cretaceous. G-L: Guinea-Liberia margin; IC: Ivory Coast margin; GH-B: Ghana-Benin margin. (A) Barremian: the Guinea-Liberia margin was undergoing rifting, whereas rifting only initiated along the Ivory Coast and Ghana-Benin margins. (B) Main Aptian rifting stage: all the Equatorial Atlantic margins underwent interference between dextral strike-slip (along incipient transforms) and normal faulting. Oceanic spreading was active between the South Atlantic Ocean and the eastern half of the Ghana-Benin margin. Spreading also initiated along the Ivory Coast-Ghana and Guinea-Liberia margins, forming two isolated domains of oceanic crust. (C) Late Albian break-up stage. A WNW trending rift branch formed

Figure 3 -

 3 Figure 3-16 Synthetic paleogeographic map of northwestern Africa showing the evolving positions of shorelines (solid lines) or minimum extent of non-marine sedimentary deposits (dashed lines) through the Meso-Cenozoic (synthetized from Figure 3-5 to Figure 3-13). Depositional areas are filed with levels of grey color. Darker zones represent longerlived depositional / sediment preservation area. Four segment types are distinguished along the marginal upwarp.

  of long-wavelength lithospheric deformation and coeval erosion, the current West African intracratonic basins are only residual fragments of a large Saharan basin that once covered up to two thirds of the pre-Mesozoic continental substrate of Northwestern Africa.Therefore, those basins should not be studied as separate entities as it has been done since early geological exploration of Northwestern Africa. Likewise, the present compilation of paleogeography, paleocurrent, and thermochronological data shows that the Hoggar shield, which was considered as a large massif since the Early Mesozoic by most authors, only emerged since the Late Eocene. It is the result of the bursting, distortion and erosion of the Saharan basin by the Hoggar hot-spot swell.

  construction of Meso-Cenozoic paleo-geological / palinspastic maps allows reassessing the opening mode of the Equatorial Atlantic Ocean and constraining the structural, sedimentary and erosional history of its African continental margins. The maps further allow linking the evolution of the continental margins to that of their far African hinterland, with implications for the understanding of the coupling between long-wavelength deformation and sediment transfer processes over paired shield area-continental margin systems.Oblique rifting of the Equatorial Atlantic domain started in the Valanginian (140-133 Ma), following plate reorganization and abandonment of a rift system that was propagating from the Central Atlantic Ocean across northern South America. Rifting of the Equatorial Atlantic propagated eastward from the Guinea margin until the Aptian (ca. 113 Ma). The rift system consisted in en-échelon dextral strike-slip faults (future tranforms) alternating with normal fault and was connected with an inland rift network under an overall regime of NE-SW extension in present coordinates. The whole rift-transform system almost split the Northwestern African continental domain into 6 microplates and a new syn-rift kinematic model is proposed that allows refining the pre-opening fit of Africa and North America. Final continental breakup occurred at the Ivory Coast-Ghana marginal ridge during the Late Albian.

  This study was funded by Total Exploration and Production through the Transform Sourceto-Sink Project (TS2P). We acknowledge Total for providing data and for allowing publication of the study. Total R&D research group is thanked for discussions as well as scientific and technical support. We are grateful to Maryline Moulin and Daniel Aslanian for kindly providing us with their kinematic model of the Equatorial Atlantic Ocean. le résultat d'une flexure plus importante des parties proximales des segments transformants au début du post-rift, qui empêche la préservation. Nous avons également pu documenter, dans la partie proximale des segments divergents, un soulèvement régional (x 100 m) durant le Santonien (ca. 84 Ma) qui pourrait être lié à la dynamique mantellique ou à une réorganisation intraplaque des contraintes.

  lithosphere stretching, alternating segments where the stretching is fully controlled by the transform fault and segments where the stretching is more oblique or simply divergent (e.g.[START_REF] Basile | Transform continental margins; Part 1[END_REF][START_REF] Basile | The initiation of pull-apart basins and transform continental margins: results from numerical experiments of kinematic partitioning in divergent settings[END_REF] Mercier de Lépinay et al., 2016). Mercier deLépinay et al. (2016) defined a typology of segment based on present-day geometries of the margin, however, the impact of this complex 3D stretching distribution on the post-rift evolution of the margin in general and the stratigraphic architecture in particular, has not been addressed. This spatial variability of lithosphere stretching is nonetheless expected to have very different impacts on vertical motions of the margin, especially in the necking domain, as it acts on the thermal and gravity driven isostasy, CHAPTER 4 :STRUCTURE AND MESOZOIC STRATIGRAPHY OF THE EQUATORIAL ATLANTIC MARGIN 115 as well as on the subsidence/uplift patterns related to the flexural isostasy response of the lithosphere to both stretching and (un)loading effects of surface processes. The aim of this study is to establish the impact of the spatial variations of lithosphere stretching during the rifting on the post-rift stratigraphic architecture by analyzing the difference in behavior of different segments of the same margin during the post-rift. To do this, we used seismic and well data to study the tectonic and stratigraphic history of each segment at the scale of the whole African Equatorial Atlantic margin, and compared them. We analyzed the immediate post-rift stratigraphic architecture in the light of the geometry of crustal thinning pattern and obliquity with respect to the direction of the transforms, and discussed the post-rift vertical displacements associated with different margin segment types.

Figure 4

 4 Figure 4-1 (a) Simplified geological map (modified from Choubert and Faure-Muret, 1988) and (b) the location of the study area. Topographic map is from www.noaa.gov.

  propagradation/regression (seaward migration), aggradation (vertical migration) and retrogradation/transgression (landward migration). Key stratigraphic surfaces are distinguished when combining the shoreline trajectory and truncations associated to the surface (onlap, toplap, downlap and erosional truncation, Figure 4-3b). An subaerial unconformity (UN) is defined when the shoreline migrates seaward and/or downward during an acceleration of propagation (Figure 4-3b). It can be correlated seaward to a marine conformity or the bottom of basin-floor masstransport deposits. A maximum flooding surface (MFS) is defined when a retrogradation evolves CHAPTER 4 :STRUCTURE AND MESOZOIC STRATIGRAPHY OF THE EQUATORIAL ATLANTIC MARGIN 119 into a propagradation. Flooding surfaces (FS), also called as maximum regressive surfaces (MRS)

Figure 4 - 3

 43 Figure 4-3 Seismic stratigraphy method used in this study (after Jermannaud et al., 2010). Definition of the (a) offlap break, (b) the offlap break migration and associated stratigraphic surfaces and (c) the systems tracts and depositional

  structures of Ivory Coast margin vary from the West to the East. The western transform segment is controlled by the Saint Paul transform fault, whereas the eastern one is a NW-SE trending divergent segment (Figure 4-2 and Figure 4-4). During the Lower Cretaceous, the Western transform segment underwent mainly strike-slip syn-rift faulting and is associated with a relatively narrow necking width (ca. 40 km; Figure 4-4a). Continent-ocean transition (COT) is almost clear-cut with an oceanic crust clearly identified and marked by the strong reflector of the Moho. Anticlines formed locally by reactivation of syn-rift faults during the Upper Cretaceous.

  . Whatever the exact nature of that COT domain, the necking zone is wider than along the divergent transform segment (> 80 km).

Figure 4 - 4 Figure 4 - 5

 4445 Figure 4-4 Structural and stratigraphic interpretation of cross-sections in the Ivory Coast Basin cross-sections. See location in Figure 4-2 and text for details.

Figure 4 - 6

 46 Figure 4-6 Structural and stratigraphic interpretation of regional cross-sections along the Ghana margin segment. See location in Figure 4-2.

Figure 4 - 7

 47 Figure 4-7 Structural and stratigraphic interpretation of regional cross-sections along the Togo-Benin margin segment. See location in Figure 4-2.

  segments (Figure 4-1). Syn-rift structures vary along (from NW to SE) and across the margin (from proximal to distal domains; Figure 4-8). To the northwest of the Sierra Leone segment, syn-rift deformation is associated with strike-slip faulting (Figure 4-8a), whereas, to the southeast, it formed more classic tilted blocks (Figure 4-8b). To the northwest, a distal crustal domain, thinner than the oceanic crust has been identified and interpreted as a hyperextended continental crust. That domain is associated with a slight Moho upwarp and buried under a thick sedimentary unit showing normal faults and strike-slip flower structures (Figure 4-2 and Figure 4-8a). The width of the necking zone along that segment is about 80 km (Figure 4-8a and b).

  Figure4-9 Synthetic chart summarizing the deformation regimes and the regional depositional environments along the Equatorial Atlantic margin, as well as major deformation or sedimentary events of the African plate. Tectonic and stratigraphic evolution of each margin segment is presented by a synthetic lithologic log of the shelf and cartonillustrated depositional patterns.

Figure 4

 4 Figure 4-9). The proximal parts of the early post-rift sedimentary wedges are preserved only on the shelf of divergent segments. Along transform segments, they are represented by an erosion surface on the shelf and the distal parts of the wedge are preserved only on the slope and abyssal plain (Figure 4-9).

  margin experienced contrasting histories of post-rift vertical displacements depending on their maegin type and obliquity (transform or divergent segments; Figure4-11).During the early post-rift (Upper Cretaceous), the divergent segment (Eastern Ivory Coast) experienced mostly thermal subsidence (except for a transient potential uplift event recorded on the platform during the Santonian; Figure4-5 and Figure4-9). For transform margin segments (Western Ivory Coast and Ghana segments), the Upper Cretaceous is recorded by a hiatus on the shelf suggesting sediment by-pass across the platform and/or erosion. There are two possible scenarios in terms of vertical displacements on the shelf of transform margin segments during the early post-rift in that case: (1) Either Upper Cretaceous sediments were deposited and eroded later on (along with some of underlying syn-rift deposits) in response to an accommodation reduction driven by an uplift event, or, (2) sediments by-passed the shelf throughout the Upper Cretaceous (also eroding away some syn-rift deposits) in absence of accommodation creation related to a steady uplift compensating thermal subsidence. In the first case, the uplift event could correspond to the Santonian event documented on the divergent segment (Eastern Ivory Coast). In the second case, the more steady uplift on the shelf throughout the Upper Cretaceous could be related to a progressive tilting of the margin and/or to the flexure response of the stretched lithosphere. Unpublished vitrinite reflectance data from wells located on the shelf indicate maximum burial temperatures compatible with over 500 km of erosion during the Upper Cretaceous (M. Dall'Asta, personal communication). These data are compatible with

CHAPTER 4 :

 4 Figure 4-11 Schematic evolution of the different vertical displacement histories along divergent and transform margin segments. See text for details.

(

  iv) Transform and divergent segments accordingly underwent different histories of early post-rift vertical displacements. The divergent segment (Eastern Ivory Coast) experienced mostly thermal subsidence, allowing for the preservation of the proximal Upper Cretaceous wedge. It was nonetheless impacted by some transient uplift of the platform domain during the Santonian (84 Ma). Transform segments, with narrower necking zones than divergent segments, underwent larger flexural uplift in their proximal parts that would account for the lack of preservation of the early CHAPTER 4 :STRUCTURE AND MESOZOIC STRATIGRAPHY OF THE EQUATORIAL ATLANTIC MARGIN 137 post-rift wedge of most proximal terms. However, the Santonian post-rift rejuvenation event observed along several Atlantic margins, related to either mantle driven dynamics or regional changes in lateral stress regime, may superimpose along transform segments.

(

  ~100.5 Ma), Top Cenomanian (~94 Ma), Top Santonian (~84 Ma) and Top Maastrichtian (~66 Ma) (Figure 5-2). In the Sierra Leone-Liberia Ivory Coast basins, we used a fifth Top Campanian (~72 Ma) horizon. In Ivory Coast and Ghana-Benin basins, we also used six Cenozoic horizons that were interpreted by D. Huyghe: Top Paleocene (~56Ma), Top Eocene (~34Ma), Oligocene unconformity (~ 31 Ma), and three Miocene horizons (Figure 5-2; Huyghe, 2016).

Figure 5 - 1

 51 Figure 5-1 Simplified onshore geologic map and oceanic curst ages of study zone (modified from Choubert and Faure-[START_REF] Choubert | International Geological Map of Africa[END_REF]. Location of non-extrapolated and extrapolated cross-section are indicated, as well as used seismic profiles from[START_REF] Emery | Continental margin off western Africa; Angola to Sierra Leone[END_REF]. SL: Sierra Leone, LB: Liberia, IC: Ivory Coast, GH: Ghana, TG: Togo, BN: Benin.

CHAPTER 5 :Figure 5 - 2

 552 Figure 5-2 Used regional horizons from seismic and well data interpretation in Sierra Leone-Liberia (SL-LB), Ivory Coast (IC) and Ghana-Benin (GH-BN) basins and their stratigraphic ages and associated uncertainties. Major erosional unconformities are in red lines, which present higher age uncertainties (modified from Loparev, 2016).

  Figure 5-4 Extrapolated cross-sections along the Ivory Coast margin from West to East (IC1 to IC7). Location is indicated in Figure 5-1.

Figure 5 -

 5 Figure 5-5 Non-extrapolated cross-sections along the Ghana-Benin margin from West to East (GH-BN1 to GH-BN7). Locations are indicated in Figure 5-1.

  Figure 5-6 Method used for sedimentary volume and accumulation rate estimation. The volume of sediment V¨t in the basin during the time interval ¨t is estimated by an interpolation between cross-sections. Cross-sections are selected to represent the variability of stratigraphic architecture of the basin and cover the whole sedimentary wedge from onshore to the distal oceanic basin. (After[START_REF] Guillocheau | Quantification and causes of the terrigeneous sediment budget at the scale of a continental margin; a new method applied to the Namibia-South Africa margin[END_REF]

  in situ sediment productions (i.e. carbonates). To do this we compiled the carbonate contents of 9 wells in Ghana-Benin proximal basin (mostly on the shelf), 9 wells in Ivory Coast proximal basin CHAPTER 5 :ESTIMATION OF ACCUMULATED SEDIMENTARY VOLUMES ON THE AFRICAN EQUATORIAL ATLANTIC MARGIN 147 and 5 wells in Sierra Leone-Liberia proximal basin (Figure 5-7a, b and c). We estimated the mean percentage of carbonates and its variability for each time interval in each basin (Figure 5-7d).

CHAPTER 5 :

 5 Figure 5-7 (a) 9 compiled wells with CaCo3 percent in Ghana-Benin; (b) 9 compiled wells with CaCo3 percent in Ivory Coast; (c) 5 compiled wells with CaCo3 percent in Sierra Leone-Liberia; (d) Estimation of mean carbonate percent for the Ghana-Benin, Ivory Coast and Sierra Leone-Liberia basins with uncertainties.

Figure 5 - 8

 58 Figure 5-8 Used negative exponential law of porosity depending on the depth. Porosity range of sand and clay are from Dauteuil et al. (Submitted).

CHAPTER 5 :

 5 ESTIMATION OF ACCUMULATED SEDIMENTARY VOLUMES ON THE AFRICAN EQUATORIAL ATLANTIC MARGIN 149

  accumulation rates of the three basins, based on nonextrapolated cross-sections are shown in Figure 5-9A and on extrapolated cross-sections in Figure 9B. For Cenozoic, the number of time increments varies from one in Sierra Leone-Liberia to six in Ivory Coast and five in Ghana-Benin. For the Upper Cretaceous the number of time increments is more homogeneous: four increments in Sierra Leone-Liberia and Ivory Coast basins, and three in Ghana-Benin basin as the Campanian and Maastrichtian intervals were grouped.

CHAPTER 5 :

 5 Figure 5-9 (A) Accumulated volumes and rates and their uncertainties, based on non-extrapolated cross-sections in Sierra Leone, Ivory Coast and Ghana-Benin; (B) Accumulated volumes and rates and their uncertainties estimated based on extrapolated cross-sections in Sierra Leone and Ivory Coast.

CHAPTER 5 :

 5 ESTIMATION OF ACCUMULATED SEDIMENTARY VOLUMES ON THE AFRICAN EQUATORIAL ATLANTIC MARGIN 153

  , we quantify de denudation history of the onshore domain of the African Equatorial margin (Source study), in order to compare denudated volumes with that of the sediments accumulated on the margin (Chapter 5) by taking into account the evolving paleogeographic evolution of the onshore domain(Ye et al., submitted).Two commonly used ways exist for quantifying erosion providing clastic sediments that fill sedimentary basins: mapping relict paleolandsurfaces of known age and thermochronological analyses. Study of paleolandsurfaces characteristic of West Africa has been carried out by[START_REF] Grimaud | Dynamique long-terme de l'érosion en contexte cratonique: l'Afrique de l'Ouest depuis l'Eocène[END_REF], which revealed the landscape evolution and denudation history during the Cenozoic. This method allows reconstructing ancient drainage systems and quantifying denudated volume at fairly high-resolution spatial and geological temporal scales (1-10 Ma / 10-1000 km). In this study, we focus on the pre-Cenozoic denudation history in West Africa, by using low-temperature thermochronology (AFTA, Apatite (U-Th-Sm)/He), which reveals the exhumation and burial histories of the first 3-4 km of the continental crust. The temporal resolution of this approach is relatively low, but it allows for a first-order quantification of denudation. Sampling was carried out along three transects from Guinea to Benin, two of which were sampled by D. Chardon, D. Huyghe and D. Webster in 2014. A third transect in Ivory Coast was established by samples donated by A. Kouamelan used in his PhD work

(

  AFTA) at the School of Geographical and Earth Sciences, University of Glasgow. In this chapter, I will present the main outcomes of the thermochronological study in terms of ages and thermal history models. Denudation histories along each transect were computed on the basis of temperature-time paths obtained by inversion of the data assuming a constant thermal gradient of 25°C. Denudated volumes and denudation rates were quantified by an common phosphorous-bearing accessory mineral [Ca5(PO4)3(F,Cl,OH)], found in the Earth's crust. Uranium and thorium are important trace elements in apatite. Three isotopes exist in natural uranium-bearing minerals: 238 U, 235 U and 234 U. The dominant 238 U with an abundance of 99.3 % experiences nuclear decay by two processes: spontaneous fission which allows apatite fission-track analysis, and Į-decay (emission of a 4 He nucleus) on which apatite (U-Th-Sm)/He dating is based. of fission tracks Fission tracks occur as a result of spontaneous fission of uranium atoms (principally 238 U) which splits uranium nucleus into two fragments. They are considered as radiation-damage trails when positively charged fragments repel each other through the lattice with large amount of liberated energy (Figure 6-1). Fission tracks found in natural samples are called 'spontaneous tracks' or 'latent tracks'. They can be selectively enlarged by an acid etchant, such as HNO3 solution for apatite.

Figure 6 - 1

 61 Figure 6-1 Formation of fission tracks in three steps. (a) Trace amounts of unstable radioactive 238U are present in the crustal lattice (dark circles). (b) Spontaneous fission of 238 U produces two highly charged heavy particles with mass numbers in the ranges of 85-105 and 130-150. They repel each other and interact with other atoms in the lattice by

  decay constant for 238 U, 1.55125x10 -10 yr -1 Ȝf = spontaneous fission decay constant for 238 U I = isotopic ration 235 U/ 238 U, 7.2527x10 -3 ı = thermal neutron cross-section for 235 U, 580.2x10 -24 cm -2 ij = thermal neutron fluence ȡs = spontaneous track density ȡi = induced track density g = geometry factor for spontaneous fission track registration The zeta calibration (ȗ) is used for eliminating unknown parameters in Equation (1), such as the value of the decay constant for spontaneous fission of 238 U (Ȝf) and the thermal neutron fluence (ij) used to induce fission of 235 U. The thermal neutron fluence (ij) is related to the track CHAPTER 6 :CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 159 density in the mica (the external detector, see below) (ȡd) by : ߶ ൌ ɏ ୢ , where the B is a constant calibration factor.

Figure 6 - 3

 63 Figure 6-3 Predicted track-length reduction with time for different thermal histories with a continuous heating (a), a continuous cooling (b), a rapid cooling (c) and a heating/a cooling (d). The length reduction trajectories and tracklength distribution are calculated with the annealing model of Laslett et al. (1987) (after Gallagher et al., 1998).

CHAPTER 6 :

 6 Figure 6-4 Cartoon representing of the effects of implantation, ejection and inclusions during alpha-ejection (Wildman, 2015).

Figure 6 - 5

 65 Figure 6-5 Left hand figure shows the structure of the theoretical PAZ and PRZ beneath a flat topography and the expected age profile with depth for both AFT and AHe thermochronomters. Asterix and star represent samples currently at depth. Right hand figure shows these samples now exhumed following a period of rapid uplift and denudation producing high relief topography. The high relief topography perturbs the present day PAZ and PRZ at depth. In high relief areas the age profile may have preserved the structure of the profile through the now exhumed

Figure 6 - 6

 66 Figure 6-6 Comparison of determined thermal histories by both AFTA and AHe methods (A), only AFTA (B) and only AHe dating (C). All thermal histories are compatible with thermochronological data and have been modelled by

Figure 6 - 7

 67 Figure 6-7 Location of earlier published low-temperature thermochronological data (AFTA and AHe) from Bouillin et al. (1998), Clift et al. (1998), Gunnell (2003), Bigot-Cormier et al. (2005), Cavellec (2006), Rougier et al. (2013), Leprêtre (2015), English et al. (2016), and new samples along three transects in Guinea-Benin. Quaternary sand was removed from the simplified geological map.

  20 samples were collected along a transect from Conacry to Bamako by D. Chardon, D. Huyghe and D. Webster in 2014 (Figure 6-8). The transect is 700 km long and covers a range of altitude from 0 to 1200 m. The space between samples is of 40-50 km, except an empty zone from the Eastern Guinea to the Southern Mali, due to poor outcorp conditions.

Figure 6 - 8

 68 Figure 6-8 Guinea sample locations on the tectonic map of Milesi et al., (2010) (Provided by D. Chardon).

  (Université Félix Houphouêt-Boigny, Cocody, Ivory Coast) that have been collected during his PhD work for the purpose of a U-Pb geochronological study (Figure 6-9, Kouamelan, (1996)). They were mostly heavy mineral separates comrising apatites, which are suitable for thermochronological analysis (AFTA and AHe dating). The spatial distribution of the samples forms a wide latitudinal corridor covering a range of 0-471 m in elevation. Most samples are granodiorites and gneisses which yielded a large amount of apatites. More details on Ivory Coast samples are summarized in Appendix 4.

Figure 6 - 9

 69 Figure 6-9 Ivory Coast sample locations on the geological map of Ivory Coast.

Figure 6 -Figure 6 -

 66 Figure 6-10 Benin sample locations on the geological map of Benin.

Figure 6 -

 6 Figure 6-12 Plot of AFT ages against elevation (left) and mean track lengths (MTLs) against AFT ages (right) of three transects. AFT ages are Central AFT ages with 1ı standard error, as well as MTLs (Provided by M. Wildman).

Figure 6 -

 6 Figure 6-13 Measured Central AFT ages (top left) and mean track lengths (top right) with uncertainties in Ivory Coast plotted on a topographic map (Provided by M. Wildman).

Figure 6 -

 6 Figure 6-14 Measured AFT ages (top left) and MTLs (top right) in Benin localized on a topographic map and a plot of topography, AFT ages and MTLs of two Benin transects (bottom) (Provided by M. Wildman).

Figure 6 -

 6 Figure 6-15 Distribution of AFT ages (top) and mean track lengths (bottom) of the study area, after narrow interpolation of three TS2P transects and additional Guinea and Burkina Faso data (Provided by M. Wildman).

  . A posterior probability distribution of the model parameter values given the data can be constructed by calculating: Pሺܯȁܦሻ=PሺሺܯሻሻPሺܦȁܯሻ Where P (M|D) is the posterior probability density function of the model parameters given the data; P(D|M) is the likelihood probability function of obtaining the data given the model and P(M) is the prior probability density function given to the model. CHAPTER 6 :CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 180

  Ma), Mid-Late Jurassic (175 -145 Ma), Early Cretaceous (145-100 Ma). Spatial distribution of thermal histories and cooling rates were evaluated. Early Jurassic (200 -180 Ma): Slow cooling Interior samples (GN6 -GN10) at 100 -225 km distance from the coastline record cooling beginning in the Early Jurassic and continuing until the Cenozoic in an almost linear manner (Figure 6-16

  Mid-Late Jurassic (175 -145 Ma): Slow to Rapid Cooling Mid-Late Jurassic cooling event was recorded by samples landward of the above mentioned samples (GM12 and GM14, Figure6-16). GM12 was cooled rapidly at a rate of 3.0 °C/Myr from 110 ± 20°C at c. 175 Ma to near surface conditions at c. 120 Ma. However, GM14 recorded a slow cooling at 0.6 °C/Myr which lasted for c. 160 Myr.Early Cretaceous (145-100 Ma): Moderate to Rapid Cooling Coastal samples (GN1, GM2 and GN3) at less than 50 km of distance from the coastline experienced cooling beginning in the Early Cretaceous (Figure6-16). GM2 recorded a rapid cooling at c. 3.00 °C/Myr, which rapidely brought the sample under near surface conditions. However, GN1 and GN3 recorded a continuous cooling until the Cenozoic with a cooling rate of c. 1.8 °C/Myr. The timing of this cooling would fit with the rifting of the Guinea-Liberia margin which initiated during the. This means rifting affected the onshore domain only on a narrow coastal strip (less than 50 km from the coastline). An interior sample (GM13) also recorded Early Cretaceous cooling at a rate of c. 1.8 °C/Myr, which probably suggests another local tectonic event and needs further investigations.

Figure 6 -

 6 Figure 6-16 T°C/ time modelling results of samples projected on the Guinea transect in Ivory Coast. Only AFT data and geological constraints were used for modelling. The onset of cooling of each model during three time periods is indicated. Thermal models were produced and provided by M. Wildman.

CHAPTER 6 :

 6 CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 183 Early Jurassic (190 -170 Ma): Extremely Slow Cooling Samples which recorded cooling beginning in the Early Jurassic occupy large areas between 100 to 400 km inland of the coastline (Figure 6-17). The cooling is extremely slow in a linear manner until the present day with a cooling rate ranging from c. 0.2 to 0.5 °C/Myr. The temperature is estimated at the beginning of the cooling to be 110 ± 10°C for SOK1A and DLO3 Bis. However, northerner samples (SEN-1 & MK-64) record a cooling at 50 °C/Myr at the same time following an earlier more rapid cooling whose initial conditions are unconstrained. Mid-Late Jurassic (170 -150 Ma): Slow cooling Samples (KG33a, VAA-1 and BEZ-1) on the northern part of the transect recorded slightly faster cooling than those described above during the Mid-Late Jurassic. They have cooling rate of c. 0.6-1.6 °C/Myr (Figure 6-17). This cooling initiates at a temperature of 110 ± 10°C at c. 160 Ma. KG33a recorded a change in cooling rate from 0.3 to 1.6 °C/Myr at c. 110 Ma, which differs from the continuous cooling recorded by VAA-1 and BEZ-1 until the present day. Early Cretaceous (140-130 Ma): Rapid Cooling Rapid cooling was only recorded by near coast samples (SA-3 and SA-14) during the Early Cretaceous with a cooling rate of c. 3.0 °C/Myr (Figure 6-17). Near surface temperature was reached shortly after this rapid cooling event and have been maintained for 100 Ma. The timing of this cooling coincides with the rifting of the margin during at the latest the Barremian (c.130 Ma).

Figure 6 -

 6 Figure 6-17 T°C/ time modelling results of samples projected on an N-trending transect in Ivory Coast. The onset of cooling of each model during three time periods is indicated. Thermal models were produced and provided by M.

CHAPTER 6 :

 6 CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 185 Resulting thermal histories show great variabilities in terms of cooling onset time and cooling rate. Despite the variabilities, three major time periods of the onset of cooling were still observed: Mid-Late Jurassic (170 -150 Ma), Early Cretaceous (140 -120 Ma), Paleogene (40 -20 Ma). Mid-Late Jurassic (170 -150 Ma): Slow Cooling A cooling event during the Mid-Late Jurassic was only observed on the northernmost sample (BN-6, Figure 6-18). It is characterized by a slow cooling rate of 1.4 °C/Myr at c. 160 Ma. Near surface temperature was reached at c. 100 Ma and was maintained until the present day. Early Cretaceous (140-120 Ma): Slow to Rapid Cooling The Early Cretaceous cooling event was recorded by samples near the coastal basin (BN-1 to -5, and -17). Between them, a first group (BN-1, -2, -3 and -17) encompassing a great distance along the transect (100-250 km) is characterized by a slow cooling rate of 0.5 °C/Myr with unconstrained initial conditions (Figure 6-18). A second group (BN-4 and -5) recorded a cooling event of 2.0 °C/Myr from c. 140 to 110 Ma (initiated at 110 ± 10°C). This cooling is comparable to the Early Cretaceous cooling event observed in Ivory Coast along a c. 50 km wide coastal strip. The difference between these two Early Cretaceous cooling events is the position of the samples which are located farther inland in Benin (> 300 km from the coastline), probably due to the denudation of the embayment that had a greater extent at the time. Paleogene (40-20 Ma) A recent cooling event was recorded by samples (BN-7, -8, -9 and -10) near the Kandi basin (Figure 6-10), which started near the surface at c. 50 °C during the Paleogene and brought the samples to the surface until the Miocene (Figure 6-18). The samples probably experienced burial during the Late Cretaceous when the Kandi basin was actively subsiding, before being exhumed in the Cenozoic. CHAPTER 6 :CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 186 Other samples (BN-11, -12 and -18) were revealed to be at a shallow depth (80-50 °C) at c. 200 Ma and experienced extremely slow cooling (c. 0.2 °C/Myr) until the present-day (Figure 6-18). The beginning of the cooling could be much older for BN-11 and -12. The thermal history of BN-18 (Upper Cretaceous sandstone) is much more problematic, as it was submitted to possible complex burial and exhumation history within the coastal basin since the Upper Cretaceous.

Figure 6 -Figure 6 -

 66 Figure 6-18 T°C/ time modelling results of samples along the Benin transect. The onset of cooling of each model during three time periods is indicated. Thermal models were produced and provided by M. Wildman.

Figure 6 -

 6 Figure 6-20B, Figure 6-21). This potentially increased the volumes by giving high values along the coastline and the inland boundary. The resulting volumes were so to be the maximum. A second set of surfaces was established as an end-member by fixing the denudation values to zero at the boundary (Figure 6-20C, 6-20D and Figure 6-22). The resulting volumes were decreased significantly and considered as the minimum values. Uncertainties in the volumes presented below are constrained by the difference between maximum and minimum volumes issued from each configuration (free or zero-value boundary condition).

x

  -20, Figure 6-21 and Figure 6-23), common general trends were observed: x Denudation was systematically low (mostly < 1000 m) during the interval going from the Early Cretaceous (140 -120 Ma) to the Neogene-Quaternary (25 Areas with relative high and low denudation values did not significantly evolve since the Jurassic (200 -0 Ma). High values were concentrated at three regions CHAPTER 6 :CONTINENTAL DENUDATION HISTORY: LOW-TEMPERATURE THERMOCHRONOLOGY 192 close to the boundaries, in the West (Guinea), the South (Western Ivory Coast)and East (Benin);x A narrow corridor of intense denudation exists along the Western coastline of Ivory Coast between 140 and 100 Ma and disappears afterwards. We interpret this corridor to reflect Early Cretaceous rift shoulder topography that was eroded after the continental breakup.

Figure 6 -

 6 Figure 6-21 Maximum denudation maps from 140 to 0 Ma obtained by triangulated surface construction under a free boundary condition. Note that duration varies between time intervals.

CHAPTER 6 :

 6 Figure 6-23 Diagrams showing the results of denuded volume (A), denudation rate in m 3 /Ma (B) and in m/Ma (C) from 200 to 0 Ma.

Figure 7 - 1

 71 Figure 7-1 Middle Eocene -recent (45 -0 Ma) volumetric source-to-sink budget. (A) Map of paleo-drainage divides at 45 and 24 Ma over a topographic map of West Africa. Arrows with the same color indicate general draining direction of three major drainage areas at 45 and 24 Ma. Clastic export rates and accumulation rates are shown for three sourceto-sink systems: (B) the Short Atlantic drains and the Sierra Leone-Liberia basin, (C) the Long Atlantic drains and the Ivory Coast and the Ghana-Benin basins, and (D) the Niger catchment and the Niger Delta.

  -9 to Figure3-11) suggest that the area covered by thermochronological sampling roughly coincides with the area that was being eroded during the Cretaceous i.e., at the emplacement of the currently outcropping Léo-Man shield. Only non-extrapolated accumulation rates were used, due to the same raison as above. But volumes under-estimination is less important for the Late Cretaceous because the main depocenters were close to the shoreline and therfore included in the non-extrapolated volumes (e.g., Chapter 5). CHAPTER 7 :OUTLINES OF A SOURCE-TO-SINK ANALYSIS, IMPLICATIONS FOR VERTICAL DISPLACEMENTS OF THE MARGIN 201

  Cretaceous. The sedimentary volumes between the West African continental sources and the Equatorial Atlantic basins' sinks are therefore balanced within uncertainties. However, at a higher resolution, an excess of accumulated volume and rate occurred during the Cenomanian-Santonian (100 -85 Ma) and the Campanian-Maastrichtian (85 -65 Ma). Paleocene-Early Eocene (60-45 Ma) denudation rate in West Africa exceeds the accumulation rate in the Equatorial Atlantic basins (Figure 7-2 and Table 7-2).

Figure 7 - 2

 72 Figure 7-2 Late Cretaceous -Early Eocene (100 -45 Ma) denudation and accumulation. (A) Cenomanian-Santonian denudation map (100 -85 Ma, Figure 6-21) and Upper Cenomanian paleogeographic map (97 -93 Ma, Figure 3-9) overlapping on the topographic map of West Africa. Arrows indicate potential draining directions of eroded materials. Denudation rate in West Africa (B) and accumulation rates in the Equatorial Atlantic basins (C) are shown.

CHAPTER 7 :

 7 OUTLINES OF A SOURCE-TO-SINK ANALYSIS, IMPLICATIONS FOR VERTICAL DISPLACEMENTS OF THE MARGIN203observed on seismic data from offshore Ivory Coast to Nigeria since the Late Miocene[START_REF] Huyghe | Forçage des liens source-marge au Cénozoïque (marge Bénin-Sénégal[END_REF].The Late Cretaceous-Early Eocene (45-24 Ma) sediment budgets are balanced considering total eroded and deposited volumes. The excess of denudation during the Paleocene-Early Eocene (65-45 Ma) compared to offshore accumulations is more problematic. But the thermochronologyderived denuded volumes should be converted into clastic exported volumes by taking into account of the regolith porosity (as done for the 45-0 Ma period) and the potentially different geometry of the drainage system, as it has been done for the 45-0 Ma period. A second source for the sourceto-sink discrepancy could be due to the fact that the accumulated volumes are non-extrapolated to distal basin (Chapter 5). Because the Equatorial Atlantic Ocean was fully opened during the Cenozoic and more sediments were deposited in distal plain, the accumulation is therefore underestimated.The "excess" of accumulated volumes during the Late Cretaceous could have several causes.Lower Cretaceous syn-rift sediments exposed on the shelf of the margin could have been eroded and re-deposited on the slope of the margin and the distal basin. On seismic data, Cenozoic sediments rest directly upon the Late Albian breakup unconformity (Figure4-4a and 4-8). Vitrinite reflectance data available in wells on the shelf of the margin show 500 -1000 km of erosion during the Late Cretaceous hiatus (M. Dall'asta, personal communication). This supports erosional remobilization of Lower Cretaceous sediments or earlier Upper Cretaceous deposits. Moreover, mass-transport deposits and turbiditic systems were observed on seismic data in the Upper Cretaceous series (Chapter 4), which further support the remobilization hypothesis. Another cause for this discrepancy would be the existence of an extra source of eroded sediment. According to our paleogeographic maps(Ye et al., submitted), since the opening of the Equatorial Atlantic Ocean during the Late Albian, the area located South of the Benue Through was exposed to erosion and contributed sediments in the Atlantic Ocean. The paleogeography study further showed that Cretaceous sediments issued from the erosion of the marginal upwarp were temporarily stored in the Saharan intracratonic basin. Part of these sediments has been re-eroded and transported to the Equatorial Atlantic margins by river(s) crossing the upwarp. As the Saharan basin always lies outside the area covered by the thermochronology study (Figres 6-9), such sediment transfers may have contributed to the "extra" volume now found in the margin basins. CHAPTER 7 :OUTLINES OF A SOURCE-TO-SINK ANALYSIS, IMPLICATIONS FOR VERTICAL DISPLACEMENTS OF THE deposition loading can cause uplift and subsidence, in response to the isostatic flexure of lithosphere. In order to simulate such vertical displacements induced by sediment mass transfers documented by the present study, we used a numerical modelling approach (Flex3D) applied to the Ivory Coast case where two margin types, transform and divergent, are present (Chapter 4). The two configurations were tested separately and combined with the onshore 2D denudation transect (Chapter 5).

  calculates the flexural response of the lithosphere subjected to an instantaneous stretching that represents rifting. It incorporates the thermal relaxation following stretching and diffusion-type surfaces processes. The surface deflection can be calculated, assuming a thin elastic plate, whose effective elastic thickness (EET) is controlled by a given isotherm. The lithospheric stretching parameters (REF) are defined as follows. For the lithosphere, į = h 0 m/hm, and for the crust, ȕ = h 0 c/hc, where h 0 m and h 0 c are initial thicknesses of the lithosphere and crust, and hm and hc are thickness of the lithosphere and crust at the end of the stretching.

( 6 )

 6 Figure 7-3 Location of the thermochronological denudation transect and seismic profiles in Ivory Coast used for modelling of vertical movements of Coast Ivory transform and divergent margins. T1: Seismic profile used for transform margin; D1: Seismic profile used for divergent margin.

Figure 7 -

 7 4a and c) superimposes over the uplift profile resulting from the combination of denudation and offshore loading (purple line, Figure7-4a and c).Importantly, the onshore uplift pattern is comparable for the transform and the divergent margins although they have different necking widths and sedimentary histories. The same uplift profiles were obtained that are mostly controlled by the denudation pattern. The corridor of highest uplift closed to the shoreline between 140 and 100 Ma may correspond to the flexure-controlled rift shoulder formed and eroded during the syn-rift stage despite the very narrow zone of necking expected in a transform regime. The eroding coastal topography was not maintained later during the Late Cretaceous and Cenozoic as long-wavelength "cratonic" deformation may have exerted a growing influence on the cooling margin. Longer wavelength continental flexure may explains the attenuated inland uplift pattern.

  Fig 9

  Fig 7

  Fig 1

  Fig 9

.1. Ouverture de l'Atlantique Central

	CHAPTER 2 :CONTEXTE GEOLOGIQUE DE L'AFRIQUE DE L'OUEST
	x ECMA (East Coast Magnetic Anomaly) et WACMA(West African Coast Magnetic
	Anomaly) premièrement défini par Sahabi et al. (2004) sont considérés étant la limite
	océan/continent. Son âge Sinémurien Inférieur (190 Ma) représente le moment de la
	création de la première croûte océanique (Breakup) qui est basé sur l'âge des dépôts
	salifères synrifts (Formation d'Eurydice/Argo en Nouvelle Ecosse et d'Argana au
	Maroc, Figure 2-17).
	L'Océan Atlantique s'est mis en place progressivement durant le démantèlement de la
	Pangée depuis le Trias Supérieur, en formant les marges passives Africaines et Américaines. La
	reconstitution cinématique de l'ouverture de l'Atlantique, surtout l'Atlantique Central et
	Equatoriale est nécessaire pour comprendre l'évolution de la marge Ouest Africaine. Il existe de
	nombreux modèles de reconstitution cinématique dont les plus récents montrent qu'en effet,
	l'ouverture de l'Atlantique s'est fait en plusieurs stades successifs associés souvent avec des
	événements magmatiques.
	2.4L'Atlantique Central est limité au Nord par la zone de fracture de Pico et Gloria et au Sud
	par la zone de fracture de 15°20' et Guinéenne (Figure 2-16). De nombreux modèles proposés par
	différents auteurs tentent de reconstruire l'évolution cinématique depuis son ouverture. En effet, la
	phase initiale de l'ouverture de l'Atlantique Central reste débattue. Son histoire depuis 120Ma
	(Chron M0) est relativement mieux contrainte grâce à la présence des linéaments des anomalies
	magnétiques remarquables et des zones de fracture océaniques. Il existe de différents modèles
	désignant l'ouverture avec ou sans saut de ride océanique (Ridge jump). Le modèle le plus récent
	de Labails et al. (2010) suggère que l'ouverture de l'Atlantique Central, sans saut de ride océanique,
	débute au Jurassique Supérieur (190 Ma). Il est basé sur l'analyse des données géophysiques
	récentes (magnétiques, gravimétriques et sismique) et la géologie continentale.
	Quatre linéaments des anomalies magnétiques conjugués ont été identifiés (Figure 2-16,
	Labails et al., 2010) :
	52

  Le segment austral est séparé du segment de Falklands par la zone de fracture d'Agulhas-Falkland. On trouve des SDRs (Seaward Dipping Reflectors) sur les marges du segment austral qui indiquent qu'elles seraient volcaniques de ces marges (Figure 2-19). Le segment de

	CHAPTER 2 :CONTEXTE GEOLOGIQUE DE L'AFRIQUE DE L'OUEST
	sur les deux côtés.
	Le démantèlement de la Pangée continue au Crétacé Inférieur (120 Ma) dans l'Atlantique
	Sud, l'Atlantique Nord et autour du continent Antarctique. L'Atlantique Sud s'est ouverte en effet
	sur la zone de suture Panafricaine entre les continents Sud-Américain et Africain.
	L'Atlantique Sud peut être divisé en trois segments : le segment central, le segment austral
	et le segment des Falklands (Figure 2-19). On différencie ici le segment équatorial des autres
	segments comme étant l'Atlantique Equatorial. Le segment central est séparé du segment
	équatorial par la zone de fracture d'Ascension au Nord et du segment austral par la zone de fracture
	de Rio Grande au Sud. Le long du segment central, se localise un grand bassin Aptien d'évaporites
	56

PAPER 1 -Paleogeographic and structural evolution of northwestern Africa and its Atlantic margins since the Early Mesozoic Jing Ye 1,2 , Dominique Chardon 1 , Delphine Rouby 1 , François Guillocheau 3 , Massimo Dall'asta 2 , Jean-Noel Ferry 2 , Olivier Broucke 4

	Le rifting de l'Atlantique Equatoriale s'est propagé d'Ouest en Est depuis l'Atlantique
	c) 84 Ma Centrale, et du Valanginien (140 Ma) à l'Aptien (112 Ma), sous la forme d'un système en-échelon
	« rift-transformante ». Sa connexion au système de rift continental permet de définir un nouveau
	modèle cinématique syn-rift constitué de six microplaques impliquant le nord-ouest du continent
	africain. La reconstruction des structures syn-rift a également permis d'affiner la configuration pré-
	ouverture entre l'Afrique et l'Amérique du Sud. Les cartes révèlent la présence et le maintien des
	bourrelets topographiques le long de la marge continentale. L'érosion de ces bourrelets a alimenté
	non seulement les bassins des marges équatoriales, mais aussi un grand bassin intracratonique qui
	a fonctionné comme une zone de stockage temporaire de sédiments. Ces sédiments méso-
	cénozoïques ont en effet pu être transférés vers la Téthys (au Nord) ou vers l'Océan Atlantique
	Equatoriale (au Sud). Le schéma morpho-sédimentaire est de plus compliqué par le bombement
	Géosciences Environnement Toulouse, Université de Toulouse, CNRS, IRD, UPS, CNES, F-topographique du point chaud du Hoggar qui a mené à la fragmentation tardive du bassin
	31400, France intracratonique en petits dépôt-centres résiduels. En liant l'évolution à grande échelle de l'Afrique
	nord-occidentale à celle de ces marges continentales, notre travail ouvre de nouvelles perspectives
	TOTAL R&D, Frontier Exploration, CSTJF, Avenue Larribau, F-64018 Pau Cedex, France sur les l'interférence entre déformation à grande longueur d'onde et transferts de sédiments,
	notamment pour les systèmes source-to-sink de type craton-marges.
	Géosciences Rennes, Université de Rennes 1, CNRS, CS 74205, 35042 Rennes Cedex, France
	TOTAL E&P, Middle East and North Africa -Technical Excellence, La Defense, Paris, France
	Les déformations intra-plaques ne sont pas vérifiées
	quantitativement avec des observations géologiques. Ces points doivent être améliorés dans le futur.
	Manuscript submitted to Geosphere

  -3a). The resulted track-lengths have a short mean value. The fission track age does not represent any discrete event. In contrast, a continuous cooling will shorten fission tracks produced through time to different degrees. The final track-lengths are characterized by a negatively skewed length distribution (Figure6-3b). The resulted fission track age tends to be younger than the onset of cooling. The lower probability of shorter tracks intersecting the etched surface results in lower measured fission track age. Only when minerals cooled rapidly and fission tracks did not have enough time to be annealed and stay relatively long, fission track ages can be considered approximately as those of the onset of cooling (Figure

Table 7 -

 7 1 45-0 Ma clastic export and accumulation budgets of the three West African source-to-sink systems (e.g., the

	CHAPTER 7 :OUTLINES OF A SOURCE-TO-SINK ANALYSIS, IMPLICATIONS
	FOR VERTICAL DISPLACEMENTS OF THE MARGIN

  Cette thèse présente une nouvelle approche de l'évolution paléo-géographique, structurale et sédimentaire de l'Afrique de l'Ouest et de sa marge atlantique équatoriale dans une perspective source-to-sink. Une nouvelle série de reconstructions paléogéographiques et structurales mésocénozoïques a été produite sur la base d'une méthode innovante. Elle permet de proposer, outre un nouveau modèle structural et cinématique d'ouverture précoce de l'Atlantique Equatorial, une histoire intégrée terre-mer de la déformation lithosphérique à grande longueur et des transferts sédimentaires associés. Une synthèse de la structure et de l'architecture stratigraphique post-rift crétacée supérieure de la marge Atlantique Equatoriale a été réalisée à partir de l'interprétation de données inédites de subsurface. Elle a permis de quantifier ensuite les volumes sédimentaires clastiques accumulés dans les bassins de la marge. Ce travail a également incorporé de nouvelles La segmentation longitudinale de la marge atlantique équatoriale a été systématiquement étudiée du point de vue de son orientation, de la largeur de sa zone de necking et de son architecture stratigraphique crétacée supérieure (immédiat post-rift). La géométrie de ce prisme stratigraphique varie selon la largeur de la zone de necking et les mouvements verticaux post-rift subis par les segments de la marge. Les sédiments proximaux crétacés supérieurs ont été seulement préservés sur la plateforme des segments de marge divergents, mais sont absents des segments transformants.Cette différence s'explique par des histoires différentes de mouvements verticaux post-rift des segments transformants et divergents. La plateforme des segments transformants a été probablement plus soulevée et plus longtemps durant le Crétacé Supérieur alors que seul un faible évènement d'érosion Santonien est enregistré par les segments divergents.L'histoire de la dénudation déduite de la thermochronologie montre des taux d'érosion à l'échelle de la zone d'étude relativement constants dans le temps de l'ordre de 9 m/Ma, typiques des cratons. La seule exception à cette homogénéité est une phase initiale un peu plus rapide en lien avec l'érosion de reliefs issus du rift localisé sur une bande côtière.

	Map
	Reference	Adegoke et al. 1986
	Method	Radiometrical	dating
	Age (Ma)	41
	constituent ainsi que des petits dépôt-centres résiduels. La portion de bourrelet marginal équatorial correspondant à l'affleurement actuel du craton ouest africain est la seule à être soumise à l'érosion depuis le pré-rift (ce qui est confirmé par les résultats thermochronologiques). Cet affleurement La nouvelle méthode de reconstruction paléogéographique et structurale développée dans le cadre de cette thèse pourra être appliquée dans d'autres contextes comparables. Les caractères Emplacement mode Intrusion in Kerri-Kerri formation
	coïncide avec une grande province de magmatisme kimberlitique pré-rift qui pourrait être à structuraux et stratigraphiques de la marge transformante ouest africaine qui contrastent largement
	l'origine d'une modification du manteau (métasomatisme) et acquérir ainsi une plus grande flottabilité que les domaines environnants. de ceux des marges divergente pourraient être comparés avec d'autres marges transformantes dans le monde. La comparaison avec sa marge conjuguée sud-américaine devrait s'avérer de ce fait être très prometteuse. Ignous Province or Location Benue Trough
	Country	Nigeria

données thermochronologiques basse-température acquises sur le domaine continental qui ont permis de caractériser l'histoire de l'érosion et de quantifier les volumes sédimentaires exportés depuis le Mésozoïque. Un bilan volumétrique source-to-sink a ensuite été réalisé.

Les domaines en érosion et en sédimentation en Afrique de l'Ouest évoluent depuis le début du rifting du futur Océan Atlantique Equatoriale. Un grand bassin continental saharien recevait les produits d'érosion du bourrelet marginal équatorial et communiquait vers l'aval (au Nord) avec la Téthys. Il a été ensuite envahi par la mer durant les transgressions crétacées supérieures et a pu, à plusieurs reprises, perdre des sédiments qui ont été re-exportés vers les bassins de la marge équatoriale. Les bassins intracratoniques actuels n'ont acquis leurs géométries qu'à partir de la fragmentation oligocène du bassin saharien par le percement du bombement du Hoggar, et ne L'analyse source-to-sink des volumes de dénudation et d'accumulation montre que l'ordre de grandeur des volumes érodés correspond à celui des volumes déposés durant le Crétacé Supérieur et le Cénozoïque. La réorganisation des systèmes de drainage à l'Oligocène Supérieur s'est exprimée par une augmentation de flux sédimentaire dans les bassins de la marge équatoriale. Des excès d'accumulation ont été détectés au Crétacé Supérieur et depuis le Miocène Supérieur qui peuvent s'expliquer par le stockage temporaire de sédiments dans le bassin intracratonique ou sur la plateforme de la marge. La réponse en isostatie flexurale de la marge aux transferts terre-mer de sédiments a été estimée dan le cas du segment ivoirien. Les mouvements ainsi générés correspondent à un soulèvement moyen cumulé à terre de l'ordre de 1200 m sur 600 km de distance dans les terres et une subsidence offshore maximum de plus que 4000 m à 100-200 km de la côte.

Le type de marge (transformante ou divergente) n'influence pas la quantité du soulèvement à terre.

Appendix 2. Compilation of thermochronological data (AFTA and AHe) available over Northwestern Africa.

  Sample's name, location, lithology, age and mean track length issue from AFTA, age of AHe dating and used reference are shown for each sample, when available.

	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Reference		Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015	Leprêtre, 2015
				396-96	81-38	133-40		234-32	222-138		326-104	384-166	87-41	81-27	185-94		111-43	67-29	95-47	52-14		82-63	93-52	101-35	92-24	AHE_Cor 80-27	rec	(Ma)	191-166			167-133
				280-67	66-31	99-31		178-26	175-99		256-88	277-120	61-27	65-21	138-62		77-35	55-23	74-38	39-12		64-55	71-42	77-28	71-35	AHE_Mean 67-21	(Ma)	162-137			142-86
	2,0	1,6	1,6	2,3		1,7	2,1	2,3	2,1	1,9			1,8	1,8		1,8	2,0	1,6	1,8		1,8	1,9	1,7	1,8	MTL_	Std	1,8	1,7	2,1	1,8
	0,3	0,2	0,2	0,2		0,2	0,2	0,3	0,4	0,2	0,0		0,2	0,3		0,2	0,3	0,2	0,2		0,2	0,4	0,3	0,3		Error		0,2	0,2	0,2	0,3
	11,7	12,4	12,0	12,3		12,0	11,5	11,5	11,2	11,5	0,0		11,8	12,2		12,5	9,4	11,9	11,8		12,2	11,2	10,7	12,1	MTL	(μm)	11,9	11,9	12,4	11,4
	13	13	14	21	21	21	26	24	25	27	36		8	6	10	7	8	6	8	12	8	13	15	11	16	Error		9	8	10	8
	172	199	202	256	237	264	307	315	355	359	393		107	115	118	126	127	128	128	137	141	143	156	160	AFT_ 175	Age	(Ma)	139	150	163	166
	Microgranite	Granite	Granodiorite	Grabbro	Gabbro	Gabbrodiorite	Gabbrodiorite	Gabbrodiorite	Gabbro	Trondhjemite	Rhyolite	Gabbro	neph. syen.	Gneiss	Charnockite	Volcanite	Granite	neph. syen.	neph. syen.	Charnockite	Granite	Granite	Granite	Granite	Granite	Lithology		Granite	Granite	Gabbro	Monzogranite
	258	273	394	216	381	252	252	252	355	360	366	350	400	110	137	110	194	400	400	125	292	318	284	293	Elevation 282	(m)	305	252	236	384
	24,3 Reguibat Central	24,5 Reguibat Central	26,6 Reguibat Central	24,0 Reguibat Central	27,4 Reguibat East	25,6 Reguibat East	25,6 Reguibat East	25,6 Reguibat East	26,1 Reguibat East	25,5 Reguibat East	26,2 Reguibat East	25,6 Reguibat East	22,5 Reguibat West	21,0 Reguibat West	20,7 Reguibat West	21,0 Reguibat West	21,9 Reguibat West	22,5 Reguibat West	22,5 Reguibat West	20,7 Reguibat West	22,6 Reguibat West	22,6 Reguibat West	22,7 Reguibat West	22,6 Reguibat West	22,7 Reguibat West	Lat Location		24,9 Reguibat Central	24,0 Reguibat Central	24,1 Reguibat Central	26,5 Reguibat Central
	-10,0	-9,7	-7,1	-10,5	-3,2	-3,6	-3,6	-3,6	-3,0	-6,1	-6,2	-6,0	-14,3	-15,6	-13,4	-15,6	-15,1	-14,3	-14,3	-13,4	-14,5	-14,3	-14,5	-14,4	-14,5	Long		-9,9	-9,4	-10,5	-7,3
	TEN4065	TGH4072	A	AL10	TEN1153	TL3	CH2	CH1	CH3	DEG6	GH3	IG3	GH20	AOS2	TAS29	AG169	TAS233	TCH7	AOS3	AOS5	AG167	SC12	SC9	SC5	SC11	Sample SC15	Name SC-31	TGH3163	TGH3111	B	TEN1185	YT7

Table of the AFTA data

  BoiffoMedium grained, weathered sandstone (« Cambro-Silurian » of the « Kandi basin »). The outcrop is mainly made of coase-grained beds and gravels.The sampled layer shows slightly oblique stratifications. The sample is crucial although it may not be too favorable at first sight. It is the northernmost of the transect i.e., the closest to the southern margin of the Iullemmeden basin. « straight ») hornblende gneiss of TTG composition (U/Pb conventional age of ca. 540 Ma). Upper amphibolite facies deformation conditions. A few, highly sheared concordant leucocratic veins (the sample is devoid of melt). Some isoclinal folds. The main fabric reworks an earlier, shallowly dipping foliation. Wéré Pink weathered medium size grained sandstones (« Cambro-Silurian »). The sampled layer is the finest grained in an outcrop of conglomerates and heterogeneous coarse-grained sandstones. Oblique stratifications in the sampled bed. Bedding: N25, 35W. NE piedmont of a small inselberg. Migmatitic, banded hornblende (TTG) gneiss (comparable to BN 7, but with clearer evidence of melting and melt remobilization, maybe due to lesser strain). Late C' shear bands (dextral). BN 10 10.37225 2.72320 345 Gneiss Road cut ca. 13 km N of Bembéréké Migmatitic granitic augen gneiss (melt collection in concordant veins and individualization of phenocrysts in those veins). (age, mean track length, number of measured track lengths, standard deviation, Dpar, and the person who operated). Provided by Mark Wildman.

	APPENDIX	3,6 IC-GN marginal ridge sandstone, claystone, limestone Bouilin et al., 1997;Clift et al., 1998 VAA-1 7,41133 6,63650 270 granodioritic gneiss IC-GN marginal 959 -2,7 3,6 ridge Sandstone Clift et al., 1998 1.5 km SE of Vaafla Same as BEZ-1 197 biotite migmatitic LOG-2 7,05867 7,52883 269 gneiss Logoualé village, 6 km E of Douonfapleu Core of the Logoualé "band". Millimetric layering (more rarely centimetric). Foliation: N70. 47 Road , N of BN 7 2.7 km E of Bïtapia, 6.7 DLO3bis 6,49950 6,45933 201 leucogranite W of Broma Intrusives in schists. Predominance of microcline. Muscovite & green biotite. 198 11.13767 2.90475 298 Gneiss Outcrops along the Kandi -Banikouara road, less than 1 km from the entrance circle of Kandi Banded (BN 8 SOK-1a 5,67650 6,64933 159 tonalitic gneiss 3.2 km SSW of Nibi II, 7.4 km NNW of Salékoragui Melanocratic 198 3.2 km SSW of Nibi II, 7.4 SOK-1b 5,67650 6,64933 159 tonalitic gneiss km NNW of Salékoragui Coarse grained, hololeucocratic. Occurrence of quartz and microcline megacrysts, rare FeMg minerals. 198 & 199 10.80048 2.80781 347 Sandstone Inselberg E side of the Guinea 350 sandstone Guinea 900 granite Guinea 1150 sandstone Guinea 850 diorite Guinea 770 gneiss Guinea 692 gneiss Guinea 465 granite Guinea 475 granite Guinea 500 amphibolite gneiss Guinea 864 granite Guinea 800 granite Guinea 700 granite Guinea 691 granite Guinea 27 Gniess Benin 160 Granitiod Benin 144 Gniess Benin 197 Granitiod Benin 302 Granitoid Benin 374 Granitiod Benin 238 Sandstone Benin 262 Gniess Benin 203 Sandstone Ivory Coast 270 Granite-gniess Ivory Coast 15 Granodiorite Ivory Coast 201 Leucogranite Ivory Coast 393 Granite-gniess Ivory Coast 295 Granodiorite Guinea GM14-02 (2) 8,86E+05 52,74 Guinea GM14-02(3) Guinea GM14-02 (4) 3,49E+05 33,54 Guinea GM14-02 (5) 5,92E+05 42,05 Guinea GM14-02(6) 6,05E+05 6,66 Guinea GM14-02(10) 2,21E+05 14,61 Guinea GM14-12 (1) 2,07E+05 12,96 Guinea GM14-12 (2) 2,15E+05 12,68 Guinea GM14-12 (3) 2,19E+05 14,45 Guinea GM14-12(4) 9,71E+04 12,70 Guinea GM14-12(13) 7,85E+04 10,54 Guinea Guinea gneiss BEZ-1 7,45900 6,16400 266 granodioritic 7.8 km E of Zanzra, 5.7 km W of Klazra Quartz, microline, plagioclase, green hornblende, biotite & euhedral allanite 197 BN 6 11.67882 3.19195 238 Sandstone Ferricrete-capped cuesta, 1km E of the Guinea 70 granite 255 sandstone Guinea 720 gneiss Guinea 545 gneiss Benin 268 Sandstone Benin 557 Sandstone Guinea GM14-01 (2) 1,08E+05 6,18 Guinea GM14-01(8) 6,47E+04 1,16 Guinea GM14-01(12) 1,45E+05 5,34 Guinea GM14-13(12) 5,54E+04 6,39 Guinea GM14-13(13) 1,06E+05 0,86 GM14-13(16) 1,64E+05 1,08 Guinea GM14-13(17) 7,25E+04 0,66 Guinea GM14-13(19) 1,02E+05 2,46 Guinea GM14-13(20) 2,15E+05 6,94 Guinea GM14-14(7) 2,39E+05 8,17 Guinea GM14-14(9) 1,53E+05 1,39 Guinea GM14-14(13) 1,26E+05 1,58 Benin BN2 (1) 4,01E+04 2,34 Benin BN2 (2) 5,08E+04 2,25 Benin BN2 (3) 3,59E+05 16,79 Benin BN2 (4) 3,78E+05 22,27 Benin BN2 (9) 8,87E+04 5,50 Benin BN3 (13) 2,22E+05 10,07 Benin BN3 (14) 3,00E+05 10,41 Benin BN3 (15) 8,40E+04 2,77 Benin BN3 (16) 1,10E+05 5,34 Benin BN3 (17) 4,41E+04 2,35 Benin BN3 (18) 3,23E+05 9,06 Benin BN3 (19) 3,71E+05 20,25 Benin BN3 (20) 2,32E+05 12,17 Benin BN3 (21) 1,93E+05 13,86 Benin BN3 (22) 1,14E+05 4,93 Benin BN3 (23) 7,80E+04 4,30 Benin BN4 (7) 7,68E+04 5,53 Benin BN4 (9) 1,72E+05 10,81 Benin BN4 (10) 9,24E+04 6,00 Benin BN7 (6) 5,65E+05 6,96 Benin BN7 (7) 9,36E+04 3,65 Benin BN7 (10) 2,37E+05 5,19 Benin BN7 (12) 1,71E+05 1,75 Benin BN7 (13) 1,29E+05 5,69 Benin BN7 (14) 1,06E+05 3,73 Benin BN7 (15) 4,06E+04 2,22 Benin BN7 (16) 7,14E+04 3,12 Benin BN7 (17) 2,51E+05 10,73 Benin BN7 (18) 1,41E+05 6,08 Benin BN7 (19) 4,66E+04 2,00 Benin BN7 (20) 1,27E+05 4,47 Benin BN7 (21) 2,48E+05 7,75 Benin BN9 (3) 2,56E+05 8,72 Benin BN9 (6) 1,93E+05 8,21 Benin BN11 (12) 1,12E+05 1,76 Benin BN11 (16) 7,64E+04 1,78 Benin BN11 (19) 2,76E+04 1,87 Benin BN11 (20) 1,95E+05 13,85 Benin BN12 (1) 3,53E+05 16,52 Benin BN12 (8) 4,72E+05 22,15 Benin BN12 (10a) 6,30E+05 22,83 Benin BN12 (10b) 8,13E+05 27,60 Benin BN12 (14) 9,02E+05 31,86 Benin BN12 (16) 4,12E+05 14,88 Benin BN12 (18) 3,76E+04 2,38 Benin BN14 (1) 1,02E+06 38,60 Benin BN14 (4) 5,24E+05 23,70 Benin BN18 (6) 1,14E+06 30,10 Benin BN18 (7) 3,40E+04 2,44 Ivory Coast SA-14 (7) 3,75E+05 15,27 Ivory Coast SA-14 (8) 1,62E+05 7,24 Ivory Coast SA-14 (11) 1,96E+05 9,48 Ivory Coast SA-14 (14) 2,93E+05 12,11 Ivory Coast MK-64 (1) 7,94E+05 28,94 Ivory Coast MK-64 (5) 1,35E+06 30,42 Ivory Coast MK-64 (6) 6,56E+05 15,27 Ivory Coast MK-64 (7) 5,85E+05 16,45 Ivory Coast MK-64 (8) 5,02E+05 18,06 Ivory Coast MK-64 (11) 5,83E+05 16,66 Ivory Coast MK-64 (12) 4,10E+05 12,21 road 1 km N of BN 9 SA-14 4,93300 6,10583 15 granodiorite Batelebre 2 Sassandra massif. Mesocratic. Foliation: N120 to 130°. Dextro-normal shears. 200 10.56113 2.73231 351 Gneiss Guinea 490 granodiorite Guinea 465 granite Benin 298 Gniess Benin 347 Sandstone Guinea GM14-13(1) 1,02E+05 1,55 Guinea GM14-13(2) 9,53E+04 2,74 Benin BN3 (1) 4,17E+04 3,06 Benin BN3 (2) 1,31E+05 5,50 Benin BN5 (3) 8,86E+04 4,81 Benin BN5 (6) 3,78E+05 22,98 Benin BN5 (8) 2,41E+05 7,99 Benin BN9 (16) 6,03E+05 11,72 Benin Benin More or less migmatitic. Mesocratic. Foliation N30°. SA-3 4.72695 6.6293 2 tonalitic gneiss San-Pedro Dextral shears (N80) intruded by pink pegmatites. 199 Guinea 505 granite Guinea 560 biotite gneiss 351 Gniess Benin 345 Gniess Guinea GM14-13(3) 8,52E+04 0,78 Guinea GM14-13(4) 1,77E+05 1,54 Guinea GM14-13(5) 1,42E+05 6,78 Benin BN3 (4) 2,26E+05 14,54 Benin BN3 (5) 1,25E+05 8,31 Benin BN3 (6) 2,06E+05 11,44 Benin BN5 (9) 4,93E+04 2,80 Benin BN5 (10) 3,70E+04 2,49 Benin BN5 (11) 5,14E+04 3,22 BN10 (5) 7,83E+05 18,03 Benin BN10 (6) 6,21E+05 17,62 Benin BN10 (8) 6,80E+05 18,77 Benin Benin Guinea 575 granite 346 Granitoid Guinea GM14-13(6) 1,12E+05 1,01 Benin BN3 (7) 9,41E+04 5,90 Benin BN5 (13) 1,16E+05 5,74 BN10 (11) 3,46E+05 12,89 Benin BN17 (2) 1,06E+05 9,08 Benin BN17 (4) 9,18E+03 3,19 Benin BN17 (6) 2,51E+04 5,40 Benin BN17 (8) 2,48E+04 5,68 Benin BN17 (10) 1,28E+04 3,72 Ivory Coast MK-64 (15) 6,13E+05 1,24 Ivory Coast MK-64 (16) 8,80E+05 28,90 Ivory Coast MK-64 (18) 1,36E+06 34,21 Ivory Coast MK-64 (19) 7,69E+05 24,10 Small outcrop in crops E side of the road 109,3 5,1 13,28 0,17 121,6 4,8 13,38 0,15 138,1 10,0 12,95 0,30 153,7 8,9 13,04 0,21 163,7 12,2 14,14 0,42 170,7 9,0 13,59 0,18 144,8 9,6 13,63 0,21 140,9 4,9 12,52 0,22 142,2 4,9 13,14 0,17 134,7 5,3 12,88 0,17 164,3 4,5 12,72 0,21 143,6 7,3 12,73 0,20 154,8 11,5 12,49 0,21 136,3 4,9 12,44 0,22 202,1 19,1 12,41 0,26 162,7 26,1 12,79 0,28 129,9 4,3 13,28 0,17 122,4 6,4 13,08 0,19 127,0 7,2 13,12 0,19 150,5 5,3 12,89 0,19 139,1 7,2 12,22 0,19 140,3 6,9 13,36 0,17 95,0 3,5 12,92 0,08 125,0 11,0 12,08 0,22 132,0 7,1 12,55 0,14 107,3 6,9 13,06 0,13 106,3 4,5 12,70 0,14 113,4 5,4 12,67 0,12 130,0 11,0 12,32 0,33 386,2 16,0 12,29 0,25 219,0 38,0 11,98 0,29 338,0 13,0 11,56 0,13 380,0 14,0 11,70 0,11 181,5 10,0 12,40 0,16 227,0 15,0 401,0 45,0 109,4 5,8 112,3 25,0 124,6 4,4 113,9 5 150,2 5,7 133,1 3,9 0,0448 0,0084 0,0387 0,3825 0,2433 0,3050 0,0483 0,1059 0,0940 0,0920 0,1048 0,0921 0,0765 0,0112 0,0199 0,0057 0,0112 0,0492 0,0073 0,0464 0,0062 0,0078 0,0048 0,0178 0,0503 0,0592 0,0100 0,0115 0,0170 0,0163 0,1218 0,1615 0,0399 0,0222 0,0399 0,1055 0,0603 0,0830 0,0428 0,0730 0,0755 0,0201 0,0387 0,0170 0,0657 0,1469 0,0882 0,1005 0,0358 0,0312 0,0401 0,0784 0,0435 0,0349 0,1667 0,0580 0,0203 0,0180 0,0234 0,0416 0,0504 0,0264 0,0377 0,0127 0,0412 0,0270 0,0161 0,0226 0,0778 0,0441 0,0145 0,0324 0,0562 0,0632 0,0596 0,0850 0,1308 0,1278 0,1361 0,0935 0,0128 0,0129 0,0136 0,1004 0,1198 0,1606 0,1656 0,2002 0,2311 0,1079 0,0172 0,2800 0,1719 0,0659 0,0231 0,0392 0,0412 0,0270 0,2183 0,0177 0,1107 0,0525 0,0687 0,0878 0,2099 0,2207 0,1107 0,1193 0,1310 0,1208 0,0886 0,0090 0,2096 0,2481 0,1748 183,8 6,22 4,58 1,17 2,70 5,38 2,76 53,12 1,64 33,79 1,07 42,35 10,68 6,70 2,61 14,71 0,85 13,06 11,45 12,77 14,93 14,56 10,93 12,79 9,94 10,62 4,72 1,56 15,50 2,76 11,01 0,78 12,03 1,55 21,79 6,83 18,95 1,02 8,67 6,44 19,73 0,86 10,82 1,09 18,28 0,67 8,57 2,47 13,35 6,99 14,94 8,22 17,85 1,40 19,14 1,59 35,88 2,36 7,26 2,26 7,48 16,91 25,87 22,43 26,67 5,54 15,22 3,08 7,78 5,54 17,95 14,65 19,82 8,37 18,38 11,52 29,55 5,94 27,42 10,14 20,71 10,48 45,57 2,79 12,82 5,37 13,05 2,37 3,55 9,13 33,95 20,40 39,48 12,26 25,32 13,96 13,46 4,97 19,87 4,34 10,32 5,57 7,35 10,89 10,66 6,05 4,43 4,85 1,88 23,14 12,80 8,05 4,43 2,82 0,42 2,51 0,72 3,24 1,77 5,78 3,40 7,01 6,32 3,67 5,54 5,23 31,54 1,77 8,89 5,73 7,28 3,75 4,86 2,24 2,43 3,14 3,38 10,80 14,03 6,13 12,39 2,02 2,88 4,50 2,67 7,81 7,32 8,78 0,58 8,27 1,15 11,80 1,00 18,17 0,34 17,74 0,26 18,91 0,57 12,99 0,22 1,77 2,26 1,79 5,02 1,88 2,82 13,95 22,09 16,64 1,28 22,31 1,54 23,00 2,73 27,80 2,88 32,10 4,01 14,99 1,88 2,39 -0,14 38,88 2,82 23,87 2,29 9,15 0,63 3,21 0,48 5,44 0,43 5,72 0,69 3,75 1,30 30,32 11,42 2,46 2,56 15,38 51,84 7,29 25,26 9,54 28,70 12,20 41,56 29,14 30,43 30,65 42,39 15,38 47,44 16,57 17,07 18,19 21,99 16,78 18,71 12,30 12,89 1,25 36,04 29,11 33,54 34,46 41,11 24,28 27,35 7,2 12,17 0,21 11,84 0,54 12,87 0,15 10,31 0,70 12,60 0,139 12,58 0,13 12,62 0,128 13,03 0,11 12,63 0,11 7,30 1,80 6,03 53,51 34,04 44,86 7,32 14,91 15,74 16,28 17,12 15,13 11,73 13,80 5,20 12,95 5,35 13,91 3,61 12,20 6,67 14,13 11,28 7,87 3,05 10,94 11,07 8,91 3,41 10,21 5,38 2,68 11,20 5,61 15,62 10,50 12,42 5,89 10,03 4,07 4,02 22,99 28,70 9,11 4,91 31,01 9,76 19,31 26,16 12,69 30,70 18,47 28,17 12,39 33,56 15,01 233,87 21,19 6,61 5,81 22,24 8,44 13,17 3,20 44,20 17,11 43,78 29,68 34,68 18,21 17,12 5,39 9,64 4,50 6,76 7,30 13,39 7,09 5,29 26,15 9,09 2,92 2,68 3,66 6,58 1,72 8,49 4,97 12,64 3,86 7,44 4,90 2,81 3,94 14,10 9,04 2,69 5,13 9,53 8,91 8,55 12,04 18,25 17,80 19,04 13,04 2,30 2,97 2,55 19,14 16,94 22,67 23,64 28,48 33,04 15,43 2,36 39,55 24,40 9,30 3,32 5,54 5,88 4,05 33,01 3,06 27,56 13,23 16,29 21,97 36,30 40,61 26,53 20,58 23,36 21,18 15,33 9,71 36,99 44,12 30,71 49,5 48,5 42 69 98 75,5 60 81,5 65,5 73 64 44 53,5 57 54,5 74 43 55 100,5 57 100 38 67,5 46,5 71 68,5 53,5 54 71,5 72,5 51 47,5 42,5 66,5 71,5 64 72 72 62 78 85,5 140 110 92,5 74,5 58,5 54,5 62 111,5 78 50 61,5 93 153,5 45,5 99,5 121 134 137,5 126 52,5 57,5 97 39 36,5 65,5 45,5 46,5 33,5 41,5 43 46,5 54 66 65,5 51,5 121 108 96,5 92,5 128 59 89,5 57,5 62,5 77,5 69,5 73 78,5 92 64,5 140 75 64,5 93 71 45 49 26 47,5 57,5 60 77,5 56 55,5 49,5 119,5 92,5 81,5 75 96 71 50 89,5 64,5 1,73 1,46 2,35 2,09 1,50 1,79 1,65 2,17 1,65 1,68 2,09 1,97 2,12 2,18 2,59 1,46 1,66 1,93 1,88 1,89 1,91 1,74 1,21 1,55 1,44 1,38 1,45 1,26 1,42 1,36 1,36 1,60 1,50 1,63 1,58 1,53 1,46 1,85 1,39 1,31 1,56 1,25 1,17 47,52 50,06 48,05 80,97 98,33 90,48 72,47 92,46 69,71 69,53 74,96 54,10 65,26 71,81 58,96 73,83 53,36 56,42 98,60 59,98 103,42 45,48 73,07 54,41 69,07 75,83 58,84 69,18 75,23 75,27 56,70 59,52 52,62 80,99 73,54 77,55 77,98 78,32 60,79 78,66 77,83 158,78 111,14 91,48 86,86 66,75 60,78 73,97 114,35 83,07 58,70 71,04 115,61 160,19 60,85 113,34 128,96 158,52 153,78 135,36 58,83 59,51 97,00 44,24 41,65 70,81 50,04 51,78 42,10 46,73 48,19 51,27 57,61 78,32 68,53 64,88 121,00 122,86 112,23 110,70 149,70 67,10 103,40 71,42 73,92 90,62 58,25 72,32 91,68 106,65 76,12 143,78 75,49 76,39 99,21 82,11 51,34 56,59 33,77 52,40 69,75 70,36 84,47 63,55 68,32 60,14 138,87 117,76 90,47 93,19 119,49 86,28 63,39 104,91 82,84 100 R. W. Guinea WNW of Zouta YOR-2 7,47733 7,39067 308 granodriorite Yorogoué village 4.6 km Same as YOR-1 41 Appendix 6. Country YOR-1 7,47733 7,39067 308 granodriorite Yorogoué village 4.6 km WNW of Zouta Domple massif. Deformation up to weak augen gneiss texture. Foliation: N40 41 BN 5 9.19113 2.55006 374 Granitoid Artisanal quarry E side of road S of Parakou Porphyritic granite showing transitional (fuzzy) facies with diatexitic gneisses suggesting genetic relationships. Parakou granite. Locally Elevation_ m Lithology Guinea 475 granite Guinea 400 amphibolite gneiss Guinea 669 granodiorite Benin 338 Migmatite Benin 397 Granitiod Benin 247 Sandstone Guinea GM14-01 (1) 1,76E+05 12,98 Guinea GM14-13(7) 2,03E+05 7,99 Guinea GM14-13(8) 2,02E+05 10,09 Guinea GM14-13(9) 7,13E+04 1,52 Guinea GM14-13(10) 2,16E+05 1,99 GM14-13(11) 8,90E+04 4,87 Benin BN3 (8) 9,74E+04 5,20 Benin BN3 (9) 2,30E+05 10,59 Benin BN3 (10) 4,23E+04 3,55 Benin BN3 (11) 3,93E+05 12,60 Benin BN3 (12) 6,88E+04 8,66 Benin BN7 (1) 7,65E+04 3,48 Benin BN7 (2) 8,28E+04 3,36 Benin BN7 (3) 2,50E+05 7,72 Benin BN7 (4) 2,94E+05 8,78 Benin BN11 (1) 1,99E+04 1,27 Benin BN11 (2) Benin BN11 (5) 3,64E+04 1,25 Benin BN11 (11) 5,48E+04 2,57 Benin BN17 (14) 1,17E+05 9,86 Benin BN18 (1) 1,89E+05 15,44 Benin BN18 (2) 3,37E+05 6,00 a AFT_Age_M AFT_Age_E rr A_MTL_μ m A_MTL_E rr 129,9 5,8 13,12 0,18 158,4 4,7 13,02 0,16 150,2 5,0 13,41 0,17 202,5 8,0 167,9 7,3 217,0 33,0 0,0942 0,0580 0,0732 0,0110 0,0144 0,0354 0,0377 0,0768 0,0257 0,0914 0,0628 0,0253 0,0244 0,0560 0,0636 0,0092 0,0091 0,0187 0,0715 0,1120 0,0435 ppm 232Th ppm 13,08 12,69 8,05 18,97 10,17 28,56 1,53 7,68 2,00 25,43 4,91 11,89 5,24 12,31 10,66 49,66 3,57 5,95 12,69 45,07 8,72 24,91 3,51 5,37 3,39 2,38 7,78 6,14 8,84 8,46 1,28 1,40 1,26 8,05 2,59 7,59 9,93 0,79 15,55 3,54 6,04 10,26 12,75 0,11 12,26 0,15 11,42 0,35 147Sm ppm eU ppm 16,06 15,79 12,51 20,86 16,88 8,08 3,34 7,98 12,13 7,70 16,69 8,13 59,28 22,33 22,76 4,97 20,74 23,29 14,57 0,82 4,77 1,36 3,95 9,22 10,83 1,61 3,15 4,37 10,11 16,38 8,45 incipient or pervasive dextral CS fabrics. S: N20, 90 ; C: N50, 90. d Radius μm 40,5 54 46 109 65 70,5 78 65,5 61 61,5 36,5 55,5 72 59,5 34 101 108 120,5 56 27 80 A_MTL_St s 1,83 1,64 1,66 1,38 1,66 2,01 R* μm 47,04 61,65 53,52 115,07 72,35 81,10 78,98 75,39 67,75 64,91 45,48 57,93 64,07 67,35 40,09 107,40 118,04 137,23 66,83 34,07 82,65 Num_Length Dpa r Person Brown 100 R. W. Brown 60 R. W. Brown 100 R. W. Brown 13 R. W. Brown 100 R. W. Brown 63 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 27 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 100 R. W. Brown 262 1,89 M. Wildman 49 1,78 M.Wildman 100 1,78 M.Wildman 106 1,75 M.Wildman 104 1,66 M.Wildman 105 1,72 M.Wildman 19 1,87 M.Wildman 134 2,04 M. Wildman 22 2,00 M. Wildman 151 1,86 M. Wildman 249 2,02 M. Wildman 102 1,73 M. Wildman 151 1,90 M. Wildman 120 1,69 M. Wildman 33 1,81 M. Wildman 55 1,78 M. Wildman 8 1,88 M. Wildman 98 1,69 M. Wildman 8 1,76 M. Wildman 102 1,68 M. Wildman 100 1,87 M. Wildman 149 1,88 M. Wildman 103 1,84 M. Wildman Terminatio ns 1 1 2 2 Mean 1 2 1 1 2 2 Mean 1 1 1 2 2 Mean 2 1 1 1 1 0 1 1 1 1 1 1 1 1 2 1 1 Mean 2 2 2 Mean 1 1 1 2 2 Mean 2 0 2 1 1 0 1 1 1 1 2 1 1 1 0 1 1 1 1 2 1 1 Mean 2 2 2 Mean 1 2 2 2 2 2 2 Mean 1 1 2 2 1 2 1 1 1 2 2 2 2 2 2 1 2 Mean 2 1 2 Mean 1 2 2 2 Mean 1 2 2 2 2 2 2 2 Mean 2 2 2 2 2 2 2 Mean 1 1 Mean 2 2 2 2 2 2 Mean 2 2 2 2 Mean 2 2 2 2 Mean 2 2 2 2 2 2 2 2 2 2 2 Mean 116 1,85 M. Age_M a 90,11 120,58 289,04 194,83 173,64 135,48 421,71 84,27 108,30 645,78 121,18 252,79 107,55 108,36 104,87 52,83 55,14 85,75 157,38 142,67 186,39 212,91 101,82 291,70 131,11 97,23 170,92 220,73 93,53 40,77 247,92 243,75 219,87 145,20 165,18 168,77 156,83 211,41 102,76 157,00 80,78 103,53 127,58 107,90 79,82 99,92 69,65 107,47 95,94 79,73 90,13 61,19 96,53 82,51 67,22 137,04 38,80 118,93 106,31 117,29 104,84 109,20 150,91 101,26 102,77 92,47 96,49 93,97 96,39 86,35 105,27 106,85 99,49 136,91 118,30 215,02 138,26 113,20 115,21 144,29 140,17 130,64 170,07 220,42 220,43 524,85 153,53 153,18 356,28 141,61 175,76 117,90 147,69 145,45 127,17 140,86 200,18 211,30 196,31 232,65 184,00 399,74 272,13 344,04 281,40 287,99 215,36 282,20 101,31 225,15 94,78 102,72 391,22 208,89 89,04 83,49 162,07 169,89 169,94 216,31 231,47 221,61 216,52 130,43 193,74 209,90 174,86 192,38 93,75 22,83 37,45 34,79 26,00 95,35 51,69 94,62 320,99 279,23 90,90 196,43 111,49 100,54 98,73 109,06 104,95 178,19 268,34 201,36 230,60 175,13 223,60 217,28 509,04 193,59 249,65 203,62 240,95 Wildman error 9,01 12,06 28,90 19,48 17,36 13,55 42,17 8,43 10,83 64,58 12,12 25,28 10,75 10,84 10,49 5,28 5,51 8,57 15,74 14,27 18,64 21,29 10,18 29,17 13,11 9,72 17,09 22,07 9,35 4,08 24,79 24,37 21,99 14,52 16,52 16,88 15,68 21,14 10,28 15,70 8,08 10,35 12,76 10,79 7,98 9,99 6,96 10,75 9,59 7,97 9,01 6,12 9,65 8,25 6,72 13,70 3,88 11,89 10,63 11,73 10,48 10,92 15,09 10,13 10,28 9,25 9,65 9,40 9,64 8,63 10,53 10,69 9,95 3,41 11,83 21,50 13,83 11,32 11,52 14,43 14,02 13,06 17,01 22,04 22,04 52,48 15,35 15,32 35,63 14,16 17,58 11,79 14,77 14,55 12,72 14,09 20,02 21,13 19,63 23,27 79,17 39,97 27,21 348,6 8 28,14 28,80 21,54 28,22 10,13 22,51 9,48 10,27 39,12 20,89 8,90 8,35 16,21 16,99 16,99 21,63 23,15 22,16 21,65 13,04 19,37 20,99 17,49 19,24 9,38 2,28 3,74 3,48 2,60 9,54 5,17 9,46 32,10 27,92 9,09 19,64 11,15 10,05 9,87 10,91 10,50 17,82 26,83 20,14 23,06 17,51 22,36 21,73 50,90 19,36 24,97 20,36 24,09

rouges. La côte des plaques en déplacement est indiquée en orange. Les punaises violettes marquent des blocs qui ne bougent pas. LMA : 133 Ma, M7 : 127,5 Ma, M4 : 125,7 Ma, M2 :123,5 Ma, M0 : 121 Ma, C34: 84 Ma. La datation de M7, M4 et M2 sont d'après[START_REF] Gaina | The African Plate: A history of oceanic crust accretion and subduction since the Jurassic[END_REF]. Voir Table2 dansl'Annexe pour les pôles Eulériens utilisés. Modèle de l'ouverture de l'Atlantique Sud (Figure 2-20, Moulin et al., 2010): Hautérivien-Barrémien (LMA-M4) (133 Ma -125,7 Ma) : L'ouverture de l'Atlantique Sud commence par le segment austral à la suite d'un événement magmatique de Parana-Etendeka en Angola et Namibie. En même temps, des blocs Sud de l'Amérique du Sud se déplacent à l'Ouest. Aptien Inférieur (M4-M0) (125.7-121 Ma) : Le segment austral continue à s'ouvrir du Sud au Nord. Des blocs Sud de l'Amérique du Sud continuent à se déplacer à l'Ouest. Le bloc austral Africain (voir 1 se met à se déplacer vers le NE et le bloc Nubien vers le Nord durant principalement 125.7-123 Ma (M4-M2). Aptien Supérieur(M0)-Albien Inférieur (121-112 Ma) : Le segment central se met à s'ouvrir par un saut de ride océanique vers l'Est à la limite Aptien-Albien en même temps que la déposition du sel se termine. En conclusion, l'Atlantique Sud s'est ouverte du Sud au Nord du segment austral au segment central à partir de Hauterivien (133 Ma). Les déformations intra-plaques étaient impliquées sur le continent Africain et Sud-Américain au cours de l'ouverture. La connexion entre l'Atlantique Sud et Centrale s'est faite ensuite par l'ouverture de l'Atlantique Equatorial.2.4.3. Ouverture de l'Atlantique EquatorialL'Atlantique Equatorial est limitée au Nord par la zone de fracture de Marathon, au Sud par la zone de fracture d'Ascension. Elle forme un étroit passage orienté NW-SE avec une dorsale océanique fortement segmentée. L'étude de l'évolution tectono-sédimentaire de l'Atlantique Equatorial et ses marges passives constituent une partie majeure de la thèse.

[START_REF] Valsardieu | Etude géologique et paléogéographique du Bassin de Tim Mersoï, région d'Agadès[END_REF] Genik, 1993). The rest of the continental domain is potentially subjected to erosion. The Central Atlantic Magmatic Province (CAMP, dated at 235-185 Ma with a peak activity at 200 Ma,Jourdan et al., 2009, Appendix 1), affects most of the exposed domain in the form of extensive lava flows, sills and dykes. Large sills may still be buried within the Taoudeni basin, as well as onshore South American basins. Given the very limited number of lava flow occurrences compared to sills and dikes, significant (several kilometers) post-CAMP surface erosion must have taken place. Outside the CAMP, ring complexes emplaced in the Nigeria Shield (Younger Granites, dated at 213-141 Ma), and near the Hoggar Shield (dated at 215-166 Ma). Most of the continental domains outside the Central Atlantic rift system may have been subject to massive erosion, forming a "CAMP superswell" fringed by a drainage network feeding a proto-Saharan basin.

Figure 5-3: Seven extrapolated cross-sections along the Sierra Leone-Liberia margin from North to South (SL-LB1 to SL-LB7). Location is indicated in Figure 5-1.

Remerciements

List of Tables

CHAPTER 3 : PALEOGEOGRAPHIC AND STRUCTURAL RECONSTRUCTION Abstract

The tectonic, magmatic, sedimentary and erosional histories of Northwestern Africa and its adjoining continental margins are investigated in the light of nine successive Meso-Cenozoic paleogeological maps. Mapping is based on a compilation of original data on the stratigraphy, depositional environments, structures and magmatic occurrences, as well as extensive integration of industrial seismic and borehole data. Maps integrate original minimal extent of sedimentary deposits beyond their present-day erosional limits and published thermochronological data are used to further constrain areas under burial or erosion.

Rifting propagated eastward from the Central Atlantic between the Valanginian (ca. 140

Ma) and the Aptian (ca. 112 Ma) as an en-échelon transform-rift system connected to an inland rift network, defining a 6-microplate syn-rift pattern for the African continental domain. The preopening fit between Africa and South America is refined. Persistent / renewed eroding upwarps along the continental margin are documented. They fed both the margin basins and a very large, persistent intracratonic basin, which acted as a transient sediment reservoir because the products of its erosion were transferred both to the Tethys (to the north) and to the Equatorial Atlantic Ocean

PAPER 2 -Structural variability of the African Equatorial

Atlantic margin and post-rift stratigraphic implication

Manuscript in preparation

Abstract

We investigated the structural variability and the early post-rift stratigraphic architecture along the African Equatorial Atlantic margin. The segmentation of the margin results from the obliquity of each segment with respect to the orientation of transform faults bounding the main depot-centres (Sierra Leone-Liberia, Ivory-Coast, Ghana-Togo-Benin). This produced variable widths of the necking zone of the crust and the continent-ocean transition from one segment to the other. We show that this has a significant impact on the early post-rift stratigraphic architecture of the margin segments. In particular, the proximal parts of this sedimentary wedge are only preserved along divergent segments of the margin and not along transform segments. We interpret this differential preservation as the result of a greater flexural uplift, during the immediate post-rift, in the proximal parts of the transform segments, preventing the preservation. We also documented, in the proximal part of the divergent margins, a regional uplift event (x100m) during the Santonian (ca. 84 Ma) that could be related to either mantle driven dynamics or regional changes in lateral stress regime.

Résumé

Nous avons analysé la variabilité structurale et l'architecture stratigraphique de l'immédiat post-rift le long de la marge Atlantique Equatoriale africaine. La segmentation de la marge résulte de l'obliquité de chaque segment de la marge par rapport à l'orientation des failles transformantes délimitant des dépôt-centres principaux (Sierra Leone-Liberia, Côte d'Ivoire, Ghana-Togo-Benin).

Ceci se traduit par des variations, d'un segment à l'autre, de la largeur de la zone d'amincissement de la croûte (necking zone) et de la transition océan-continent. Nous montrons que cette segmentation a un très fort impact sur l'architecture stratigraphique de l'immédiat post-rift des segments. En particulier, les parties proximales du prisme sédimentaire ne sont préservées que dans des segments divergents et pas sur des segments transformants. Nous interprétons cette THE AFRICAN EQUATORIAL ATLANTIC MARGIN 142 where V(z) is the velocity at depth z, V0 is the initial velocity, k is the velocity gradient (s -1 ). V0 and k were determined and calibrated to well log measurements. k is fixed here to be 0.5 s -1 . V0 of 1500 m/s is used for the Cenozoic layer, 2350 m/s for the Upper Cretaceous layer.

In the Ivory Coast basin, we defined a polynomial law (2) from velocity measurements in 12 wells:

where x is the two-way time (s), and y is the depth (m).

In the Sierra Leone-Liberia basin, we defined another polynomial law (3) based on 8 wells:

We checked depth conversion by measuring the deviation of depth converted horizons at wells and ensured that the uncertainty remains under 15%.

Cross-sections Extrapolation

We first constructed cross-sections from depth converted horizons. Since exploration seismic profiles are usually limited to the proximal part of the margin, onshore coastal basins (e.g., Togo-Benin embayment) and distal parts of the sedimentary system are not covered by those crosssections. We first extrapolated cross-sections landward to bridge the gap between the seismic profiles and landward sediment onlaps in coastal basins using mostly the geological map. To incorporate sediments deposited in the distal part of the system into the abyssal plain, which constitute a non-negligible quantity of terrigenous sediments transported by gravity processes, we also extrapolated cross-sections towards the present-day oceanic ridge to the edge of the basin. We used published seismic profiles [START_REF] Emery | Continental margin off western Africa; Angola to Sierra Leone[END_REF], bathymetric and basement maps (ETOPO5; [START_REF] Laske | A Global Digital Map of Sediment Thickness: EOS Trans[END_REF], and the age of oceanic crusts to avoid older sediments to be extended upon younger oceanic crust. We constructed 7 extrapolated cross-sections in the Sierra Leone- The problem encountered with this method is that the spontaneous tracks are produced by 238 U atoms located on both sides of the etched surface, whereas the induced tracks in the external detector result from only 235 U atoms located within the specimen. So a correction is suggested by some authors by increasing the measured U concentration by two or reduced the spontaneous track density [START_REF] Faure | Principles of isotope geology[END_REF].

Results

The results show the denudation-induced uplift of the continent and the sediment loadinginduced subsidence (Figure 7 -Dominated by bauxite plateau @ 570 m: has undergone 270 of denudation since 45 Ma.

Appendix 3. Localization and features of samples collected in Guinea

-Middle glacis province: Negligible denudation since 6 Ma.

APPENDIX

-Has been buried under later Ordovician and Silurian sediments (probably eroded here).

GM4 10,01673 -12,82185 324 Sandstone -Ordovician sandstone deposited (therefore exposed) in shore environment between ca. 490 and 445 Ma (duration of the Ordovician).

-Middle glacis surface: no denudation since 6 Ma. Bauxitic cuesta up to 1100 m: More than 700 m of denudation since 45 Ma.

-Has been buried under later Ordovician and Silurian sediments (probably eroded here).

GM5 10,02741 -12,67767 255 Dolerite -CAMP dolerite sill (ca. 203 Ma?).

-Middle glacis surface: no denudation since 6 Ma.

GM6 10,1125 -12,55918 125 Sandstone -Neoproterozoic sandstones deposited @1350 -1000 Ma(?) (Madinakouta formation). Series containing limestones.

-Dominated by bauxitic mesa @ 870 m: 700 m of denudation since 45 Ma.

-Had been buried under Ordovician and Silurian series.

-Numerous large CAMP sills in the environment of the sample.

GM7 10,71441 -12,24887 1247 Sandstone -Ordovician sandstone deposited (therefore exposed) in shore environment between ca. 490 and 445 Ma (duration of the Ordovician).

-Has been buried under later Ordovician and Silurian sediments (probably eroded here).

-Numerous large CAMP sills in the environment of the sample.

-Hilly bauxitic relief: no significant denudation since 45 Ma.

GM8 10,7017 12,25725 1228 Dolerite -CAMP dolerite (ca. 203 Ma?).

-Hilly bauxitic relief: no significant denudation since 45 Ma.

GM9 10,61369 -12,19874 980 Dolerite -CAMP dolerite (ca. 203 Ma?). Large sill with equant texture and large crystals.

-Hilly bauxitic relief: no significant denudation since 45 Ma.

GM10 10,6038 -11,85709 840 Dolerite -CAMP dolerite (ca. 203 Ma?). Fresh corestone in weathering profile.

dominated by bauxitic plateau @ 920 m: 100 m of denudation since 45 Ma.

GM11 10,6364 -11,81488 784 Granitoid -dominated by bauxitic plateau @ 910 m: 100 m of denudation since 45 Ma.

thick CAMP sill structurally under the sample.

GM12 10,73259 -11,57986 679 Granitoid -dominated by bauxitic plateaux @ 920 m: 250 m of denudation since 45 Ma.

GM13 10,73559 -11,29056 656 Granitoid -dominated by bauxitic plateaux @ 980 m: 300 m of denudation since 45 Ma.

middle glacis surface: no denudation since 6 Ma.

GM14 10,82268 -10,99629 438 Granitoid -dominated by bauxitic plateaux @ 1100 m: 550 m of denudation since 45 Ma.

middle glacis surface: no denudation since 6 Ma.

structurally below a major CAMP sill.

GM15 10,91783 -10,74739 496 Granitoid -dominated by bauxitic plateaux @ 1000 m: 500 m of denudation since 45 Ma.

middle glacis surface: no denudation since 6 Ma.

GM16 10,73857 -10,08871 415 Granitoid -middle glacis surface: no denudation since 6 Ma.

GM17 12,347 -8,40856 430 Sandstone -Basal term of the Neoproterozoic Taoudeni basin forming the regional escarpment.

-Bauxites top the cuesta @ 700 m: 250 m of denudation since 45 Ma.

-Must have been buried under later Neoproterozoic sediments (at least).

GM18 12,66357 -7,98985 438 Sandstone -Neoproterozoic sandstones forming the upper part of the Taoudeni basin escarpment.

-75 under the bauxite: limited erosion since 45 Ma.

-Must have been buried under later Neoproterozoic sediments (at least).

GM19 12,66337 -7,98911 408 Sandstone -Neoproterozoic sandstones forming the lower part of the Taoudeni basin escarpment (same section as GM 18).

-90 under the bauxite: limited erosion since 45 Ma.

-Must have been buried under later Neoproterozoic sediments (at least).

GM20 Was therefore exposed and near sea level sometime between ca. 490 and 420 Ma and could have been buried consequently.

-Collected from an extensive, slightly dissected middle glacis relict landscape. Has therefore undergone negligible denudation since 6 Ma.

-Sample lying along the western margin of the Kandi basin, exposing a thin (<100 m) Cretaceous continental formation (chronostratigraphic uncertainties on the tree remains does not allow asserting an age within the Cretaceous). The sample was therefore exposed at the surface before filling of the Kandi basin sometime between ca. 140 and 70 Ma.

BN 9 10.56113 2.73231 351 Gneiss -Collected from an extensive, slightly dissected middle glacis relict landscape. Has therefore undergone negligible denudation since 6 Ma.

-Sample is located at the western margin of the Kandi basin, exposing a very thin (<100 m) Cretaceous continental formation (tree remains suggest a Lower Cretaceous age). The sample was therefore exposed at the surface sometime between ca. 140 and 100 Ma.

BN 10 10.37225 2.72320 345 Gneiss -Collected from an extensive, slightly dissected middle glacis relict landscape. Has therefore undergone negligible denudation since 6 Ma. BN 11 9.77403