Ponte Jean-Pierre

Cécile Robin

François Guillocheau

Speranta Popescu

Jean- Pierre Suc

Massimo Dall'asta

Mihaela C Melinte-Dobrinescu

Miroslav Bubik

Gérard Dupont

Jéremie Gaillot

Jean-Pierre Ponte

Jean-Pierre Suc

Beira High

C C Sdr

Tortonian Messinian

Zanclean Piacenzian

Gelasian Calabrian

Ionian Tarant

Miocene

The Zambezi delta (Mozambique channel, East Africa): High resolution dating combining bio-orbital and seismic stratigraphy to determine climate (palaeoprecipitation) and tectonic controls on a passive margin

Introduction

The Zambezi Delta (Fig. 1) currently drains the South African Plateau (NE portion of the Kalahari Basin; (Thomas and Shaw,1988;[START_REF] Moore | Drainage evolution in south-central Africa since the breakup of Gondwana[END_REF] and the southern portion of the East African Rift (Fig. 1) and has the third largest catchment (1 320 000 km 2 ) in Africa, after the Nile and the Congo. Its current sediment load is not well known, but is estimated to range from 20.10 6 to 48.10 6 t/yr [START_REF] Milliman | Geomorphic/tectonic control of sediment discharge to the ocean: the importance of small mountainous rivers[END_REF]. Across all geological eras, the Zambezi Delta is the longest operating delta in Africa starting in the Early Cretaceous with more than 12 km of sediments deposited with 5 km during the Cenozoic (Salman and Abdula, 1995) and with no gravitary tectonics due to the absence of a major decollement level.

The size and location of the Zambezi River catchment has changed throughout the geological eras, and in the most recent times it also captures the upstream portion of the Limpopo River [START_REF] Nugent | The Zambezi River: tectonism, climatic change and drainage evolution[END_REF][START_REF] Moore | The Zambezi River[END_REF]. These changes resulted from deformation of the South African Plateau when it was uplifted during the Late Cretaceous and Oligocene [START_REF] De Wit | The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space[END_REF][START_REF] Braun | Rapid erosion of the Southern African Plateau as it climbs over a mantle superswell[END_REF] and deformation of the East African Rift System (EARS) [START_REF] Chorowicz | The east African rift system[END_REF] with formation of the Malawi Rift, which is assumed to have occurred in the late Miocene (Ebinger, 1989;Ebinger et al., 1993).

The topographic growth of EARS domes and rift shoulders had a first order impact on climate change in East Africa (Sepulchre et al., 2006), influencing atmospheric circulation, moisture transport and spatial patterns of precipitation, and therefore sedimentary flux of the deltaic systems [START_REF] Milliman | Geomorphic/tectonic control of sediment discharge to the ocean: the importance of small mountainous rivers[END_REF]. Several studies have focused on changes in palaeoclimate that occurred in the EARS (e.g. Jacobs and Herendeen, 2004;Trauth et al., 2005;

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2 Sepulchre et al., 2006;Vincens et al., 2006;[START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF]Feakins et al., 2013;[START_REF] Rasmussen | Middle -late Miocene palaeoenvironments, palynological data and a fossil fish Lagerstatte from the Central Kenya Rift (East Africa)[END_REF], but only the study of [START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF] summarised the continuous climate record since the late Miocene.

The Zambezi Delta is a unique archive (its long duration and absence of gravitary tectonics preserve the geometry of depositional sequences) for studying the influences of deformation and climate controls on the delta and its upstream catchment. Doing so requires high-resolution (around 1 Ma) age calibration of deltaic infilling.

Our study had two objectives: (1) construct an age model of the Zambezi Cenozoic delta using a combination of biostratigraphy, orbital stratigraphy and sequence stratigraphy, and (2) determine the precipitation record of the upstream catchment of the Zambezi Delta from the Oligocene to present day. We developed a new method using high-resolution cycles defined on seismic lines (seismic stratigraphy) to design an age model that combines biostratigraphy and orbital stratigraphy (which is the new feature).

The study is based on subsurface data: (1) seismic reflection lines for seismic stratigraphic analysis and (2) wells with well logs for seismic calibrations using lithology, age and drill cuttings to explore the micropaleontology (calcareous nannofossils, planktonic foraminifera) and palynology (pollen grains and spores).

Methodology

Data

The study is based on a set of 2D seismic reflection data shot in 1970s and 1980s and four petroleum wells (X, X1 to X3, Fig. 1) drilled in the 1970s located on seismic profiles with welllogs and cuttings, provided by TOTAL.

Seismic stratigraphy

Since the 1970s, several successive approaches to seismic stratigraphy have been developed which are more complementary than in opposition.

Researchers at Exxon developed the first approach [START_REF] Brown | Seismic-stratigraphic interpretation of depositional systems: Examples from Brazilian Rift and pull-apart basins[END_REF][START_REF] Mitchum | Seismic stratigraphy and global changes of sea level: Part 2. The depositional sequence as a basic unit for stratigraphic analysis[END_REF], which is based on subdividing depositional sequences into system tracts to identify relative sea level variations in the sedimentary record and now known as the balance between the accommodation space (Jervey, 1998) and the sediment flux (see Neal andAbreu, 2009 andAbreu et al., 2011 for a review). System tracts, corresponding to stages of the relative sea level variations (Fig. 2), are bounded by three stratigraphic surfaces with truncations: (1) the unconformity (Un or sequence boundary SB) below onlaps, (2) the Maximum Flooding Surface (MFS) below downlaps, and (3) the Maximum Regressive Surface (MRS, formerly Transgressive Surface or Flooding Surface) above toplaps (Fig. 2). Some criticism was launched against this revolutionary model in the early 1980s. For example, no shoreline deposits were preserved when the relative sea level fell. [START_REF] Plint | Sharp-base shoreface sequences and" offshore bars" in the Cardium Formation of Alberta: their relationship to relative changes in sea-level[END_REF] and [START_REF] Hunt | Stranded parasequences and the forced regressive wedge systems tract: deposition during base-level fall[END_REF] suggested defining a new system tract, the Forced Regressive Wedge System Tract (FRWST), which corresponds to sediments deposited during the fall in relative sea level.

Researchers at Norsk Hydro [START_REF] Helland-Hansen | Conceptual basis and variability in sequence stratigraphy: a different perspective[END_REF][START_REF] Helland-Hansen | Shoreline trajectories and sequences: description of variable depositional-dip scenarios[END_REF][START_REF] Helland-Hansen | Trajectory analysis: concepts and applications[END_REF] developed a technique based on the offlap break (shoreline or shelf-edge break) trajectory over time by defining stratal patterns: forced (descending) regressive, normal (ascending) regressive and transgressive (see Fig. 2 for its relations with relative sea level variations and Exxon's approach). In 2009, Catuneanu and 28 coauthors synthetized and standardised the approaches used to define the relation between the system tract, stratigraphic surfaces and clinoform geometry.

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4

A depositional sequence is here defined as follows:

• the sequence boundary that corresponds to the first correlative conformity (CC, [START_REF] Catuneanu | Towards the standardization of sequence stratigraphy[END_REF] and the onset in continental domain to the subaerial unconformity, an erosion surface overlain by onlapping strata;

• the forced regressive (FR) deposits [START_REF] Catuneanu | Towards the standardization of sequence stratigraphy[END_REF] (equivalent of the forced regressive wedge system tract of [START_REF] Hunt | Stranded parasequences and the forced regressive wedge systems tract: deposition during base-level fall[END_REF] or the falling-stage system tract -FSST -of [START_REF] Plint | The falling stage systems tract: recognition and im-portance in sequence stratigraphic analysis[END_REF], which are not in the Exxon's model, correspond to descending regressive shorelines (i.e forced progradation) passing toward the deep-sea plain to the basin floor fan;

• the lowstand normal regressive (LNR) deposits [START_REF] Catuneanu | Towards the standardization of sequence stratigraphy[END_REF] which correspond to the lowstand system tract (LST) of [START_REF] Posamentier | Eustatic controls on clastic deposition II -sequence and systems tract models[END_REF] or ascending regressive shorelines (i.e progradation-aggradation) of Helland-Hansen (e.g. Helland- [START_REF] Helland-Hansen | Trajectory analysis: concepts and applications[END_REF];

• the maximum regressive surface (MRS), which corresponds to the former transgressive or flooding surface [START_REF] Posamentier | Eustatic controls on clastic deposition II -sequence and systems tract models[END_REF] above the toplapping strata;

• the transgressive deposits (T; [START_REF] Catuneanu | Towards the standardization of sequence stratigraphy[END_REF] which correspond to the transgressive system tract (TST) of [START_REF] Posamentier | Eustatic controls on clastic deposition II -sequence and systems tract models[END_REF] or transgressive shorelines (i.e retrogradation) of Helland-Hansen (e.g. Helland-Hansen and Hampson, 2009);

• the maximum flooding surface (MFS) which lies below downlapping strata;

• the highstand normal regressive (HNR) deposits [START_REF] Catuneanu | Towards the standardization of sequence stratigraphy[END_REF] which correspond to the highstand system tract (HST) of [START_REF] Posamentier | Eustatic controls on clastic deposition II -sequence and systems tract models[END_REF] or ascending regressive M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 5 shorelines (i.e progradation-aggradation) of Helland-Hansen (e.g. Helland-Hansen and Hampson,2009).

Based on their cause -climate or lithosphere deformation, relative sea level variations occurred over different durations in past geological periods [START_REF] Graciansky | Mesozoic and Cenozoic sequence stratigraphy of European Basins[END_REF]. As a consequence, the stratigraphic record is a stacking of different orders of nested sequences.

Determining the hierarchy of depositional sequences (between two sequence boundaries) or stratigraphic cycles (between two MFS) on a 2D section is difficult due to changes in the sedimentation rate over time. [START_REF] Mitchum | Seismic stratigraphy and global changes of sea level: Part 2. The depositional sequence as a basic unit for stratigraphic analysis[END_REF][START_REF] Bartek | Effect of Cenozoic ice-sheet fluctuations in Antarctica on the stratigraphic signature of the Neogene[END_REF] defined orders of sequences based on their duration (first order: around 100 -200 Myrs, second order: several 10 Myrs, third order: several 1 Myrs, fourth order: several 100 kys). This indicates that dating is required to determine a suitable hierarchy of sequences and cycles.

Sediment dating: age model

As mentioned in the introduction, the high-resolution dating (expected around several 0.1 Ma) of the Neogene sediments is based on a combination of biostratigraphy, orbital stratigraphy and sequence stratigraphy. The temporal resolution of planktonic foraminifer and calcareous nannofossil biozones [START_REF] Gradstein | The geologic time scale 2012[END_REF] ranges from several 100 kys to several Myrs for the Neogene, which is not high enough for our study.

Increasing the temporal resolution is here based on two approaches (see discussions below). The first is biostratigraphic, examining strata boundaries using cuttings to provide a possible age range for formations. The second is orbital stratigraphic, based on identifying depositional sequences that may have been influenced by climate-induced sea level variations related to variations in the Earth orbit.

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The studied samples are ditch raw cuttings collecting sediments of a few centimetres in thickness. The samples were analysed for both foraminifers (with a special focus on the planktonic species) and calcareous nannoplankton analyses. Foraminifera were extracted from disintegrated sediment in a warm solution of sodium carbonate (Na 2 CO 3 ); residue was sieved at 50 µm, 150 µm and 250 µm. Calcareous nannofossils have been studied in the fraction of 2-30 µm, separated by decantation method. Smear-slides have been analysed at an Olympus transmitting light microscope, with 1200x magnification. The occurrence of each species has been considered (Tables 1234in Supplementary materials) with respect to their distribution range in the biostratigraphic zonations [START_REF] Martini | Standard tertiary and quaternary calcareous nannoplankton zonation[END_REF][START_REF] Bolli | Oligocene to Holocene low latitude planktic foraminifera[END_REF]Perch Nielsen, 1985a,b;[START_REF] Berggren | Geochronology times scales and global stratigraphic correlation[END_REF][START_REF] Burnet | Upper Cretaceous[END_REF]Young, 1998;[START_REF] Olsson | Atlas of Paleocene planktonic foraminifera[END_REF][START_REF] Berggren | A revised tropical to subtropical paleogene planktonic foraminiferal zonation[END_REF][START_REF] Pearson | Atlas of Eocene planktonic foraminifera[END_REF][START_REF] Raffi | A review of calcareous nannofossil astrobiochronology encompassing the past 25 million years[END_REF][START_REF] Gradstein | The geologic time scale 2012[END_REF]. In addition, we particularly paid attention to some biostratigraphic markers displayed on Figures 8 and9, which benefit from a robust age of appearance/disappearance datums obtained by astronomical tuning of several cored long sections [START_REF] Raffi | A review of calcareous nannofossil astrobiochronology encompassing the past 25 million years[END_REF][START_REF] Gradstein | The geologic time scale 2012[END_REF]Zeeden et al., 2013). The studied samples are rich in specimens of planktonic groups of organisms. The main limit of this approach is the use of cuttings and not in situ data such as clabs or cores, unfortunately not enough available in the case of this study. Cuttings are subject to cavings at time of drilling. This means that for a given level microfossils of younger sediments can be mixed with in situ specimens. This implies that the age of the level that has to be dated must correspond to the oldest microfossils available. To strengthen the chronological model, we used the data of all the four studied and/or considered wells, some of them being subject to more cavings due to the quality of drilling or the type of microfossils. In some samples, the mixing of (caved, reworked,

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in situ) individuals of species of various ages is so high that we constrained the age with respect to equence stratigraphy (prism of low sea level or of high sea level) and then checked out which microfossils are consistent with it.

Analyses of calcareous nannoplankton were performed on all the studied samples (wells X1 and X3) with almost continuously consistent results. They were completed by analysis of planktonic foraminifera in some relatively uncertain intervals from the biostratigraphical viewpoint. The dated surfaces were first identified along seismic lines, as they must belong to the same reflector. In a second step, they are located on well-logs used for log drawings according depth velocity laws built for each wells. The surface age was defined using the oldest consistent microfossils identified along the surface of the two wells biostratigraphically studied (X1 and X3) plus some available unpublished biostratigraphic data already acquired on two other wells and provided by Total.

Orbital stratigraphy combined with seismic stratigraphy

The seismic stratigraphy study of the progradational Neogene sediments of the Zambezi delta shows the existence of stratigraphic depositional sequences organized in similar repetitive stratigraphic motif with a duration around 1 Myr (third order cycles). This is a characteristic feature of most of the world deltaic systems at that period (e.g. Baltimore Canyon Margin: [START_REF] Greenlee | Recognition and interpretation of depositional sequences and calculations of sea level changes from stratigraphic data-offshore New Jersey and Alabama Tertiary[END_REF]Moore, 1988, Carnavon Basin: Cathro et al., 2003..). Based on these observations, P.R. Vail and his group [START_REF] Bartek | Effect of Cenozoic ice-sheet fluctuations in Antarctica on the stratigraphic signature of the Neogene[END_REF] defined for the Neogene a world-scale pattern of third order sequences of eustatic origin due to ice volume variations at the base of the Exxon's chart (see [START_REF] Graciansky | Mesozoic and Cenozoic sequence stratigraphy of European Basins[END_REF].

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Since the 1990s and this idea of global eustatic third-order sequences for Mio-Pliocene times, three major advancements have been made. (1) Third order cycles are recognized as resulting from sea level variations of climatic origin related to the Earth orbital parameters variations (e.g. Strasser et al., 2000;[START_REF] Boulila | On the origin of Cenozoic and Mesozoic third-order eustatic sequences[END_REF][START_REF] Martinez | Orbital pacing of carbon fluxes by a 9 My eccentricity cycle during the Mesozoic[END_REF]. (2) These cycles are due to long-term eccentricity variations with frequencies of several million years, around 1.2, 2.4 and 9 Ma. Laskar [START_REF] Laskar | A long-term numerical solution for the insolation quantities of the Earth[END_REF][START_REF] Laskar | La2010: a new orbital solution for the long-term motion of the Earth[END_REF] The periods of low eccentricity correspond to cold climates, while high eccentricity periods correspond to warm climates. For pre-Pleistocene times and at the time-scale of few million years (see [START_REF] Hansen | Climate sensitivity, sea level and atmospheric carbon dioxide[END_REF], the cold climate periods are coeval to ice volume decrease (e.g. [START_REF] De Boer | Cenozoic global icevolume and temperature simulations with 1-D ice-sheet models forced by benthic δ 18 O records[END_REF] and then to sea level lowering (e.g. [START_REF] Miller | A 180-million-year record of sea level and ice volume variations from continental margin and deep-sea isotopic records[END_REF] and the contrary for the warm climate intervals.

Correlation between an eustatic curve and the stratigraphic record supposed to know the sedimentary flux [START_REF] Jervey | Quantitative geological modeling of siliciclastic rock sequences and their seismic expression[END_REF]. Both the MFS (maximum flooding surface) and the MRS (maximum regressive surface) occurred at time of balance between relative sea level rise and sediment supply/production. They cannot be used for correlation to a curve proxy of the sea level variations, as expected here. The only stratigraphic surfaces in marine environments controlled by the relative sea level variations and therefore independent of the sediment supply/production, are the correlative conformities (Fig. 2). These surfaces are formed during the relative sea level high and low periods. The time interval between the two correlative conformities corresponds, onshore to the erosion of the subaerial unconformity (SU) and, offshore to the formation of the

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forced regressive (FR) deposits. We here used as a time-line the first correlative conformity or sequence boundary, period of high relative sea level and onset of the unconformity The procedure of dating is a follow.

• Biostratigraphic dating of a single, or sets of, repetitive third-order depositional sequence(s) provide age ranges with a resolution of several million years.

• Use of Laskar's orbital solutions [START_REF] Laskar | La2010: a new orbital solution for the long-term motion of the Earth[END_REF] and, within the time range obtained from biostratigraphy, third order sequence boundaries (first correlative conformity) are correlated with the maxima of the Earth eccentricity.

• The date of the sequence boundary is the one of the maximum of Earth eccentricity calculated by Laskar.

Pollen and spore analysis and inferred palaeoprecipitation variations

At least one hundred pollen grains were counted per sample except in one very poor sample (Tables 56, Supplementary materials). Pollen grains were obtained after acid treatments using HCl, HF, and HCl again, followed by concentration in ZnCl 2 (at density 2.0) and sieving at 10 µm; a 50 µl volume of residue was mounted in glycerol and examined under a light microscope (magnification: x1000). One hundred and thirteen taxa 1 were identified in the ten samples from well X1, one hundred and twenty-eight taxa were identified in the twenty eight samples from well X1. They were gathered into eleven groups relative to the main types of the modern vegetation of Africa, represented today along the Zambezi catchment. Botanical identification of pollen grains is for long used in Quaternary and Neogene records thanks to a detailed morphological examination of fossil pollen and comparison with pollen databases of 1 A taxon (pl. taxa) is an entity in Systematics that may be a family, a genus or a species (Suc et al., 2004). It has been established that the same approach is also suitable for Paleogene deposits (Suan et al., 2017).

Pollen flora of well X1 concerns in a discontinuous record the late Oligocene and late Miocene clayey sediments of continental origin (Figs. 67). Studies on modern sediments from the Grand Rhône Delta (SE France) show that pollen grains recorded in such deltaic to protodeltaic sediments are almost exclusively transported by the river [START_REF] Cambon | Modern pollen deposition in the Rhône delta area (lagoonal and marine sediments), France[END_REF] and are highly representative of the vegetation of the catchment basin (Beaudouin et al., 2005a).

Studies on recent Quaternary similar sediments from the Gulf of Lions (offshore SE France) evidenced weak reworking of palynomorphs (i.e. pollen grains and spores) during phases of high sea level, increasing during phases of sea-level fall (Beaudouin et al., 2005b). Pollen flora of well X3 comes from late Miocene to middle Pleistocene hemipelagic shales and silts (Figs. 67).

Researches done on modern deeper deposits in an area influenced by a powerful river such in the Gulf of Lions may guide our interpretation of pollen record of well X3: sediments from the shelf and slope are rich in pollen grains without sorting by marine currents that makes the signal understandable and reliable where reworking is detected with respect to preservation and colour (Beaudouin et al., 2007a,b); pollen signal from recent turbidites of the Rhône Neofan (Gulf of Lions) appeared not much disturbed by comparison with a shelf pollen record, despite more intense reworking in relation with phases of low sea level (Beaudouin et al., 2004). In addition to ancient morphological types obviously reworked, palynomorphs of wells X1 and X3 have been considered as reworked when they were poorly preserved or affected by a dark colouring (Tables 56, Supplementary materials Pollen grains affected by caving cannot be detected because of the The modern catchment of the Zambezi River displays a large variety in vegetation resulting from strong climate contrasts between the west, arid -the Kalahari Desert -and the east, very humid around the Malawi Lake (Fig. 3). From the thermal viewpoint, some patches of tropical rain forest persist in spite of human activity in addition to the mangrove on the coastline, that contrasts with few relict areas with Afromontane forest the representation of which is impossible at the scale of the map (Fig. 3).

In Tables 56(Supplementary materials displaying the detailed pollen records from wells 1 and 3 respectively, taxa have been grouped according to their ecological significance in eleven groups representative of the regional vegetation types (Fig. 3). These groups allow drawing the synthetic pollen diagrams shown in Fig. 11, their respective percentages are calculated on the total pollen sum (Tables 56, Suppl. mat.). Such diagrams contribute to define a dominant climate in the region according to the prevalent pollen-ecological groups.

In the case of rather constant relative frequencies of the pollen groups as shown in the synthetic pollen diagrams of wells 1 and 3 (Fig. 11), calculation of pollen ratios between climatically opposed taxa or groups of taxa may be used to spotlight some variations difficult to evidence [START_REF] Cour | La signification climatique, édaphique et sédimentologique des rapports entre taxons en analyse pollinique[END_REF]. Such ratios are seldom used in African palynology [START_REF] Dalibard | High-resolution vegetation history of West Africa during the last 145 ka[END_REF]. In the pollen record of wells 1 and 3, it appeared worthwhile to consider the pollen ratio tropical rain forest + warm-temperate semi-deciduous forest + pioneer forest / sparse forest to wooded savannah + dry grassland to open savannah, i.e. low altitude forest vegetation (humid context) vs. open vegetation (dry context). Taking into account the important contrast in humidity between these assemblages, the ratio can be regarded as a Humidity Index (HI). Its values ≤1

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12 mean drier climatic conditions while those ≥1 mean more humid ones. This HI cannot be directly calibrated in terms of annual rainfall because we have no surface pollen records from different climatic areas of the catchment basin. However, DeBusk (1997) realised pollen analysis of surface samples of Lake Malawi located at about 500 m in altitude. A rough calculation on this record of the pollen ratio between evergreen forest / grassland shows a strong contrast between the northernmost part of the lake covered by forests and its southernmost part inhabited by wooded savannah (Timberlake, 2000). To the north where precipitation is of ca. 2400 mm/yr, the ratio would range from 0.133 to 0.555. To the south where precipitation is lower than 800 mm/yr, the ratio would range from 0.042 to 0.077.

Geological setting

The Zambezi Delta is located along the northern Mozambican Margin, which is bounded by two major transform fracture zones (F.Z.) (Fig. 1A), the Mozambique F.Z. to the west and the Davie Ridge or Davie F.Z. to the east. The Zambezi Delta is bounded in the south by the Beira High and passes laterally into a deep-sea plain, the Angoche Basin (Fig. 1A).

Geodynamic setting

The Mozambique Margin is the result of the Mozambique oceanic domain opening between Africa and Antarctica during the Gondwana break-up. The age of the first oceanic crust is still debated, with a range from 155.3 Ma (M26) [START_REF] Jokat | Timing and geometry of early Gondwana breakup[END_REF][START_REF] Konig | Advanced insights into magmatism and volcanism of the Mozambique Ridge and Mozambique Basin in the view of new potential field data[END_REF] to 166 Ma (M41) [START_REF] Leinweber | The crustal structure of the Central Mozambique continental margin -Wide angle seismic, gravity and magnetic study in the Mozambique Channel, Eastern Africa[END_REF][START_REF] Leinweber | The Jurassic history of the Africa -Antarctica corridor -new constraints from magnetic data on the conjugate continental margins[END_REF], i.e. the Late Jurassic. The Beira High is a 280 km long and 100 km wide continental topographic structure that runs parallel to the coast [START_REF] Konig | Advanced insights into magmatism and volcanism of the Mozambique Ridge and Mozambique Basin in the view of new potential field data[END_REF][START_REF] Mueller | The crustal structure of Beira High, central Mozambique -Combined investigation of wide-angle seismic and potential field data[END_REF], dividing the Zambezi sedimentary

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13 system into a proximal part including the deltaic domain and the Zambezi depression, and a distal part corresponding to turbidite deposits.

Onshore, the Zambezi catchment drains a large area from the northern boundary of the South African Plateau (Thomas and Shaw, 1988) to the southern portion of the EARS, including the eroded aborted Karoo Rifts (Luangwa, Cabora Bassa, Mid-Zambezi) and active Neogene Rifts (Malawi/Shire). The Zambezi River path is subdivided into three major segments with specific geomorphic characteristics [START_REF] Moore | The Zambezi River[END_REF]. Upper Zambezi, which extends from the headwaters to Victoria Falls; Middle Zambezi, which extends from the Falls to the edge of the Mozambique coastal plain, corresponding to the Cabora Bassa Gorge; and, Lower Zambezi, which is located along the coastal plain (Fig. 1B).

This segmentation results from topographic changes in the Zambezi in response to three main deformation events that have occurred since the Cretaceous [START_REF] Moore | The Zambezi River[END_REF] caused by uplifts of the South African Plateau and the EARS (Fig. 4).

• The initial uplift of the South African Plateau in the Late Cretaceous, which most likely induced a flexure from the Limpopo to Zambezi Rivers, as identified by Du Toit (1933) and later described by [START_REF] Moore | A reappraisal of epeirogenic flexure axes in southern Africa[END_REF] as the Okavango-Kalahari-Zimbabwe high. Apatite fission track analysis (AFTA) recorded this event in southern Africa (e.g. [START_REF] Gallagher | The Mesozoic denudation history of the Atlantic margins of southern Africa and southeast Brazil and the relationship to offshore sedimentation[END_REF]Van Der Beek et al., 2002)), showing a main denudation event and an increase in the amount of sediment [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]. • The third event corresponds to the progressive southward migration of the EARS since the Oligocene [START_REF] Chorowicz | The east African rift system[END_REF][START_REF] Macgregor | History of the development of the East African Rift System: a series of interpreted maps through time[END_REF] coeval with an increase in topography roughness and relief [START_REF] Pik | Timing of East African Rift development in southern Ethiopia: Implication for mantle plume activity and evolution of topography[END_REF]. The EARS is subdivided into a western branch, which crosses Mozambique and delimits the Rovuma and Victoria plates from the African plate, and an eastern branch, which crosses Tanzania and spreads into the Mozambique Channel through the Davie Ridge [START_REF] Mougenot | Seaward extension of the East African Rift[END_REF]. It delimits the Rovuma from the Somalian plates.

Uplift of the EARS began in its eastern branch (in Ethiopia) during the Oligocene-Miocene, with long-wavelength topographic growth contemporaneous with Oligocene volcanic activity (LIP, Couli et al. (2003) overlapping the Ethiopian Rift shoulders [START_REF] A N U S C R I P T A C C E P T E D Accepted Manuscript 51 Pik | Stability of the Upper Nile drainage network (Ethiopia) deduced from (U-Th)/He thermochronometry: implications for uplift and erosion of the Afar plume dome[END_REF][START_REF] Pik | Timing of East African Rift development in southern Ethiopia: Implication for mantle plume activity and evolution of topography[END_REF].

The initial western branch of the EARS developed during the middle Miocene [START_REF] Macgregor | History of the development of the East African Rift System: a series of interpreted maps through time[END_REF] with the formation of Lake Albert at about 17 Ma (Simon et al., 2017), the central Tanganyika Rift at approximately 9-12 Ma [START_REF] Cohen | Estimating the age of formation of lakes: an example from Lake Tanganyika, East African Rift system[END_REF], and the Malawi Rift most likely at 8.6 Ma (Songwe tuff ) (Ebinger, 1989;Ebinger et al., 1993). More recently, thermochronological data recorded a regional uplift dated at 2.5 Ma [START_REF] Macphee | Exhumation, rift-flank uplift, and the thermal evolution of the Rwenzori Mountains determined by combined (U-Th)/He and U-Pb thermochronometry[END_REF]Bauer et al., 2016) and K/Ar volcanic activity dating (Ebinger et al., 1993) from the Albert Rift to the North Malawi Rift. This major tectonic activity since the Oligocene has shaped a 6000 km elevated area [START_REF] Chorowicz | The east African rift system[END_REF] that is oriented mainly north-south with a medium wavelength crest that reaches 1500-5100 m.

Margin infilling

The Zambezi sedimentary record is assumed to have started during the Late Jurassic, deposited over Karoo volcanics in the Early Jurassic (Salman and Abdula, 1995) (Fig. 4). The

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15 Late Jurassic sediments are continental sandy red-beds distributed mainly along buried grabens.

Cretaceous rocks are terrigenous sediments deposited in continental and shallow marine environments (Sena, Domo (Lower and Upper), and Lower Grudja Fm). Cenozoic deposits are predominantly marine and deltaic (Salman and Abdula, 1995) (Fig. 4). The Paleogene is characterized by a shallow, mixed marine platform (Upper Grudja Fm), the Eocene by a carbonate platform (Cheringoma Fm). The base of Oligocene corresponds to the initiation of the two main present-day deltaic systems, the Limpopo and the Zambezi Deltas (Salman and Abdula, 1995).

Climate setting

Several methods have been used to study changes in the East African paleoclimate: computer modelling (Sepulchre et al., 2006); analysis of sedimentary rocks such as bauxites or evaporites (Scotese et al., 1999;[START_REF] Burke | The African erosion surface: a continental-scale synthesis of geomorphology, tectonics, and environmental change over the past 180 million years[END_REF][START_REF] A N U S C R I P T A C C E P T E D Accepted Manuscript 49 Morley | Cretaceous and Tertiary climate change and the past distribution of megathermal rainforests[END_REF] and analysis of palaeobotanical data such as leaves (Jacobs and Winkler, 1992;Jacobs and Herendeen, 2004), fruit [START_REF] Chesters | The Miocene flora of Rusinga Island, Lake Victoria, Kenya[END_REF], pollen grains (Vincens et al., 2006;[START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF][START_REF] Rasmussen | Middle -late Miocene palaeoenvironments, palynological data and a fossil fish Lagerstatte from the Central Kenya Rift (East Africa)[END_REF], and wood [START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF]. In addition, several studies analysed leaf morphology to quantify palaeoprecipitation [START_REF] Jacobs | Estimation of low-latitude paleoclimates using fossil angiosperm leaves: examples from the Miocene Tugen Hills, Kenya[END_REF]Jacobs and Herendeen, 2004). Most studies are based on scattered outcrops in northeast Africa; only [START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF] provides a continuous curve of vegetation associations characteristic of climate zones, based on pollen record from well DSDP 231 (Gulf of Aden). These discontinuous data hinder understanding of climate change in an active tectonic setting in which local vegetation is the result of interactions between topography and climate (Jacobs et al., 2010). Thus only major climate trends can be identified:

M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 16 Paleocene :
The Paleocene was a wet and warm period characterised by a widespread megathermal rainforest or monsoon forest (Morley, 2011) and lateritic rocks from 23°N to 23°S latitude [START_REF] Burke | The African erosion surface: a continental-scale synthesis of geomorphology, tectonics, and environmental change over the past 180 million years[END_REF].

Eocene : The Eocene corresponds to the wettest and warmest period of the Cenozoic, with deep sea water temperatures 10°C higher than those of the present day (Zachos et al., 2001). As in the Palaeocene, a megathermal rainforest or monsoon forest covered most of Africa [START_REF] Burke | The African erosion surface: a continental-scale synthesis of geomorphology, tectonics, and environmental change over the past 180 million years[END_REF][START_REF] A N U S C R I P T A C C E P T E D Accepted Manuscript 49 Morley | Cretaceous and Tertiary climate change and the past distribution of megathermal rainforests[END_REF]. However, palynological data indicate that woodlands existed in Tanzania during the Lutetian at 46 Ma [START_REF] Herendeen | Fossil legumes from the middle Eocene (46.0 Ma) Mahenge flora of Singida, Tanzania[END_REF]Jacobs and Herendeen, 2004), which challenges the idea of a permanent megathermal forest over Africa [START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF].

Oligocene : T h e O l i g o c e n e defined at its outset by global climate change, with the growth of the Antarctic ice sheet and a 5°C decrease in deep-sea water temperatures (Zachos et al., 2001), which initiated an icehouse period. Locally, palynological data indicate the presence of moist forests in Ethiopia in the Chattian (Jacobs and Herendeen, 2004;Jacobs et al., 2005;[START_REF] A N U S C R I P T A C C E P T E D Accepted Manuscript 50 Pan | The fossil history of palms (Arecaceae) in Africa and new records from the late Oligocene (28 -27 Mya) of north-western Ethiopia[END_REF]. However due to the lack of outcrops of this age over larger geographic areas, the extent and sustainability of this climate belt in East Africa is uncertain [START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF].

Miocene :

The Miocene is characterised by a climatic temperature optimum between 14.7 and 17.0 Ma (Langhian, Zachos et al., 2001) and rapid global cooling (Serravallian) caused by growth of a permanent Antarctic ice sheet (Zachos et al., 2001). East Africa experienced widespread aridification in the early to middle Miocene. The growth of relief and high volcanic activity related to the EARS is assumed to have created great variability and spatial heterogeneity in vegetation, with wet forests above drier plains and rain shadow effects that dried vegetation [START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF]. For the late Miocene, based on the continuous record of well DSDP 231 (Gulf [START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF] highlights three pulses of grassland vegetation and one episode of reduction in pollen richness corresponding to the occurrence of wet events at 10.5, 7.0 and 5.5

M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 17 of Aden),
Ma and an arid event at 6.5 Ma, respectively.

Pliocene : At world-scale the early Pliocene (5.3-3.6 Ma -Zanclean) is a warm period with two cooling (glaciation) events around 4.9-4.8 Ma and 4 Ma [START_REF] De Schepper | A global synthesis of the marine and terrestrial evidence for glaciation during the Pliocene Epoch[END_REF]. The cooler upper Pliocene (Piacenzian) is punctuated by a warm period known as the Mid-Piacenzian (former mid-Pliocene) Warmth (or Warm Period) between 3.25 and 3.05 Ma (e.g. [START_REF] A N U S C R I P T A C C E P T E D Accepted Manuscript 52 Prescott | Assessing orbitally-forced interglacial climate variability during the mid-Pliocene Warm Period[END_REF]. The early Pliocene is an African-scale humid event (e.g. [START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF].

Pleistocene : The Pliocene -Pleistocene transition is a major cooling, followed at the earlymiddle Pleistocene transition (0.8-0.9 Ma) by a change in the climatic record of the prevailing influence of obliquity in the orbital cycles (41 kyrs) during the early Pleistocene replaced by that of eccentricity (100 kyrs) after. Historically, these variations were recorded in the peri-Sahara marine domains with the record of aeolian dusts in West and East Africa sediments (Tiedemann et al., 1994;[START_REF] Demenocal | Plio-Pleistocene African climate[END_REF].

Results

Seismic stratigraphy (Fig.5-7)

Two types of depositional profiles were observed: a margin delta (most of the basin infilling) and a carbonate ramp. The profile of the margin delta changed over time, with an increase in height and steepness of clinoforms from the Cretaceous to the present day (from 80 to ∼1400 m). The flat upstream portion (undaform or topset) consists of flat relatively continuous parallel to slightly divergent reflectors (Fig. 5). Calibration of the well logs and cuttings suggests that they are either continental deltaic plain deposits passing upstream to alluvial The carbonate ramp (sequences S7 and S6 -Figs. 67) is poorly documented on cuttings and outcrops (it crops out upstream in the Cheringoma Plateau; Fig. 1). It is made up of muddy limestones (calcilutites -mudlog descriptions) passing upstream to higher energy bioclastic facies (calcarenites -mudlog descriptions).

At least three orders of sequences (Figs. 67) were defined that require confirmation using the age model (see discussion above). The possible third order sequences, which are well recorded in the Oligocene-Neogene wedge (based on previously published ages see above), are repetitive stratigraphic motives. Seventeen sequences were defined and classified from the most recent (Pl.0, Pl.5) to the oldest (M1, M.11). Four main sub-units were defined, which correspond in part to system tracts:

• Gravitary deposits part of the of the FSST and/or LST onlap the unconformity at the toe of the clinoform. These deposits are either shallow turbidite lobes (see description above) along slope aprons or MTC.

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19

• FR or FSST and LNR or LST deposits, were difficult to distinguish one from other. Most of these wedges are progradational-agradational indicating LNR or LST. Few periods of accommodation removal corresponding to FR or FSST are preserved. This is likely due to the large amount of subsidence created beneath the delta, which is often greater than the accommodation removal due to eustasy.

• Transgressive deposits (T or TST) which are retrogradational, highly aggradational wedges.

• A few well-preserved HNR deposits, whose dominant feature is the TST. Most are recorded by a single reflector below the unconformity or are eroded by the latter.

Potential second order unconformity-bounded sequences (Figs. 6-7) were defined above the main world-scale marine flooding of the Cenomanian-Turonian boundary (based on previously published ages see above). The sequences were classified from the most recent (S0) to the oldest (S8):

• Sequence S8 is mainly composed of siltstones. Offlap breaks were difficult to identify. The deposits present destabilization features and numerous erosion surfaces are observed.

• Sequence S7 is a mixed siliciclastic (mainly siltstones) carbonate (coarse grained bioclastic sands) ramp corresponding to the Upper Grudja Fm (Salman and Abdula, 1995), with offlap breaks that were difficult to identify. Oceanic current activity is substantial, as indicated by the numerous erosion surfaces along the distal ramp that increase toward the eastern portion of the Beira High.

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• Sequence S6 is mainly a carbonate ramp with sediments that are finer grained than those in S7, with still active erosion and transport by ocean currents. It corresponds to the Cheringoma Fm (Salman and Abdula, 1995). A large contourite mound was created along the Beira High.

• Sequence S5 is bounded by the largest unconformity in the entire existence of the delta, with incisions along the shelf (flat-bottom incised valleys), the ramp/slope (canyons) and the deepest part of the system (contourite incised channels). Many older Eocene fauna are reworked in the sediments just above this unconformity. This is the birth of the modern delta, with a typical deltaic depositional profile. The clinoforms become higher, ranging from 650-900 m. Third order sequences are difficult to identify in this mainly progradational sequence consisting of coarse-grained sand upstream and silt downstream.

• Sequence S4 (third-order sequence: M.11) is bounded by the second largest truncated unconformity underlying progradational wedges and with a major onlap of the overlying sediments. This sequence is relatively thin (200 ms) and eroded along the Beira High by large contourite incisions.

• Sequence S3 (third-order sequences: M.10 to M.1) is bounded by an erosional unconformity truncating older inner deposits. The deltaic clinoforms progressively grow to more than 1000 m. This mainly progradational sequence is characterised by a FR wedge above the unconformity. This is the time of emplacement of the first shallow turbiditic wedges at the base of clinoforms. The first MTC occurred. The upstream sediments are coarse to mediumgrained sands.

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21

• Sequence S2 (third order sequences: Pl.5 to Pl.3), mainly progradational and aggradational, consists mainly of fine to medium grained sands and silts. The clinoforms range in height from ∼1000 to ∼1300 m, and MTCs are more common.

• Sequence S1 (third-order sequences: Pl.2 to Pl.0), mainly progradational and aggradational, is the growth period of the modern depositional profile (with clinoforms higher than 1400 m).

MTCs are the dominant gravity deposits.

A first order cycle, or continental encroachment cycle (e.g. [START_REF] Graciansky | Mesozoic and Cenozoic sequence stratigraphy of European Basins[END_REF], was defined. However Cenozoic uplifts eroded the upstream portion of the margin, which made it difficult to identify major marine floodings. Two plausible candidates are the MFS of the Cenomanian-Turonian boundary or sequence S6 (Cheringoma Fm). Geometrically, the trend is progradational to aggradational during the earliest Cretaceous from the basement to the sequence boundary Uc2 then clearly retrogradational until the MFS of the Cenomanian-Turonian boundary. It is more aggradational from the latter to the MFS of sequence S6, and it is progradational-aggradational from the MFS of sequence S6 to the seafloor forming the famous Oligocene-Neogene wedge characteristic of the Zambezi Delta.

Age model

Two types of age models were developed. For the Late Cretaceous and Paleogene, ages were based only on biostratigraphy (Figs. 67) (planktonic foraminifera and calcareous nannofossils -figs. 8-9). For the Neogene, a true age model was developed based on biostratigraphy (using the same proxies) and orbital stratigraphy combined with seismic stratigraphy (Fig. 10). According to the fact that the age of a formation might be at the early or latest time range of the biozone, minimum and maximum age ranges of the sequence boundary have to be defined. Here the minimum range is between 57.7 and 57.0 Ma and the maximum between 48.2 and 45.7., i.e. late Thanetian to early Lutetian. Considering the sequence S6 thickness evolution from wells X to X3, we suggest to set the age using a well with high sedimentation rate, i.e X3. A late Thanetian to early Ypresian age is most probable (57.7-54.5 Ma, i.e. NP9-NP10 biozones).

Late Cretaceous to Paleogene

• Regarding to the planktonic foraminifera, the sequence boundary of sequence S5 (base of the deltaic complex) is dated between zones E15-E14 and E14 (X3), intra zone E15-E9 (well X2) intra zone E14 (well X1); and between NP20-NP19 and NP18 zones (well X3), intra NP 17 zone (X1) for what concerns calcareous nannofossils. Based on the same principles than for S6, the age of the oldest underlying formation refers to zone E9 and the one oldest overlying formation belongs to zone E15 . Because of the condensed toes of deltaic clinoformes observed on X2 and X3, we suggest to base the age on a well drilled in the deltaic clinoforms where the sedimentation rate is higher (X1). In that case, the ages of the oldest underlying formation and of the oldest overlying formation fall into the same biozones i.e. E14 (36.2-38.2 Ma, latest Bartonian to early Priabonian). It cannot be younger than the Eocene-Oligocene boundary (33.9 Ma) as previously expected by different authors (e.g. Salman and Abdullah, 1995).

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24

• The sequence boundary of sequence S4 is dated between zones O1-2 and M1-O7 (well X2) according to (planktonic foraminifera); and between NP25 and NN7 zones (well X1) and zones NP25 and NN4-5 (well X3) according to calcareous nannofossils.

Neogene

Several age ranges were provided by calcareous nannofossils ticking either single or sets of third order cycles. These ages provide possible ranges for the equivalences with the Laskar's orbital solutions and therefore the age calibration of the third order sequence boundaries. The first satisfying result is that we got the same number of sequences on the Laskar's orbital solutions than the observed third order sequences using the ages provided by biostratigraphy. Base of sequence M7 (also base S3 sequence boundary) is dated at 11.9 Ma, and so on for base of M6 at 10.7 Ma, M5 at 9.9 Ma, M4 at 9.0 Ma, M3 at 8.4 Ma, M2 at 7.8 Ma, M1 at 7.0 Ma, Pl. However, few weak variations are perceived. An interesting point is the variations of the elements of the Afromontane forest, mainly composed of Podocarpus that indicates the occurrence of high relief in the region. Their slight increase in the early Chattian, mid-Tortonian, late Zanclean and especially Calabrian (Fig. 11) may result from descent of this vegetation belt in relation with some cooling (e.g. [START_REF] Dalibard | High-resolution vegetation history of West Africa during the last 145 ka[END_REF], perhaps associated with a more intense activity of the river in altitude. Noteworthy is also the maximum of mangrove elements during Chattian and early Tortonian, probably in relation with warmer conditions and highstand of sea level [START_REF] Poumot | Palynological evidence for eustatic events in the tropical neogene[END_REF].

The most relevant proxy is the above defined Humidity Index (HI). Unfortunately the number of samples is quite limited for the late Oligocene and for the late Miocene. This is explained by the origin of the concerned samples within the condensed deposits of the toes of clinoforms. Obviously, late Oligocene (Chattian) is the most humid period of all the studied time

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26 interval with values of HI comprised between 0.6 and 0.9 in well X1, that suggests yearly rainfalls of ca. 2000 mm. It occurred after a little aridification around the Eocene-Oligocene boundary compared to the very humid conditions prevailing up to Lutetian [START_REF] Braun | Rapid erosion of the Southern African Plateau as it climbs over a mantle superswell[END_REF].

Humidity was important again during Tortonian when HI values reached 0.75 in well X1. It is to be pointed out that the maxima of HI in the coastal well X1 are higher than those in the distal well X3, probably because of the lesser concentration in arboreal pollen grains towards the basin.

After an aridification during the uppermost Miocene -lowermost Pliocene (?), humidity increased again during the late Pliocene with HI values reaching a maximum at 0.255 in well X3, but this phase was not so humid as the Chattian and Tortonian phases. Following repeated more arid conditions, the Gelasian-Calabrian period was more humid too with after all maximum HI values lower than 0.1. Apart from the more humid episodes, HI ranges between 0.2 and 0.3 in well X1 and 0.01 and 0.05 in well X3, revealing annual precipitation below 800 mm.

Discussion

5.1. Regional (lithosphere deformation) vs. global (eustasy/climate) controls of the second order sequences (Fig. 12)

The second order sequences are controlled as all the depositional sequences by accommodation space variations [START_REF] Jervey | Quantitative geological modeling of siliciclastic rock sequences and their seismic expression[END_REF] that can be either tectonic (vertical component of the lithosphere deformation) or eustatic (of tectonic or climatic origin). For the Cenozoic time interval studied, the eustatic variations are increasingly influenced by the climate over time, mainly after the Eocene-Oligocene transition, with the onset of an icehouse period and the growth of glaciers in Antarctica (e.g. [START_REF] A N U S C R I P T A C C E P T E D Accepted Manuscript 48 Miller | A view of Antarctic ice-sheet evolution from sea-level and deep-sea isotope changes during the Late Cretaceous -Cenozoic[END_REF]. Nevertheless, some authors, based on detailed subsidence analysis of well-dated basins, suggested that second order sequences are of tectonic origin, recording accelerating-decreasing variations in subsidence rates (e.g Vail et al. 1991). We • S8 sequence boundary (around the Santonian-Campanian boundary, i.e. 86.3 Ma) does not correspond to any major climatic cooling that might control a climatic eustatic fall at the origin of an unconformity [START_REF] Friedrich | Evolution of middle to Late Cretaceous oceans -a 55 my record of Earth's temperature and carbon cycle[END_REF]. It is more likely the end of a cool period.

However, the Late Cretaceous is a period of extremely long wavelength (several thousands of kilometres km) lithosphere deformation that is influenced by mantle dynamics (e.g. [START_REF] Nyblade | The African Superswell[END_REF][START_REF] A N U S C R I P T A C C E P T E D Accepted Manuscript 44 Gurnis | Constraining mantle density structure using geological evidence of surface uplift rates: The case of the African superplume[END_REF]De Wit,2007) • S7 sequence boundary (around the Cretaceous-Paleogene boundary, 67.3-63.2 Ma) is a regional-scale unconformity that extends throughout southern Africa and has a tectonic origin linked to the growth of the South African Plateau [START_REF] Baby | Uplift history of a transform margin revealed by the stratigraphic record: The case of the Agulhas transform margin along the Southern African Plateau[END_REF]. However, its deformation processes are insufficiently understood. Eustatic origin cannot be inferred; the Cretaceous-Paleogene boundary is the onset of major warming and therefore major sea level rise [START_REF] Friedrich | Evolution of middle to Late Cretaceous oceans -a 55 my record of Earth's temperature and carbon cycle[END_REF].

• S6 sequence boundary (late Thanetian to early Ypresian, 57.7-54.5 Ma), is marked by two carbonate platforms, the oldest is mixed siliciclastic (Upper Grudja Fm), while the youngest

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28 contains only carbonates (Cheringoma Fm). Determining a tectonic origin is difficult, as there is no evidence of local or regional angular unconformity or a siliciclastic event. At the global scale, the uppermost Thanetian is a major period of sharp cooling (Zachos et al., 2001) before the PETM and the overall warming of the Ypresian Early Eocene Climatic Optimum. We suggest that the base S6 unconformity can be the eustatic decrease in sea level before the uppermost Thanetian cooling/low sea level.

• S5 sequence boundary (latest Bartonian to early Priabonian, 38.2-36.2 Ma) corresponds to the initiation of the modern deltaic system of the Zambezi River. An unconformity occurring around the Eocene-Oligocene boundary has been characterized all around Africa and due to a major continent-scale uplift related to mantle dynamics [START_REF] Burke | The African erosion surface: a continental-scale synthesis of geomorphology, tectonics, and environmental change over the past 180 million years[END_REF].

Nevertheless, because of its age (around the Eocene-Oligocene boundary) and wide occurrence at Africa-scale, its cause is debated and rather related to climatic and oceanographic changes (e.g. Séranne, 1999). Our age results indicate that this unconformity occurred before the Eocene-Oligocene climate change and therefore cannot be related to the associated major sea-level fall of approximately 100 m [START_REF] A N U S C R I P T A C C E P T E D Accepted Manuscript 48 Miller | A view of Antarctic ice-sheet evolution from sea-level and deep-sea isotope changes during the Late Cretaceous -Cenozoic[END_REF][START_REF] De Boer | Cenozoic global icevolume and temperature simulations with 1-D ice-sheet models forced by benthic δ 18 O records[END_REF]. In the south-eastern portion of the South African Plateau along the Durban Basin and the Kwazulu-Maputaland Margin, [START_REF] Baby | Uplift history of a transform margin revealed by the stratigraphic record: The case of the Agulhas transform margin along the Southern African Plateau[END_REF] • S3 The base S3 sequence boundary (11.6 Ma, base of Tortonian) does not correspond to the major climate cooling in the second half of the Miocene that occurred during the Serravallian (around 13 Ma). It is related to the formation of the modern EARS, even though the timing of these events is not well dated [START_REF] Macgregor | History of the development of the East African Rift System: a series of interpreted maps through time[END_REF]Simon et al., 2017).

• S2 sequence boundary (5.6 Ma, uppermost Messinian) is both a major tectonic reorganization of the EARS and of the climate. From a climate viewpoint, this is a major humidification event, from drier to wetter conditions (Fig. 11; [START_REF] Bonnefille | Cenozoic vegetation, climate changes and hominid evolution in tropical africa[END_REF]. The latest Miocene marks the formation of the Rukwa Rift and portions of the northern Malawi Rift. This is the end of the first phase of the Runkwe Volcanic Province (at the transition between the Rukwa and Malawi Rifts; [START_REF] Fontijn | The Rungwe Volcanic Province, Tanzania -A volcanological review[END_REF]. This is a major change in the subsidence regime in the Albert Rift (Simon et al., 2017). This indicates a major reorganisation of drainage in the Malawi that likely extended far north before this event. It is difficult to assess what is due to lithosphere deformation vs. changes in precipitation; the latter most likely enhanced the former.

• S1 sequence boundary (2.8 Ma, latest Piacenzian) is a period of lithosphere deformation and climate change. In the EARS, it corresponds to the paroxysmal phase of the Rungwe Volcanic Province [START_REF] Fontijn | The Rungwe Volcanic Province, Tanzania -A volcanological review[END_REF] and, although it is unclear, the uplift of the northern

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ACCEPTED MANUSCRIPT 30 end of the Malawi Rift and an increase in subsidence to the south (Ebinger et al., 1993). From a climatic point of view this is the beginning of the glacial phases of the Pleistocene in the Northern Hemisphere (2.6 Ma). Again a climatically enhanced tectonic unconformity is the most probable.

The palaeoprecipitation record of the Zambezi Delta in the frame of the East African climate Cenozoic changes.

As already mentioned the palaeoprecipitation record of Africa is based mainly on local discontinuous outcrops of sediments dated with varying degrees of accuracy. This is also true for EARS sediments, in which the stratigraphic record consists of continental sediments interstratified within thick volcanic rocks. The only continuous records come from wells in the Aden Gulf (DSDP Site 261: Bonnefille, 2010) and offshore of Namibia (ODP site 1085; e.g. Dupont et al., 2011) in north-eastern and southern Africa, respectively.

The methods of palaeoprecipitation reconstructions are pollen assemblages, morphology of leaves (e.g. [START_REF] Jacobs | Estimation of low-latitude paleoclimates using fossil angiosperm leaves: examples from the Miocene Tugen Hills, Kenya[END_REF], the structure of trunks (e.g. De [START_REF] De Franceschi | Fossil wood from the upper Miocene Mpesida Beds at Cheparain (Baringo District, Kenya): Botanical affinities and palaeoenvironmental implications[END_REF], the type of palaeosoils (e.g. [START_REF] Retallack | Paleosols and paleoenvironments of the middle Miocene, Maboko Formation, Kenya[END_REF] or are based on vertebrate associations (the number of herbivore fossils) or isotope geochemistry (the ratio between C3 proxy of woodlands vs. C4 proxy of grasslands). We here proposed a compilation (Fig. 11) of the palaeoprecipitation record of East Africa using both published data and our results offshore Zambezi Delta.

The Oligocene climate in Africa is not well known. In northern Africa, aridification is recorded around the Eocene-Oligocene boundary, with a change from a tropical forest (Eocene) to more arid conditions with dry or semi-arid forests (early Oligocene) (e.g. [START_REF] Louvet | Contribution à l'étude de la mise en place des forêts tropicales africaines[END_REF][START_REF] Biondi | Bois fossiles et végétations arborescentes des régions méditerranéennes durant le Tertiaire[END_REF]. In Ethiopia (north of Lake Tana), late Oligocene flora and palaeosoils (Jacobs et (precipitation greater than 1100 mm/yr). Southward along the Rukwa Rift, late Oligocene woods [START_REF] Damblon | Identification of a fossil wood specimen in the Red Sandstone Group of south-western Tanzania: stratigraphical and tectonic implications[END_REF], redated by Roberts et al., 2010) are typically tropical, with possible precipitation ranges from 1450-1750 mm/yr. These data indicating tropical warm and humid conditions during the late Oligocene in East Africa are confirmed by our data that suggests humid conditions along the Zambezi catchment during this time interval.

In Austral Africa (Atlantic side of Western Cape) palynological and biogeochemical studies indicate that in the early to middle Miocene, at the scale of astronomically driven climate change (Milankovitch cycles), alternating subtropical and warm temperate conditions occurred [START_REF] Roberts | Miocene fluvial systems and palynofloras at the southwestern tip of Africa: Implications for regional and global fluctuations in climate and ecosystems[END_REF] in an overall trend of cooler and drier conditions (Sciscio et al., 2016).

Northward along the Atlantic Namibian Margin where the present day Namib Desert is located, the first evidence of aeolian sediments (Namib Desert) are dated from the late early Miocene ( 16Ma; [START_REF] Pickford | New Ratite eggshells from the Miocene of Namibia[END_REF]. Silicified wood and vertebrate fauna in the early Miocene Orange terraces Burdigalian) suggest subtropical open woodlands [START_REF] Neumann | Shaping of modern southern African biomes: Neogene vegetation and climate changes[END_REF].

Isotopic studies of ratite eggshells preserved in aeolian sediments (Segalen et al., 2006) indicate homogeneous climate conditions during the Miocene, which was less arid than the present day and may have had winter precipitation. This aridification is related to the position of the Benguela Current and associated upwellings (Siesser, 1980;[START_REF] Diester-Haass | Miocene history of the Benguela Current and Antarctic ice volumes: Evidence from rhythmic sedimentation and current growth across the Walvis Ridge (Deep Sea Drilling Project Sites 362 and 532)[END_REF] In East Africa, north of the Kenyan Dome (Lokichar Basin) and around the Oligocene-Miocene boundary, palynological data (Vincens et al., 2006) suggest wet conditions (1200-1600 mm/yr) with a dry season in a mosaic of semi-deciduous forests and humid wood-lands. Later (early Miocene) and southward along the East African Dome around the Napak District (Uganda, 20.0-18.5 Ma;[START_REF] Pickford | Early Miocene grassland ecosystem at Bukwa, Mount Elgon, Uganda[END_REF][START_REF] Pickford | Early Pliocene Tragulidae and peafowls in the Rift Valley, Kenya: evidence for rainforest in East Africa[END_REF] and Kisingiri Volcano (Kenyan portion of Lake Victoria; [START_REF] Bestland | Volcanically influenced calcareous palaeosols from the Miocene Kiahera Formation, Rusinga Island, Kenya[END_REF][START_REF] Collinson | Taphonomy of the early Miocene flora, Hiwegi Formation, Rusinga Island, Kenya[END_REF] the landscape is dominated by woodlands with small patches of rainforest. The main debate is the amount of grassland an indicator of seasonal aridity which seemed to exist based on palaeosoils and fauna (gastropods and vertebrates). [START_REF] Bestland | Volcanically influenced calcareous palaeosols from the Miocene Kiahera Formation, Rusinga Island, Kenya[END_REF] suggested that, based on palaeosoils, precipitation ranged from 550-750 mm/yr.

The middle Miocene climate experienced greater differences, most likely with alternating drier and wetter periods. In the Nyanza Rift, east of present day Lake Victoria, (Maboko Fm, around 15 Ma;[START_REF] Retallack | Paleosols and paleoenvironments of the middle Miocene, Maboko Formation, Kenya[END_REF] data on palaeosoils indicate dry environments, with precipitation ranging from 300-500 mm/yr. In the Kenyan Rift (Tugen Hills area), palaeobotanical data suggest relatively dry conditions around 13.3-12.0 Ma (Ngorora Fm, [START_REF] Rasmussen | Middle -late Miocene palaeoenvironments, palynological data and a fossil fish Lagerstatte from the Central Kenya Rift (East Africa)[END_REF], with grassy savannah around 12.6 Ma (Kaberso Fm; Jacobs and Deino, 1996;[START_REF] Jacobs | Estimation of low-latitude paleoclimates using fossil angiosperm leaves: examples from the Miocene Tugen Hills, Kenya[END_REF], followed by deciduous forests with precipitation from 955-1185 mm/yr, indicating more tropical conditions (rainforest; Jacobs and Kabuye, 1987). The main challenge is determining the local (e.g. topographic effect due to block tilting) or regional (dome-scale)

M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT

33

meaning of these drier and wetter events. Most authors agree that widespread aridification occurred from the early to middle Miocene in the East African Dome.

The late Miocene in the Kenyan Rift (eastern branch of the EARS) is characterised by a drier period followed by extreme humidification around 9.5 Ma (Samburu Hill -Suguta Valley;Sakai et al., 2010). In the Tugen Hills, the open vegetation structures in a climate with a pronounced dry season and precipitation of 490-610 mm/yr indicate that a drier period occurred around 9-10 Ma (Waril site; [START_REF] Jacobs | Estimation of low-latitude paleoclimates using fossil angiosperm leaves: examples from the Miocene Tugen Hills, Kenya[END_REF]. In the Tugen Hills in the late Miocene (Messinian), the presence of deciduous forest indicates more humid conditions (Kapturo site, 7.2-6.7 Ma, precipitation from 730-1020 mm/yr; [START_REF] Jacobs | Estimation of low-latitude paleoclimates using fossil angiosperm leaves: examples from the Miocene Tugen Hills, Kenya[END_REF] and wet lowland rainforests (Mpesida Fm, Ma; [START_REF] Kingston | Stratigraphy, age and environments of the late Miocene Mpesida Beds, Tugen Hills, Kenya[END_REF] or gallery forests similar to the modern Tana River (Mpesida Fm, 6.3 Ma;[START_REF] De Franceschi | Fossil wood from the upper Miocene Mpesida Beds at Cheparain (Baringo District, Kenya): Botanical affinities and palaeoenvironmental implications[END_REF]. The high lake levels around 7.2 Ma also indicate a humid period in the western branch of the EARS (Simon et al., 2017). In the Kenyan Rift (Tugen Hills), stable isotope analysis of herbivore teeth (Lukeino Fm;Roche et al., 2013) shows evidence of drier conditions around 6.1-5.8 Ma and wetter conditions around 5.7 and 5.3-4.5 Ma. This is in agreement with results from the Gulf of Aden (DSDP site 231; Bonnefille, 2010) that show maximum aridity around 5.9 Ma. The two humidity peaks characterized here around 11 ad 9.5-9 Ma in the Zambezi catchment might be related to the post 12 Ma and 9.5 Ma humidification identified in the Kenyan rift. The relative aridification around 10 Ma is in agreement with the drier even characterized by [START_REF] Jacobs | Estimation of low-latitude paleoclimates using fossil angiosperm leaves: examples from the Miocene Tugen Hills, Kenya[END_REF] in the Waril site.

Conclusion

(1) We have here developed an integrated method combining biostratigraphy, orbitostratigraphy and sequence stratigraphy in order to define a high resolution age model for the Zambezi Delta

M A N U S C R I P T A C C E P T E D

ACCEPTED MANUSCRIPT 34 and to discuss its main control parameters that are expected to be either climato-eustatic or tectonic.

• Although the biostratigraphic study was realised on cuttings, argues are strong for robust ages as information from calcareous nannofossils reinforced by planktonic foraminifera is almost constantly consistent. In addition, we coupled for the Neogene the biostratigraphy results with orbital stratigraphy (correlation of third order unconformities with Earth eccentricity cycles) using the calculated Earth orbital solution of Laskar.

• Three orders of sequences were defined: (1) seventeen third order sequences for Neogene times -Pl.0 to Pl.5 for the Pliocene-Pleistocene time span and M.1 to M.11 for the Miocene;

(2) eight second order sequences from Late Cretaceous to Present; (3) one first order cycle subdivided into three steps, (an aggradational to retrogradational period during the Late Cretaceous, a mainly aggradational one until the middle Eocene, and a third prograding one corresponding to the Zambezi Delta initiation).

(2) From this stratigraphic framework we discussed the tectonic or climato-eustatic controls of the second-order sequences. 2) calibration of the third-order sequence boundaries on Laskar's orbital solution (eccentricity; [START_REF] Laskar | La2010: a new orbital solution for the long-term motion of the Earth[END_REF] based on the assumption that a sea level fall must correspond to a major cooling and therefore to a decrease in eccentricity. [START_REF] Catuneanu | Towards the standardization of sequence stratigraphy[END_REF] EXXON [START_REF] Posamentier | Eustatic controls on clastic deposition II -sequence and systems tract models[END_REF]

MRS

Marine carbonate sedimentation Continental sedimentation

Marine siliciclastic sedimentation Maximum flooding surface

Major sequence boundaries Alkaline Kimberlitic

1) 2) 1, 2) 1) 1) 1) 1, 2) 1) 3) 4) 2) 5) 3, 4) 1) 4, 5, 6, 7) 2, 3) 3) 4) 2) 1) 7) 5, 6) 8) 8) 3) 4, 5) 6, 7)
Compilation of data from literature : A) : (1) [START_REF] Leinweber | The crustal structure of the Central Mozambique continental margin -Wide angle seismic, gravity and magnetic study in the Mozambique Channel, Eastern Africa[END_REF] (2) [START_REF] Konig | Advanced insights into magmatism and volcanism of the Mozambique Ridge and Mozambique Basin in the view of new potential field data[END_REF]3) Goodlad et al., 1982;(4) [START_REF] Leinweber | Is there continental crust underneath the northern Natal Valley and the Mozambique Coastal Plains[END_REF](5) Tikku et al., 2002;(6) Cochran, 1988;(7) Raillard,1990 ;(8) [START_REF] Plummer | Mesozoic tectono-stratigraphic evolution of the Seychelles microcontinent[END_REF].

B):

(1) Storey et al., 1995; (2) [START_REF] Mahoney | Cretaceous volcanic rocks of the south Tethyan suture zone, Pakistan: implications for the Réunion hotspot and Deccan traps[END_REF] Foraminifers biozones : Subtropical Biozones from [START_REF] Berggren | Geochronology times scales and global stratigraphic correlation[END_REF], [START_REF] Berggren | A revised tropical to subtropical paleogene planktonic foraminiferal zonation[END_REF], [START_REF] Gradstein | The geologic time scale 2012[END_REF] 4) [START_REF] Bestland | Volcanically influenced calcareous palaeosols from the Miocene Kiahera Formation, Rusinga Island, Kenya[END_REF] (5) [START_REF] Collinson | Taphonomy of the early Miocene flora, Hiwegi Formation, Rusinga Island, Kenya[END_REF][START_REF] Lafourcade | Etude géologique et géophysique de la marge continentale du sud Mozambique (17°S à 28[END_REF] δO¹ (Zachos et al., 2001;[START_REF] Friedrich | Evolution of middle to Late Cretaceous oceans -a 55 my record of Earth's temperature and carbon cycle[END_REF]

V V V V V V V

  calculated long-term orbital solutions at eccentricity time-resolution for Cenozoic times. (3) This pattern is different from the Pleistocene one characterized by climatically-enhanced orbital frequencies (40 kyr: Early Pleistocene, 100 kyr: Middle-Late Pleistocene).

  slide and photograph collections, atlases, special papers) originating from herbarium specimens

  of the different vegetation types. Nevertheless, consistency of the slight fluctuations observed in pollen assemblages leads to consider cavings as negligible.

•

  A second uplift of the South African Plateau from the Oligocene to the beginning of the Miocene. This long-wavelength deformation induced a progressive tilt of the Zambezi Margin and relief denudation, as indicated byAFTA (Belton and Raab, 2010; Emmel et al., tilted sedimentary deposits (Cheringoma Fm and Urrongas Fm in southern Mozambique)(Flores, 1973).

  sequences S6-S4) or, more recently, alternating deltaic plains and shelf deposits due to numerous marine floods (sequences S4-S1). The clinoforms have high amplitude reflectors that consist mainly of clayey siltstones. The base of the clinoforms (fondoform or bottomsets) shows a wide variety of facies, from gravitary deposits to hemipelagites. The gravitary deposits (Fig.5) are either reflectors of differing degrees of continuity (alternating continuous and discontinuous sub-chaotic reflectors -shallow turbidite lobes) or are chaotic (Mass Transport Complexes (MTC): slumps to debris flows). The most obvious and common features are mounded structures with large aggradational sandwaves and channels characteristic of reworking and transport by oceanic currents (contourites s.l. ; e.g.Faugères et al., 1999; Rebesco et al., 2014 -Fig. 5) .

••

  The sequence boundary of sequence S8 was dated from planktonic foraminifera to the boundary between the Dicarinella asymetrica and Globotruncanita elevata calcarata biozones (well X2), and to that between Globotruncanita elevata calcarata and Dicarinella concavata on X1; i.e. around the Santonian-Campanian boundary.• The sequence boundary of sequence S7 (Upper Grudja Fm) is dated on the well X3 by both planktonic foraminifera and calcareous nannofossils between biozones UC16 (72-76 Ma, late Campanian) and NP4 (61.5-63.2 Ma, uppermost Danian) (calcareous nannofossils) and between Gansserina Gansseri (71.8-72.8 Ma, uppermost Campanian-base Maastrichtian) and P3a (61.2-62.2 Ma, uppermost Danian -base Selandian) zones (planktonic foraminifera). On the wells X2 and X1 it is only dated by planktonic foraminifera between Abathomphalus Mayaroenis (77.8-67.3 Ma, uppermost Campanian most of the Maastrichtian) and P3-P3a (62.2-60.7, Selandian) biozones (well X2), and between Gansserina gansseri and E5-P4c biozones (well X1). The uppermost Maastrichtian and the early Danian are missing, and no downward onlapping wedges that might be the early Danian missing in well X3 were identified from seismic lines. The early Danian seems a hiatus at the scale of the domain studied. The sequence boundary of sequence S6 (Cheringoma Fm) is dated on wells X1 and X3 by both planktonic foraminifera and calcareous nannofossils between zones P5 and E3-E2 (X3), and E5-P4c and E7b (well X1) (planktonic foraminifera) and between zones NP9 and NP10 (well X3) and NP12-NP8 and NP15-NP14 (well X1) (calcareous nannofossils). In the well X2 the sequence boundary is only dated by planktonic foraminifera between P5-E2 and E4-the age of the oldest underlying formation belongs to the foraminifer zone P4c and the one of the oldest overlying formation refers to biozone E7b.

  5 (base S2sequence boundary) at 5.8 Ma, Pl.4 at 5.0 Ma, Pl.3 at 3.8 Ma, Pl.2 (base S1 sequence boundary) at 3.0 Ma, Pl.1 at 1.0 Ma, Pl.0 at 0.2 Ma.4.3. Palaeoprecipitation evolution(Fig. 11, Supplementary materials) diagrams of wells X1 and X3 (Fig.11) show that the distribution of each pollen group is quite uniform during the late Oligocene as from the late Miocene up to mid-Pleistocene. The late Paleogene to middle Pleistocene pollen flora of the Zambezi catchment is dominated by Poaceae representing open vegetation and Cyperaceae representing freshwater ecosystems, supporting a uniform permanent contrast between two environments, the dry tropical domain and the flat humid habitat (swamps to little lakes). Few littoral plants (halophytes, mangrove elements, components of the tropical rain forest and warm-temperate and pioneer forests) were recorded. This might be somewhat biased by the course of the Zambezi River that only crossed these domains at its end. On the whole, the pollen assemblages preserved in the sediments offshore of the Zambezi Delta denote almost continuous warm and dry climatic conditions.

  isotope curves of global deep ocean water compiled by[START_REF] Friedrich | Evolution of middle to Late Cretaceous oceans -a 55 my record of Earth's temperature and carbon cycle[END_REF] andZachos et al. (2001) as proxies of climate-induced eustasy for the Cretaceous and Cenozoic, respectively.

  that induced the major uplift phase of the South African Plateau. The uplift began around the Cenomanian-Turonian boundary (around 94 Ma) and ended in the Campanian (80-75 Ma)[START_REF] Braun | Rapid erosion of the Southern African Plateau as it climbs over a mantle superswell[END_REF]. A possible cause of this unconformity by uplift is reinforced by the thermochronological data, which indicate a major cooling event of the rocks on both sides of the Zambezi outlet: the southern portion of the Zimbabwe Plateau(Belton and Raab, 2010) to the west and the southern North Mozambique to the east(Emmel et al., 2011).

  identified on both stratigraphic and geomorphological evidences a continuous second uplift phase of the southern African Plateau from 40 Ma (early Bartonian) to 20 Ma (end of Burdigalian) with an unconformity at 26 Ma (Chattian) that may be the paroxysm of this uplift. We relate the unconformity, approximately of the same age given uncertainties in dating microfossils from cuttings, to this second uplift of the South African Plateau and the associated rejuvenation of the Zambezi the siliciclastic supply and thus the formation of the modern Zambezi Delta.• S4 sequence boundary (late Chattian, 25-23 Ma) is related to the 26 Ma unconformity that[START_REF] Baby | Uplift history of a transform margin revealed by the stratigraphic record: The case of the Agulhas transform margin along the Southern African Plateau[END_REF] identified in the Durban Basin and interpreted as the paroxysmal period of the second phase of the South African Plateau uplift.

  et al., 2006) at that time a lowland setting indicate warm, humid conditions

  . The offshore drilling record (ODP Site 1085) for the late Miocene indicates at least two phases of aridification: (1) a progressive change (Dupont et al., 2011) from 10-6 Ma (late Miocene), with the development of semi-arid succulent vegetation corresponding to modern Cape flora (i.e.fynbos), and (2) a second phase at 4.3 Ma (early Pliocene;[START_REF] Hoetzel | Steps in the intensification of Benguela upwelling over the Walvis Ridge during Miocene and Pliocene[END_REF]. The early to middle Miocene aridification trend seems due to regional changes in southern Africa. The late be the first time that climate change differed between the Atlantic and Indian coasts of the southern African margins, with pervasive arid conditions in Namibia but a rapid return to more humid conditions in the Zambezi catchment.

•

  Figures and supplementary materials

Figures

  Figures

Fig. 1 :

 1 Fig. 1: The Zambezi sedimentary system. A: Location in Austral Africa (catchment) and

Fig. 2 :

 2 Fig. 2: Summary chart of approaches used to interpret seismic stratigraphy.

Fig. 3 :

 3 Fig. 3: Present day vegetation distribution within the Zambezi catchment (Timberlake,

Fig. 4 :

 4 Fig. 4: Summary chart of the main geodynamic (oceanic accretion, plumes, volcanism)

Fig. 5 :

 5 Fig. 5: Margin delta depositional profile: environments and lithology, clinoforms height

Fig. 6 :

 6 Fig. 6: Zambezi Delta regional seismic line from the upstream coastal plain bordered by

Fig. 7 :

 7 Fig. 7: Studied wells (see location on Fig. 1B): lithology from well-logs and cuttings,

Fig. 8 :

 8 Fig. 8: Biostratigraphy of Well X1. The grey stripes show the proposed correlations of the

Fig. 9 :

 9 Fig. 9: Biostratigraphy of Well X3. The grey stripes show the proposed correlations of the

Fig. 10 :

 10 Fig. 10: Age model for Zambezi Delta Neogene sediments: (1) repetitive unconformity-

Fig. 11 :

 11 Fig. 11: Reconstructed precipitation estimates of the Zambezi catchment from the

  1B for location) based on pollen records (this study see text for discussion) and comparison with the reference DSDP Site 231 (Gulf of Aden; Bonnefille, 2010); (2) compilation of the from scattered outcrops in East Africa mainly based on palaeobotanical data (woods, leaves, pollen grains), (3) regional (Mozambique Channel) and world-scale climatic data. The Mozambique Channel data (unpublished at the moment) were acquired in the frame of the PAMELA Project through a collaboration between geoscientists of Rennes University and palynologists of TOTAL Company (N. Buratti and D. Michoux).

Fig. 12 :

 12 Fig. 12: Summary chart of the stratigraphic data and their possible causes, deformations

  Figure2

  Figure4

  Figure7

  FIGURE 9

  Figure11



  Figure12

  The age of the oldest underlying formation refers to zones O1-2 and the one oldest overlying formation to zone M1. The minimum age range of the sequence boundary S4 is between 30.2 and 34 Ma and the maximum between 25.2 and 21.7 Ma, i.e. from Rupelian to most of the Aquitanian. The hiatus in well X2 is quite long (i.e. Rupelian to Aquitanian). Therefore we suggest to use the well X1 where no hiatus is observed. Based on X1, the sequence boundary S4 is posterior to the O6 biozone (27-25.2 Ma), a late Chattian age (25-23 Ma) is most probable.

This work was supported by the petroleum company TOTAL and the French oceanographic research agency IFREMER in the frame of the project PAMELA (Passive Margin Exploration Laboratory). All the data (seismic lines, well-logs and cuttings) were provided by TOTAL. We thank our colleagues of the PAMELA project for stimulating discussions. We also thank Brendan Simon for very helpful comments of the seismic interpretations.

We are very grateful to Marina Rabineau and to an anonymous reviewer for their critical comments that improved the early version of the manuscript.

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Zambezi system limits