Cédric Bougeault

Pierre Pellenard

Jean-François Deconinck

Stephen P Hesselbo

Jean-Louis Dommergues

Ludovic Bruneau

Théophile Cocquerez

Rémi Laffont

Emilia Huret

Nicolas Thibault

Jean- Louis Dommergues

Climatic and palaeoceanographic changes during the Pliensbachian (Early

Keywords: Early Jurassic, Pliensbachian, runoff, clay minerals, stable isotope, glacio-eustasy

Introduction

The Early Jurassic was a period of major environmental and biological changes contemporaneous with the break-up of Pangaea and intense volcanic phases linked to the CAMP (Central Atlantic Magmatic Province) and the Karoo-Ferrar large igneous provinces [START_REF] Little | Early Jurassic mass extinction: A global long-term event[END_REF][START_REF] Wignall | Large igneous provinces and mass extinctions[END_REF][START_REF] Wignall | The timing of paleoenvironmental change and cause-and-effect relationships during the Early Jurassic mass extinction in Europe[END_REF][START_REF] Jourdan | The 40 Ar/ 39 Ar ages of the sill complex of the Karoo large igneous province: Implications for the Pliensbachian-Toarcian climate change[END_REF][START_REF] Schaltegger | Precise U-Pb age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian post-extinction recovery[END_REF]Dera et al., 2011a;[START_REF] Guex | Thermal erosion of cratonic lithosphere as a potential trigger for mass-extinction[END_REF]. During the Early Toarcian, prominent organic matter (OM) accumulations in marine sediments, associated with anoxic conditions, were recorded in many parts of the world, defining the well-known and extensively studied Toarcian Oceanic Anoxic Event (T-OAE). A remarkable positive shift of the d 13 C values was triggered by OM storage in oceanic sediments [START_REF] Jenkyns | The early Toarcian (Jurassic) anoxic event: stratigraphic, sedimentary, and geochemical evidence[END_REF][START_REF] Jenkyns | Geochemistry of oceanic anoxic events[END_REF][START_REF] Al-Suwaidi | First record of the Early Toarcian Oceanic Anoxic Event from the Southern Hemisphere, Neuquén Basin, Argentina[END_REF][START_REF] Suan | Polar record of Early Jurassic massive carbon injection[END_REF][START_REF] Izumi | Early Toarcian (Early Jurassic) oceanic anoxic event recorded in the shelf deposits in the northwestern Panthalassa: Evidence from the Nishinakayama Formation in the Toyora area, west Japan[END_REF][START_REF] Krencker | The middle Toarcian cold snap: Trigger of mass extinction and carbonate factory demise[END_REF]. Within this positive carbon isotope excursion a strong negative carbon isotopic excursion (CIE) of -7‰ in average amplitude has been recognised in terrestrial organic matter and in marine sediments (Hesselbo et al., 2000a;[START_REF] Schouten | Effects of an oceanic anoxic event on the stable carbon isotopic composition of early Toarcian carbon[END_REF][START_REF] Kemp | Astronomical pacing of methane release in the Early Jurassic period[END_REF][START_REF] Van De Schootbrugge | Early Jurassic climate change and the radiation of organic-walled phytoplankton in the Tethys Ocean[END_REF][START_REF] Hesselbo | Carbon-isotope record of the Early Jurassic (Toarcian) Oceanic Anoxic Event from fossil wood and marine carbonate (Lusitanian Basin, Portugal)[END_REF][START_REF] Hesselbo | Stepwise atmospheric carbon-isotope excursion during the Toarcian Oceanic Anoxic Event (Early Jurassic, Polish Basin)[END_REF]. Intense volcanic activity from the Karoo-Ferrar magmatic province coupled with an increase of runoff conditions and temperature triggering oceanic methane injection and consequently light carbon release is a prominent suggestion to explain this negative excursion (Hesselbo et al., 2000a;[START_REF] Hesselbo | Carbon-isotope record of the Early Jurassic (Toarcian) Oceanic Anoxic Event from fossil wood and marine carbonate (Lusitanian Basin, Portugal)[END_REF][START_REF] Suan | Polar record of Early Jurassic massive carbon injection[END_REF][START_REF] Hermoso | Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to the middle Toarcian in the Paris Basin[END_REF]. New data from the Pliensbachian interval show that two other excursions in the d 13 C biogenic carbonate and organic matter content occurred: 1) a negative excursion (-2‰) at the Sinemurian-Pliensbachian boundary, namely the Sinemurian-Pliensbachian Boundary Event (SPBE) 2) a positive excursion (+2‰) during the Late Pliensbachian corresponding to the Late Pliensbachian Event [START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF][START_REF] Silva | Update of the carbon and oxygen isotopic records of the Early-Late Pliensbachian (Early Jurassic, ~187 Ma): Insights from the organic-rich hemipelagic series of the Lusitanian Basin (Portugal)[END_REF][START_REF] Franceschi | Early Pliensbachian (Early Jurassic) C-isotope perturbation and the diffusion of the Lithiotis Fauna: insights from the western Tethys[END_REF][START_REF] Silva | Organic matter production and preservation in the Lusitanian Basin (Portugal) and Pliensbachian climatic hot snaps[END_REF][START_REF] Gómez | Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)[END_REF]Peti et al., submitted). Most of these events are coeval with variations of seawater temperatures calculated from d 18 O values of bulk carbonate and calcified organisms. Warm periods occurred during the Late Sinemurian and the Early-Late Pliensbachian transition (e.g. Ibex to early Margaritatus Zones; [START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF][START_REF] Silva | Organic matter production and preservation in the Lusitanian Basin (Portugal) and Pliensbachian climatic hot snaps[END_REF][START_REF] Martinez | Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic[END_REF][START_REF] Gómez | Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)[END_REF], while a cooler phase was recognised during the Late Pliensbachian mainly on the basis of d 18 O data measured from belemnite rostra [START_REF] Rosales | Paleotemperature variations of Early Jurassic seawater recorded in geochemical trends of belemnites from the Basque-Cantabrian basin, northern Spain[END_REF]Dera et al., 2009b;[START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF][START_REF] Martinez | Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic[END_REF][START_REF] Gómez | Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)[END_REF], brachiopods and bivalves shells [START_REF] Suan | Secular environmental precursors to Early Toarcian (Jurassic) extreme climate changes[END_REF][START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF] and from sedimentological and palynological evidences [START_REF] Price | The evidence and implications of polar ice during the Mesozoic[END_REF][START_REF] Suan | Polar record of Early Jurassic massive carbon injection[END_REF]. Together with available d 13 C and d 18 O data, clay minerals could be used as an informative palaeoclimatic proxy, especially to better constrain continental weathering and humidity/aridity variations [START_REF] Robert | Antarctic subtropical humid episode at the Paleocene-Eocene boundary: Clay-mineral evidence[END_REF][START_REF] Vanderaveroet | A record of glacial/interglacial alternations in Pleistocene sediments off New Jersey expressed by clay mineral, grain-size and magnetic susceptibility data[END_REF][START_REF] Ruffell | Comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the Mesozoic of NW Europe[END_REF][START_REF] Pellenard | Carbon cycle and sea-water palaeotemperature evolution at the Middle-Late Jurassic transition, eastern Paris Basin (France)[END_REF]. The kaolinite/illite ratio is considered to be a reliable proxy of humid conditions during the Jurassic [START_REF] Chamley | Clay Sedimentology[END_REF][START_REF] Hallam | Palaeoclimatic significance of changes in clay mineralogy across the Jurassic-Cretaceous in England and France[END_REF][START_REF] Pellenard | Mineralogical variability of Callovo-Oxfordian clays from the Paris Basin and the Subalpine Basin[END_REF][START_REF] Raucsik | Climato-environmental controls on clay mineralogy of the Hettangian-Bajocian successions of the Mecsek Mountains, Hungary: An evidence for extreme continental weathering during the early Toarcian oceanic anoxic event[END_REF]Dera et al., 2009a;[START_REF] Hesselbo | Late Jurassic palaeoclimatic change from clay mineralogy and gamma-ray spectrometry of the Kimmeridge Clay, Dorset, UK[END_REF][START_REF] Hermoso | Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to the middle Toarcian in the Paris Basin[END_REF][START_REF] Pellenard | Carbon cycle and sea-water palaeotemperature evolution at the Middle-Late Jurassic transition, eastern Paris Basin (France)[END_REF]. Kaolinite contents have been used to build long-term palaeohumidity curves for the Pliensbachian-Toarcian interval (Dera et al., 2009a). At the scale of the Tethyan domain, global enrichments of kaolinite during the Davoei Zone and during the early Toarcian (Falciferum to Bifrons Zones) were interpreted as periods of enhanced runoff on landmasses, while decreasing proportions of this mineral during the late Pliensbachian, suggested a colder and drier period, in agreement with the d 18 O fluctuations (Dera et al., 2009a(Dera et al., , 2009b(Dera et al., , 2011a;;[START_REF] Martinez | Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic[END_REF][START_REF] Gómez | Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)[END_REF]. In more detail, a significant and brief increase of kaolinite was also identified at the base of the Serpentinum Zone, synchronous with the negative shifts in carbon isotopes (d 13 C org and d 13 C carb ), and associated with an increase of temperature measured from the d 18 O bulk carbonate [START_REF] Hermoso | Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to the middle Toarcian in the Paris Basin[END_REF]. Again, the enrichment of kaolinite supports enhanced runoff and continental weathering during a brief warming episode and the reliability of clay minerals as sensitive climate proxies.

Despite these relationships between clay mineralogy and geochemical proxies in the late

Pliensbachian and Toarcian, links between d 13 C disruption, sea temperature change, and kaolinite enrichment still remain poorly described in the remaining Lower Jurassic. In the present study, we cover the entire Pliensbachian stage through a high-resolution analysis of clay mineralogy and carbon and oxygen isotopes in multiple sections from the NW European

Geological setting

During the Early Jurassic, the NW Tethyan domain corresponded to the extension of the Tethys Ocean which was characterised by an archipelago, composed of large islands inherited from the Variscan orogeny surrounded by epicontinental seas [START_REF] Thierry | Late Sinemurian[END_REF]. The NW Tethyan domain was also connected to the Arctic Sea and the Panthalassa Ocean through the Viking and Hispanic corridors implying different water mass influences (Dera et al., 2009b). This domain is generally subdivided into two parts, with the Mediterranean area, and a NW European domain that includes the Paris and the Wessex basins where boreholes and sections analysed in this study are located (Fig. 1).

The Paris Basin is an intracratonic basin surrounded by four landmasses, namely the London-Brabant Massif to the north, the Armorican Massif to the west, the Central Massif to the south and the Bohemian Massif to the east. Located in the southern part of the Paris Basin, to the north of the Central Massif, the Sancerre borehole (Callovian to Carboniferous) was drilled during the "Géologie Profonde de la France" programme (Deep Geology of France, [START_REF] Lorenz | Forage scientifique de Sancerre-Couy (Cher)[END_REF]. From the end of the Sinemurian to the Lower Pliensbachian, sediments are dominantly clayey limestone, while the Upper Pliensbachian is marked by claystone. The Pliensbachian-Toarcian boundary is characterised by some limestone beds. The Lower Toarcian strata comprise marl and organic-rich shale beds. Previous mineralogical and geochemical investigations were performed by [START_REF] Delavenna | Influence des cycles eustatiques et de la tectonique synsédimentaire sur la minéralogie du Lias et du Dogger du forage de Sancerre-Couy (Cher). Programme Géologie profonde de la France[END_REF], [START_REF] Hermoso | Expression of the Early Toarcian negative carbon-isotope excursion in separated carbonate microfractions (Jurassic, Paris Basin)[END_REF][START_REF] Hermoso | Dynamics of a stepped carbon-isotope excursion: Ultra high-resolution study of Early Toarcian environmental change[END_REF][START_REF] Hermoso | Black shale deposition during Toarcian supergreenhouse driven by sea level[END_REF] and [START_REF] Hermoso | Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to the middle Toarcian in the Paris Basin[END_REF]. From this core, 283 samples were analysed by X-ray diffraction.

The Montcornet borehole (A901 site) is located close to the Ardennes Massif in the northern part of the Paris Basin. Reaching 1100 metres in depth, it was drilled by Andra (the French National Radioactive Waste Management Agency) from Turonian chalks to the Devonian basement. The Lower Pliensbachian is composed of marl and limestone beds with pyritised burrows and phosphate nodules in the upper part. The Upper Pliensbachian comprises marl and claystone with some diagenetic siderite-rich nodules and thin accumulations of bivalve shells interpreted as tempestites. The Pliensbachian-Toarcian boundary is poorly defined biostratigraphically, but likely corresponds to the occurrence of limestone beds, coeval with the "Grès Médioliasiques" Fm, recognised in the rest of the Paris Basin and interpreted as a regressive facies [START_REF] Brigaud | Growth and demise of the Jurassic carbonate platform in the intracratonic Paris Basin (France): Interplay of climate change, eustasy and tectonics[END_REF]. The Toarcian is characterised by locally organic-rich and laminated shale. An abundant fauna including nektonic (ammonites and belemnites) and benthic organisms (bivalves, brachiopods, crinoids) occurs throughout the core. Previous analyses have been performed on biostratigraphy, magnetostratigraphy [START_REF] Yang | Hettangian and Sinemurian magnetostratigraphy from Paris Basin[END_REF][START_REF] Moreau | Pliensbachian magnetostratigraphy: new data from Paris Basin (France)[END_REF] and mineralogy [START_REF] Debrabant | Clay sedimentology, mineralogy and chemistry of Mesozoic sediments drilled in the northern Paris Basin[END_REF]. 197 samples have been analysed for clay mineralogy and 213 samples for isotope geochemistry. In addition, 50 new specimens of ammonites have been collected to help refine the biostratigraphy.

Additional clay mineral data from two sections (Corbigny, South Paris Basin, France and Charmouth, Wessex Basin, U.K) have been used for further comparisons (Fig. 1).

Materials and methods

Clay mineralogy

A total of 480 samples have been analysed using X-Ray Diffraction (XRD). After a gentle crush, powdered samples were decarbonated with a 0.2M HCl solution. The fraction below two microns (clay sized particles), was extracted with a syringe after decantation of the suspension during 1h35 following the Stokes law, and then centrifuged. Ammonia water was added to samples from Sancerre to help their deflocculation as recommended by [START_REF] Holtzapffel | Les minéraux argileux: préparation, analyse diffractométrique et détermination[END_REF]. Clay residue was then smeared on oriented glass slides and run in a Brucker D4 Endeavour diffractometer with CuKα radiations, LynxEye detector and Ni filter under 40 kV voltage and 25 mA intensity (Biogeosciences laboratory, University of Burgundy). Scanning from the goniometer ranges from 2.5° to 28° for each analysis. Three runs were performed for each sample to discriminate clay phases: 1) Air-drying; 2) Ethylene-glycol solvation; 3) Heating at 490°C, as recommended by [START_REF] Moore | X-Ray Diffraction and the Identification and Analysis of 679 Clay Minerals[END_REF]. Clay minerals were identified using their main diffraction (d 001 ) peak and by comparing the three diffractograms obtained. Clay minerals identified are the following: R0 type illite-smectite mixed-layer (17 Å based on glycolated run condition) referred to smectite for the following sections; R1 type illite-smectite mixed-layer (around 11.5 Å on air-drying conditions and 13 Å after ethylene-glycol solvation); chlorite (14.2 Å, 7.1 Å, 4.7 Å and 3.54 Å peaks); illite (10 Å, 5 Å, 3.33 Å); kaolinite (7.18 Å and 3.58 Å peaks). Estimated proportions of each clay mineral were performed using the MacDiff 4.2.5 software [START_REF] Petschick | MacDiff 4.2.2[END_REF] on glycolated diffractograms. As the main (d 001 ) peak of kaolinite and the (d 002 ) peak of chlorite are overlapping, a deconvolution procedure was applied on the (d 004 ) peak area of chlorite (3.54 Å) and (d 002 ) peak area of kaolinite (3.57 Å) to estimate properly both minerals proportions using the 7.1 peak (d 001kaolinite + d 002chlorite ). Chlorite percentage was calculated using the mean between (d 001 ) and (d 002 ) chlorite peak areas considering that chemical nature in chlorite impact the (d 001 )/(d 002 ) ratio [START_REF] Moore | X-Ray Diffraction and the Identification and Analysis of 679 Clay Minerals[END_REF]. The K/I ratio based on (d 001 ) peak area of each minerals was systematically calculated.

Scanning Electronic Microscope (SEM) observations were performed with a JEOL JSM 6400F Field Emission SEM (ARCEN platform of the LICB laboratory of the University of Burgundy).

Geochemical analyses

Isotope analyses on bulk carbonate oxygen and carbon (d 18 O Carb and d 13 C Carb ) were performed using a carbonate preparation device Kiel IV coupled with a Delta V Plus mass spectrometer (ThermoFisher) at the Biogeosciences laboratory (University of Burgundy). 130-900µg of rock were cleaned with ethanol, finely powdered and dried at 50°C for 12 hours in a stove. Carbonates were reacted with purified orthophosphoric acid at 70°C. Samples were calibrated to V-PDB using NBS-19. Replicates were regularly made to evaluate reproducibility which are respectively of 0.04‰ and 0.08‰ for d 13 C Carb and d 18 O Carb .

Statistical analyses

The SiZer analysis (Significance of Zero crossings of smoothed estimates e.g. [START_REF] Marron | When is a feature really there? The SiZer approach[END_REF] was used on the K/I ratio to define significant changes in kaolinite content. This method consists on the analysis of the derivative of a smoothed curve obtained from a kernel type regression using different levels of smoothing (noted h). SiZer method compiles derivative curves with their 95% confidence intervals. The morphology of the curves is analysed on the second derivative to identify wide patterns (bulge, hollow) and short patterns (peak) suggested from the biostratigraphic framework. Results are presented on a SiZer map indicating significant changes in the curve morphology of the investigated parameter. The abscissa characterises the level of smoothing (window size h in log scale) and the ordinate the depth. Long amplitude changes in the K/I ratio are detected on large window analysis (i.e. h = log (1)), whereas short amplitude changes are detected on short window analysis (i.e. h = log (0)). Bulges are shown in red, hollows in blue. Grey surfaces are interpreted as not statistically significant.

Results

Biostratigraphic framework

The biostratigraphic framework has been recently revised at Sancerre (see Peti et al., in press). At Montcornet, new investigations have been conducted to complete the study of [START_REF] Moreau | Pliensbachian magnetostratigraphy: new data from Paris Basin (France)[END_REF]. All ammonites chronozones are recognised in the Pliensbachian stage except the Spinatum Zone. Ammonites and biozonation boundaries are precisely reported on Fig. 2 and synthetically reported on Figs. 3 and4 (grey intervals are considered as intervals of uncertainties). The detail of identified ammonites and their biostratigraphic attribution are reported in the supplementary file (Suppl. Mat. Fig. 1).

Clay mineralogy

Sancerre borehole (South Paris Basin)

Clay mineral assemblages from the Sancerre borehole mainly comprise kaolinite (13-50%), illite (24-57%), R1 Type illite-smectite mixed-layer (IS R1; 13-29%) and chlorite (7-24%; Fig. 3). The main features are coeval variations between: 1) kaolinite and chlorite, and;

2) illite and IS R1. As a consequence, kaolinite and illite contents are inversely related, and these minerals also display the greatest variations, which exceed 20% throughout the series.

Therefore, the K/I ratio can be used as a reliable proxy of mineralogical changes. Based on the K/I ratio and the associated SiZer map, two major changes are observed during: 1) the Davoei Zone (Lower Pliensbachian; interval Ⓐ on Fig. 3), and; 2) the Spinatum Zone (Late Pliensbachian; interval Ⓑ on Fig. 3). Minor changes are visible: 1) around the Sinemurian-Pliensbachian boundary (interval ① on Fig. 3), and; 2) during the Margaritatus Zone, where three cycles are observed within the Stokesi (interval ② on Fig. 3) Subnodosus (interval ③ on Fig. 3) and Gibbosus (interval ④ on Fig. 3) Subzones. Both major and minor changes of the K/I ratio are observed with the SiZer analysis that statistically validate their occurrence.

Montcornet borehole (North Paris Basin)

Similar clay mineral assemblages are recognised at Montcornet, including kaolinite (2-54%), illite (9-58%), IS R1 (0-19 %), and chlorite (5-31%; Fig. 4). Two intervals showing smectite (up to 78%) are however identified during the Ibex Zone (interval ① on Figure 4) and before and during the "Grès Médioliasiques" Fm (interval ② on Fig. 4). The K/I ratio shows three major changes during the Pliensbachian: 1) around the Ibex-Davoei transition (interval Ⓐ on Fig. 4); 2) after the Margaritatus Zone (interval Ⓑ on Fig. 4), and; 3) during the "Grès Médioliasiques" Fm (interval Ⓒ on Fig. 4). The first two changes in the K/I ratio are validated by the SiZer analysis. The net and brief increase of the K/I ratio during the "Grès Médioliasiques" is associated to a marked lithological change expressed by the appearance of bioclastic limestones with reworked mud clasts (772.4-776.8 m), characteristic of more proximal and high-energy facies (Fig. 2). SEM observations have been performed on one bioclastic limestone bed (772.75 m) and reveal typical authigenic vermiform kaolinite in the porosity (Fig. 5 A-C). Comparison has been made with one kaolinite-rich sample from claystone at 812 m, considered as representative of detrital clayey sediments, where only typical detrital shapes for clay particles have been observed, associated with rare calcitic bioclasts and framboidal pyrite (Fig. 5 D). (Corbigny, South Paris Basin; Charmouth, Wessex Basin) Computed K/I ratio from clay mineralogy data of the Corbigny section (see [START_REF] Dera | Le rôle des changements paléoclimatiques sur l'évolution de la biodiversité au Pliensbachien et au Toarcien[END_REF] shows low values during the Jamesoni and Ibex Zones and an increase during the Davoei Zone (Fig. 6). In the Charmouth section, a low K/I ratio is also registered during the Jamesoni Zone, while a slight increase starts in the Ibex Zone (Fig. 6). No data are currently available above this level.

Additional sections

Carbon and oxygen isotope geochemistry (Montcornet borehole)

The bulk carbonate carbon isotope (d 13 C carb ) signal recorded through the Pliensbachian shows several significant changes (Fig. 3). A negative excursion of at least 1‰ (from 1.1‰ to and increase to 1.6‰ upward. From 766m, a net decrease of values is marked by two steps with the first one going down to 0‰ and the second one to -4‰.

The d 18 O carb signal recorded from the bulk carbonate of Montcornet shows more scattered values, yet some trends are observed and detailed in the supplementary material (Suppl. Mat. Fig. 2). Values range from -6.8 to -1.7‰. No covariation is visible between carbon and oxygen isotope data.

Discussion

Influence of diagenesis

Clay mineral diagenesis

Lower Jurassic deposits from the Paris Basin are recognised to have sustained a low to moderate burial diagenesis as shown by apatite fission tracks indicating a burial temperature slightly greater than 60°C [START_REF] Blaise | Reconstruction of low burial (<100 °C) in sedimentary basins: a comparison of geothermometer in the intracontinental Paris Basin[END_REF].

At Montcornet, several lines of evidence including the occurrence of R0 type illitesmectite mixed-layer (IS R0) in two intervals and mean T max values below 430°C indicating immature organic matter [START_REF] Disnar | Sédimentation de la matière organique dans le nord-est du Bassin de Paris: conséquences sur le dépôt des argilites carbonées du Toarcien inférieur[END_REF], confirm a weak influence of thermal diagenesis linked to burial. IS R0 are known to be particularly sensitive to burial diagenesis and transform into IS R1 by illitisation processes with temperatures over 60-70°C [START_REF] Merriman | Patterns of very low-grade metamorphism in metapelitic rocks[END_REF][START_REF] Lanson | Diagenetic smectite-to-illite transition in clay-rich sediments: a reappraisal of X-ray diffraction results using the multispecimen method[END_REF][START_REF] Środoń | K-Ar dating of the Lower Palaeozoic K-bentonites from the Baltic Basin and the Baltic Shield: implications for the role of temperature and time in the illitization of smectite[END_REF][START_REF] Dellisanti | Use of T max as a thermal maturity indicator in orogenic successions and comparison with clay mineral evolution[END_REF].

In the Sancerre borehole, the influence of burial diagenesis on clay assemblages is more questionable as IS R0 have not been identified. These minerals were either absent during sedimentation or have been transformed through incipient illitisation processes. However, mean Tmax values below 435°C indicate also an organic matter immaturity in the south of the Paris Basin [START_REF] Hermoso | Dynamics of a stepped carbon-isotope excursion: Ultra high-resolution study of Early Toarcian environmental change[END_REF]. Consequently, as the occurrence of IS R0 is consistent with such T max values [START_REF] Dellisanti | Use of T max as a thermal maturity indicator in orogenic successions and comparison with clay mineral evolution[END_REF], these minerals were likely absent during sedimentation.

The kaolinite/illite ratio decreases with depth in all investigated sites (Figs. 3,4 and6).

This observation could raise the question of a potential illitisation of kaolinite associated to burial diagenesis [START_REF] Ruffell | Comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the Mesozoic of NW Europe[END_REF][START_REF] Worden | Clay minerals in sandstones: controls on formation, distribution and evolution[END_REF]. In such cases, illitisation of kaolinite with depth is generally progressive, while in the two studied boreholes the observed decrease of kaolinite is abrupt, rather indicating a palaeoenvironmental control. In addition, in the two boreholes, the main striking feature is the coeval decrease of the K/I ratio during the same ammonite biozone (i.e. Davoei Zone; Figs. 3 and4). If the decrease of kaolinite with depth had been triggered by burial diagenesis, alteration at the same a stratigraphic horizon in different locations would have been an unlikely outcome. We suggest therefore that in both boreholes the influence of burial diagenesis on the clay mineral assemblages is negligible.

The occurrence of authigenic kaolinite is open to discussion as it is commonly associated with porous rocks such as limestone and sandstone. This mineral grows in pore spaces during eo-and meso-diagenesis by flushing of meteoric waters [START_REF] Lanson | Authigenic kaolin and illitic minerals during burial diagenesis of sandstones: a review[END_REF][START_REF] Worden | Clay minerals in sandstones: controls on formation, distribution and evolution[END_REF]. In both boreholes, there is no obvious relationship between lithology and clay mineralogy (Figs. 3 and4). However, in a bioclastic limestone bed at 772.75 m in the Montcornet borehole, a high proportion of kaolinite (up to 55%) characterises the clay fraction (Figs. 2 and4). Scanning Electronic Microscopy (SEM) observations revealed typical authigenic vermiform kaolinite in this sample (Fig. 5 A-C), suggesting that a large part of kaolinite content from this bed is related to fluid circulation. Other SEM observations from clayey and limestone beds show common detrital shape morphologies, suggesting that kaolinite formed by authigenesis is restricted to only one porous interval (Fig. 5C).

Influence of diagenesis on the isotopic signal

The carbonate fraction of the Pliensbachian marl and claystone of the Montcornet borehole is a mixture of cemented micro-crystalline calcite (micrite) and thin bioclasts; these were avoided in the process of microsampling. Measured isotopic composition of calcite in bulk rocks ranges from -4.2 to 2.7 ‰ for the d 13 C and from -6.8to -1.7 ‰ for the d 18 O, and are consistent with values previously published from other Pliensbachian and Toarcian sections [START_REF] Jenkyns | Chemostratigraphy of the Jurassic System: applications, limitations and implications for palaeoceanography[END_REF][START_REF] Silva | Update of the carbon and oxygen isotopic records of the Early-Late Pliensbachian (Early Jurassic, ~187 Ma): Insights from the organic-rich hemipelagic series of the Lusitanian Basin (Portugal)[END_REF][START_REF] Léonide | Drowning of the carbonate platform as a precursor stage of the Early Toarcian global anoxic event (Southern Provence sub-Basin, South-east France)[END_REF][START_REF] Hermoso | Black shale deposition during Toarcian supergreenhouse driven by sea level[END_REF]Duarte et al., 2014). In Jurassic claystones, characterised by poor permeability and low burial temperatures, the primary carbon isotope signal is frequently well-preserved during early and late diagenetic processes (e.g. [START_REF] Hermoso | Expression of the Early Toarcian negative carbon-isotope excursion in separated carbonate microfractions (Jurassic, Paris Basin)[END_REF][START_REF] Lavastre | Water circulation control on carbonate-δ 18 O records in a low permeability clay formation and surrounding limestones: The Upper Dogger-Oxfordian sequence from the eastern Paris basin, France[END_REF][START_REF] Pellenard | Carbon cycle and sea-water palaeotemperature evolution at the Middle-Late Jurassic transition, eastern Paris Basin (France)[END_REF]. Similar coeval d 13 C carb fluctuations recognised in other Pliensbachian series well-dated by ammonites (e.g. [START_REF] Silva | Update of the carbon and oxygen isotopic records of the Early-Late Pliensbachian (Early Jurassic, ~187 Ma): Insights from the organic-rich hemipelagic series of the Lusitanian Basin (Portugal)[END_REF][START_REF] Duarte | Carbon isotope stratigraphy and ammonite biochronostratigraphy across the Sinemurian-Pliensbachian boundary in the western Iberian margin[END_REF] (base Ibex Zone) and 790 m and 775 m (Spinatum Zone?), which may suggest cooler temperatures during these two intervals. Nevertheless, bulk oxygen isotope data have to be used with caution here as they are much more sensitive to diagenetic effects than carbon isotope data [START_REF] Marshall | Climatic and oceanographic isotopic signals from the carbonate rock record and their preservation[END_REF][START_REF] Jenkyns | Chemostratigraphy of the Jurassic System: applications, limitations and implications for palaeoceanography[END_REF].

Significance of the clay mineral record

Clay mineral assemblages are composed of a mixture of illite, IS R1, occasional IS R0, kaolinite and chlorite, and this composition is a very common feature of Early Jurassic sediments from European basins [START_REF] Delavenna | Influence des cycles eustatiques et de la tectonique synsédimentaire sur la minéralogie du Lias et du Dogger du forage de Sancerre-Couy (Cher). Programme Géologie profonde de la France[END_REF][START_REF] Deconinck | Clay mineral assemblages of Mesozoic pelagic and flysch sediments of the Lombardian Basin (Southern Alps): implications for palaeotectonics, palaeoclimate and diagenesis[END_REF][START_REF] Debrabant | Clay sedimentology, mineralogy and chemistry of Mesozoic sediments drilled in the northern Paris Basin[END_REF][START_REF] Duarte | Clay minerals and geochemical evolution in the Toarcian-lower Aalenian of the Lusitanian Basin (Portugal)[END_REF][START_REF] Deconinck | Environmental controls on clay mineralogy of an Early Jurassic mudrock (Blue Lias Formation, southern England)[END_REF][START_REF] Jeans | Clay mineralogy of the Jurassic strata of the British Isles[END_REF][START_REF] Raucsik | Climato-environmental controls on clay mineralogy of the Hettangian-Bajocian successions of the Mecsek Mountains, Hungary: An evidence for extreme continental weathering during the early Toarcian oceanic anoxic event[END_REF]Dera et al., 2009a;[START_REF] Brański | The mineralogical record of the Early Toarcian stepwise climate changes and other environmental variations (Ciechocinek Formation, Polish Basin)[END_REF][START_REF] Lézin | Geochemical disturbance and paleoenvironmental changes during the Early Toarcian in NW Europe[END_REF][START_REF] Hermoso | Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to the middle Toarcian in the Paris Basin[END_REF].

These clay minerals are considered to be chiefly inherited from detrital sources, because burial diagenesis is low and authigenesis only observed in one porous interval. No evidence of major tectonic rejuvenation of landmasses is reported for the Pliensbachian in the Paris Basin, which is thought to have been broadly a quiescent period in an extensional subsidence context [START_REF] Brunet | Subsidence of the Paris Basin[END_REF][START_REF] Guillocheau | Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints[END_REF][START_REF] Beccaletto | Overview of the subsurface structural pattern of the Paris Basin (France): Insights from the reprocessing and interpretation of regional seismic lines[END_REF]. Consequently, clay mineral supplies were likely controlled by variations in eustasy, climate, and sediment source area.

Clay mineralogy is partly dependent on the nature of weathered rocks outcropping on emerged landmasses, where it may originate from either contemporaneous soils or old sediments. Although proximal continental areas were the main sources, more distal sources could also be expected, because clay minerals are transportable over long distances by marine or aeolian currents. The main landmasses surrounding the Paris and the Wessex basins were the London-Brabant Massif to the north prolonged by the Rhenish Massif eastward, the Bohemian Massif to the east, the Massif Central to the south prolonged by the Armorican Massif westward, the Cornubian-Welsh High and Irish Massif to the west and the Scottish Massif to the northwest (Figs. 1 and7). Erosion of these emerged lands, mainly composed of Palaeozoic igneous, metamorphic and sedimentary rocks, would have favoured inputs of primary clay minerals such as illite or chlorite. Weathering of the crystalline basement, may have also provided IS R1, smectite (IS R0) and kaolinite. This latter mineral may be reworked from the basement sedimentary rocks together with illite and chlorite [START_REF] Deconinck | Environmental controls on clay mineralogy of an Early Jurassic mudrock (Blue Lias Formation, southern England)[END_REF]Dera et al., 2009a).

Origin of smectite

Interestingly, smectite is only reported in the Montcornet borehole for the Ibex Zone and around the Pliensbachian-Toarcian transition. Differential sedimentation of clay minerals is responsible for the increase of kaolinite, commonly observed during regression phases in association with proximal facies, whereas smectite and mixed-layer minerals are more frequently recorded during associated with maximum flooding surfaces [START_REF] Chamley | Clay Sedimentology[END_REF][START_REF] Ruffell | Comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the Mesozoic of NW Europe[END_REF][START_REF] Pellenard | Mineralogical variability of Callovo-Oxfordian clays from the Paris Basin and the Subalpine Basin[END_REF][START_REF] Godet | Platform-induced clay-mineral fractionation along a northern Tethyan basin-platform transect: implications for the interpretation of Early Cretaceous climate change (Late Hauterivian-Early Aptian)[END_REF]. Inferred large-scale transgressive-regressive (T/R) facies cycles from European domains [START_REF] Hardenbol | Mesozoic and Cenozoic sequence chronostratigraphic framework of European basins[END_REF][START_REF] Jacquin | Major transgressive/regressive cycles: the stratigraphic signature of European basin development. Mesozoic and Cenozoic Sequence Stratigraphy of European basins[END_REF] are reproduced on Figures 3 and4. These so-called 'second-order' order T/R cycles (T4/R4, T5/R5) match well with the sedimentological pattern and depositional environments observed through the two boreholes, in particular for cycles defined in the Tethyan domains. A maximum flooding surface is reported within the lower Margaritatus Zone (Stokesi Subzone). Regressive maxima are at the top of the Ibex Zone for the Tethyan domains (or at the top of the Davoei Zone for the Boreal domains) and the top of the Spinatum Zone (Pliensbachian/Toarcian boundary). The Spinatum Zone was not recognised in the Montcornet borehole, but the bioclastic limestone beds between 772 and 777 m are attributed to an equivalent of the "Grès Médioliasiques Fm" well known throughout the Paris Basin, dated to the Spinatum Zone and corresponding to a regressive maxima [START_REF] Hermoso | Black shale deposition during Toarcian supergreenhouse driven by sea level[END_REF][START_REF] Brigaud | Growth and demise of the Jurassic carbonate platform in the intracratonic Paris Basin (France): Interplay of climate change, eustasy and tectonics[END_REF]. Surprisingly, these regressive maxima correspond to the two smectite-rich intervals with proportions reaching more than 50% (Fig. 4). Smectite was exclusively restricted to the northern part of the Paris Basin until the Late Jurassic [START_REF] Debrabant | Clay sedimentology, mineralogy and chemistry of Mesozoic sediments drilled in the northern Paris Basin[END_REF][START_REF] Pellenard | Mineralogical variability of Callovo-Oxfordian clays from the Paris Basin and the Subalpine Basin[END_REF], which suggests it likely originated from the London-Brabant and Rhenish massifs. Compared to other massifs inherited from the Variscan orogeny, the London-Brabant and Rhenish-Eiffel massifs including the Ardennaise platform should constitute moderate and flat relief during the Jurassic. This morphology was favourable to the formation of smectite-rich soils under semi-arid to temperate climates with strong seasonality [START_REF] Chamley | Clay Sedimentology[END_REF][START_REF] Paquet | Soils and Sediments, Mineralogy and Geochemistry[END_REF], whereas illite, chlorite and IS R1 could be formed on higher relief with steeper slopes and less pronounced weathering. A reported regional uplift with moderate average speed of unroofing of the London-Brabant and Rhenish-Eiffel massifs throughout the Jurassic (Vercoutere and Van den Haute, 1993) may also have played a role for denudation of relief and the peneplanation favourable for the storage of smectites. During regressive phases, the smectite-rich soils from low relief landmass and previously smectite-rich sediments stored on platforms were preferentially eroded, and are hypothesized to have supplied adjacent areas of the basin (Fig. 7A). By contrast, during sea-level highstand, flooding of the flat London-Brabant Massif prevented smectite-rich sedimentation in the Paris Basin (Fig. 7B). This uncommon relationship between smectite sedimentation and low sea-level is only observed in the north of the Paris Basin and the Boulonnais area from the Callovian to the Tithonian [START_REF] Schnyder | Stratigraphie et analyse sédimentologique du passage Oxfordien/Kimméridgien dans le Boulonnais[END_REF][START_REF] Pellenard | Mineralogical variability of Callovo-Oxfordian clays from the Paris Basin and the Subalpine Basin[END_REF][START_REF] Deconinck | Les dépôts du Kimméridgien et du Tithonien du nord-ouest du Bassin de Paris (Haute-Normandie, Boulonnais)[END_REF][START_REF] Hesselbo | Late Jurassic palaeoclimatic change from clay mineralogy and gamma-ray spectrometry of the Kimmeridge Clay, Dorset, UK[END_REF]. The present study shows that as early as the Pliensbachian, the London-Brabant Massif exhibited a flat morphology by comparison with other emerged landmasses.

Eustatic sea-level variations can thus explain here some regional clay mineralogical features, but is insufficient to explain the several kaolinite changes, correlated between the four studied sites.

Significance of the K/I ratio

The K/I ratio shows two main significant changes at the investigated localities: 1) a sharp increase at the transition between the Ibex and Davoei Zones, and; 2) a decrease in the Spinatum Zone (Fig. 6). The abrupt increase of the K/I ratio at the base of the Davoei Zone coincides with the onset of the T5 2 nd order transgressive cycle (Tethyan domains) and remains high up to the top of the R5 regressive cycle (Figs. 3 and4). Looking at large scale trends of K/I ratio in the Sancerre and Montcornet boreholes, regressive facies trends are not characterised by an increase of kaolinite but rather by a decrease (Ibex and Spinatum Zones), and no evidence linking kaolinite maxima and regressive maxima can be identified. Kaolinite variations and inferred K/I ratio are unlikely to be forced by a unique eustatic control.

Clay minerals are known to reflect climate through continental weathering and runoff in modern environments and in deep time [START_REF] Chamley | Clay Sedimentology[END_REF][START_REF] Hallam | Palaeoclimatic significance of changes in clay mineralogy across the Jurassic-Cretaceous in England and France[END_REF][START_REF] Paquet | Soils and Sediments, Mineralogy and Geochemistry[END_REF][START_REF] Thiry | Palaeoclimatic interpretation of clay minerals in marine deposits: an outlook from the continental origin[END_REF]Dera et al., 2009a). Kaolinite is preferentially formed at low latitudes under hot and wet tropical climate, allowing strong hydrolysing processes to take effect [START_REF] Paquet | Soils and Sediments, Mineralogy and Geochemistry[END_REF][START_REF] Thiry | Palaeoclimatic interpretation of clay minerals in marine deposits: an outlook from the continental origin[END_REF]. By contrast, chlorite and illite are formed in drier climates where physical erosion prevails [START_REF] Chamley | Clay Sedimentology[END_REF]. Therefore, many authors classically use kaolinite as a reliable indicator of humid tropical climatic belt, whereas chlorite and illite are used as proxies of cold and dry conditions or associated to arid environments. Evolution of clay mineral assemblages from the Pliensbachian highlight covariation of kaolinite and chlorite (Figs. 3 and4), which is a very unusual feature and difficult to reconcile in terms of coeval formation in a soil governed by a unique climate. Moreover, as discussed by [START_REF] Thiry | Palaeoclimatic interpretation of clay minerals in marine deposits: an outlook from the continental origin[END_REF], formation of kaolinite-rich laterite and erosion of clay into the oceanic domain require long durations, estimated to more than 1 Myr. The studied area was located between 30° and 40° of palaeolatitude [START_REF] Thierry | Late Sinemurian[END_REF]. On the basis of GCM models and lithological and palaeontological data, the region was subjected to humid to semi-arid climates and megamonsoonal conditions [START_REF] Rees | Jurassic phytogeography and climates: new data and model comparisons[END_REF]Dera et al., 2009a). Evidence of contemporaneous kaolinite-rich soils surrounding basins in the north Tethyan basins has not been demonstrated, and some authors point to the reworking of kaolinite from Palaeozoic rocks instead as the main source [START_REF] Hurst | The implications of clay mineralogy to palaeoclimate and provenance during the Jurassic in NE Scotland[END_REF][START_REF] Jeans | Clay mineralogy of the Jurassic strata of the British Isles[END_REF]. Kaolinite is, for example, reported in Devonian and Carboniferous rocks as detrital and/or authigenic mineral derived from closely emerged landmasses [START_REF] Crasquin | Ostracodes viséens du Nord de la France (Etude paléontologique et analyse de la fraction argileuse)[END_REF][START_REF] Hillier | Clay mineralogy of the Old Red Sandstone and Devonian sedimentary rocks of Wales, Scotland and England[END_REF][START_REF] Shaw | Clay mineralogy of Carboniferous sandstone reservoirs, onshore and offshore UK[END_REF]. The palaeogeography of the north Tethyan domains, as an archipelago with landmasses partly or completely drowned by an epicontinental sea, has also probably reinforced the high proportions of kaolinite in the studied basins by comparison with other basins. Periods of strong chemical and physical erosion by intensive runoff on these continents have therefore likely contributed to increase inherited kaolinite content of contemporaneous marine sediments, while illite and IS R1 corresponded to the background of the clay sedimentation. Therefore, we suggest that the K/I ratio is a reliable proxy to estimate the runoff on continents and inferred humidity/aridity changes that strongly influenced continental weathering during the Pliensbachian (cf. [START_REF] Ruffell | Comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the Mesozoic of NW Europe[END_REF].

Illite, chlorite and kaolinite sources

In the Montcornet and Sancerre boreholes, the clay fraction of the Pliensbachian sediments display unusual features: 1) chlorite is abundant reaching 20% on average, while Jurassic rocks from European sedimentary basins show generally at most 10% of chlorite in their clay fraction (e.g. [START_REF] Ruffell | Comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the Mesozoic of NW Europe[END_REF][START_REF] Deconinck | Environmental controls on clay mineralogy of an Early Jurassic mudrock (Blue Lias Formation, southern England)[END_REF][START_REF] Jeans | Clay mineralogy of the Jurassic strata of the British Isles[END_REF][START_REF] Pellenard | Mineralogical variability of Callovo-Oxfordian clays from the Paris Basin and the Subalpine Basin[END_REF][START_REF] Schnyder | Conjunctive use of clay mineralogy and spectral gamma-ray logs in defining late Jurassic-early Cretaceous palaeoclimate change (Dorset, U.K.)[END_REF]; 2) parallel changes in illite and chlorite proportions are not observed, whereas these primary minerals usually show coeval changes in most sedimentary series, and: 3) instead a co-variation of kaolinite and chlorite is surprisingly highlighted here, even though these two minerals cannot be formed under the same climatic conditions. This coeval kaolinite-and chlorite-rich composition suggests either two distinct sources or a common detrital source with both kaolinite and chlorite inherited from ancient rocks.

The similar temporal evolution of kaolinite and chlorite suggest a common source. The absence of co-variations of chlorite and illite and the co-variation of kaolinite and chlorite could thus be explained by the reworking of authigenic chlorite and kaolinite formed in pore-spaces of old sandstones notably described in the boreal domain along the Fennoscandian Shield [START_REF] Mørk | Mesozoic mudstone compositions and the role of kaolinite weathering -a view from shallow cores in the Norwegian Sea (Møre to Troms)[END_REF]Dera et al., 2009a). We suggest therefore that at least a part of kaolinite and chlorite can be considered as tracers of boreal sources, specifically during periods of high sea-level, when the London-Brabant Massif was flooded (Fig. 7B). By contrast, during periods of sealevel fall, kaolinite and chlorite from boreal domains were likely trapped between the Fennoscandian Shield and the London-Brabant Massif, this latter feeding the northern part of the Paris Basin with smectite (Montcornet, Fig. 7A). High proportions of kaolinite and chlorite occur throughout the Pliensbachian succession of the Cleveland Basin [START_REF] Jeans | Clay mineralogy of the Jurassic strata of the British Isles[END_REF], suggesting continuous input of reworked kaolinite and chlorite from boreal domains, an observation that strengthens this interpretation (Fig. 7).

Climatic events and runoff during the Pliensbachian

Relationships between clay mineralogy and C-O-isotopes

In order to test relationships between clay mineral changes and carbon cycle events in the Tethyan domain, correlations have been attempted between the four studied sections using ammonite biostratigraphy and carbon-isotope chemostratigraphy and by comparing the K/I ratio, considered here as a proxy for runoff on land, to significant negative and positive excursions in carbon isotopes (Fig. 6). Sancerre and Montcornet boreholes cover the top Sinemurian to lowermost Toarcian in the Paris Basin, while Charmouth (Wessex Basin) and Corbigny (Paris Basin) sections provide additional data for the lower Pliensbachian.

During the Late Sinemurian and most of the Early Pliensbachian (up to the Ibex Zone), a low K/I ratio is observed. At the Sinemurian-Pliensbachian boundary, a weak increase in the K/I ratio is recorded at Sancerre (Fig. 6). A coeval increase of kaolinite content is consistently reported in the Lusitanian Basin [START_REF] Caniço | Minerals and clay minerals assemblages in organic-rich facies: the case study of the Sinemurian-Pliensbachian carbonate deposits of the western Lusitanian Basin (Portugal)[END_REF]. This trend is not observed at Montcornet and Charmouth (Fig. 6). It could be explained by either a condensation or hiatus in the Sinemurian-Pliensbachian boundary interval of the two latter sections. Indeed, the Taylori Subzone (first Subzone of the Jamesoni Zone) is not recognised at Montcornet and a hiatus is highlighted at Charmouth [START_REF] Hesselbo | A comparison of the Hettangian to Bajocian successions of Dorset and Yorkshire[END_REF]. This mineralogical change occurred within a negative carbon isotope excursion measured on organic matter in the Sancerre borehole (Peti et al., submitted) and on bulk carbonate at Montcornet (Fig. 6). This negative excursion, at the so-called Sinemurian-Pliensbachian Boundary Event (SPBE), was identified from belemnite carbon-isotope data and organic matter/wood d 13 C in U.K. basins [START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF][START_REF] Price | High-resolution carbon cycle and seawater temperature evolution during the Early Jurassic (Sinemurian-Early Pliensbachian)[END_REF][START_REF] Ruhl | Astronomical constraints on the duration of the Early Jurassic Pliensbachian Stage and global climatic fluctuations[END_REF] and can also be seen in earlier compilations [START_REF] Jenkyns | Chemostratigraphy of the Jurassic System: applications, limitations and implications for palaeoceanography[END_REF]. The same event has been described in the Lusitanian Basin (Duarte et al., 2014), the Asturian Basin [START_REF] Armendáriz | High-resolution chemostratigraphic records from Lower Pliensbachian belemnites: Palaeoclimatic perturbations, organic facies and water mass exchange (Asturian basin, northern Spain)[END_REF][START_REF] Gómez | Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)[END_REF] and the Trento platform [START_REF] Franceschi | Early Pliensbachian (Early Jurassic) C-isotope perturbation and the diffusion of the Lithiotis Fauna: insights from the western Tethys[END_REF]. This negative shift is reported Fig. 8 from the belemnite carbon isotope compilation of [START_REF] Martinez | Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic[END_REF].

From the top of the Ibex Zone to the lower Davoei Zone, the K/I ratio dramatically increase in Montcornet and Sancerre (Fig. 6). This major mineralogical change coincides with a decrease in d 13 C org and d 13 C carb values (Fig. 6) and follows a sea-level lowstand expressed by the occurrence of smectites on the southern borders of the London-Brabant Massif (LBM). This major mineralogical change is consistent with the general increase of the kaolinite input into the NW European domain within the Davoei Zone (Dera et al., 2009a). The K/I increase is also concomitant with more negative d 18 O values measured from belemnite rostra, suggesting warming of sea water [START_REF] Rosales | Paleotemperature variations of Early Jurassic seawater recorded in geochemical trends of belemnites from the Basque-Cantabrian basin, northern Spain[END_REF]Dera et al., 2011a;[START_REF] Armendáriz | High-resolution chemostratigraphic records from Lower Pliensbachian belemnites: Palaeoclimatic perturbations, organic facies and water mass exchange (Asturian basin, northern Spain)[END_REF][START_REF] Martinez | Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic[END_REF]Gómez et al., 2016, Fig. 8).

From the top of the Davoei Zone to the top of the Margaritatus Zone, the K/I ratio remains high at Sancerre and Montcornet with slight variations following three cycles in both boreholes (Fig. 6). These clay mineral cycles likely reflect variations of the runoff triggered by climate in the Milankovitch frequency-band as observed in some Cretaceous sedimentary series [START_REF] Moiroud | High-resolution clay mineralogy as a proxy for orbital tuning: Example of the Hauterivian-Barremian transition in the Betic Cordillera (SE Spain)[END_REF][START_REF] Ghirardi | Multi-proxy orbital chronology in the aftermath of the Aptian Oceanic Anoxic Event 1a: Palaeoceanographic implications (Serre Chaitieu section, Vocontian Basin, SE France)[END_REF]. These runoff cycles are roughly correlated with carbon isotope cycles from organic matter in the Sancerre borehole.

The upper Pliensbachian (Spinatum Zone) is characterised by a sharp decrease of the K/I ratio (Fig. 6), also reported by Dera et al. (2009a). This change precedes an increase in d 13 C carb values and is coeval with maximal d 18 O values. Similar high d 18 O values, recorded in the Lusitanian Basin [START_REF] Oliveira | Avaliação do potencial gerador de petróleo e interpretação paleoambiental com base em biomarcadores e isótopos estáveis de carbono da seção Pliensbaquiano-Toarciano inferior (Jurássico Inferior) da região de Peniche (Bacia Lusitânica, Portugal)[END_REF][START_REF] Suan | Secular environmental precursors to Early Toarcian (Jurassic) extreme climate changes[END_REF], in Spain [START_REF] Rosales | Paleotemperature variations of Early Jurassic seawater recorded in geochemical trends of belemnites from the Basque-Cantabrian basin, northern Spain[END_REF][START_REF] Gómez | Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)[END_REF], in the Cleveland Basin [START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF], and in the Western Carpathians [START_REF] Arabas | Oxygen and carbon isotope records of Lower-Middle Jurassic belemnite rostra and marine carbonates from the Pieniny Klippen Belt (Carpathians)[END_REF], suggest that low runoff occurred during a cooler period (Fig. 8).

Periods of enhanced runoff

Using the K/I ratio as a tracer of humid conditions, at least three periods of enhanced runoff are recognised throughout the Pliensbachian (Fig. 8): 1) the Sinemurian-Pliensbachian boundary, 2) the Lower/Upper Pliensbachian transition (Davoei/Margaritatus Zones), 3) the Subnodosus Subzone (Margaritatus Zone, Upper Pliensbachian).

A long-lasting d 13 C negative excursion of ~2‰, corresponding to the SPBE, encompasses the Sinemurian-Pliensbachian boundary. This carbon excursion recorded in marine carbonates and organic matter has been reported in many localities from the Tethyan domain suggesting a supra-regional or global event [START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF]. A source of isotopically light CO 2 injected into the ocean-atmosphere system is required to explain this 2‰ amplitude negative carbon-isotope excursion, likely suggesting either a volcanic contribution, as proposed by [START_REF] Ruhl | Astronomical constraints on the duration of the Early Jurassic Pliensbachian Stage and global climatic fluctuations[END_REF], or methane release, as discussed for the CIE (Carbon Isotope Excursion) of the T-OAE (Hesselbo et al., 2000a;[START_REF] Hesselbo | Carbon-isotope record of the Early Jurassic (Toarcian) Oceanic Anoxic Event from fossil wood and marine carbonate (Lusitanian Basin, Portugal)[END_REF][START_REF] Hesselbo | Stepwise atmospheric carbon-isotope excursion during the Toarcian Oceanic Anoxic Event (Early Jurassic, Polish Basin)[END_REF][START_REF] Suan | Polar record of Early Jurassic massive carbon injection[END_REF]. A hyperthermal event was highlighted during the T-OAE associated to CO 2 release triggered by Karoo-Ferrar volcanic activity (Pàlfy and Smith, 2000;[START_REF] Jourdan | The 40 Ar/ 39 Ar ages of the sill complex of the Karoo large igneous province: Implications for the Pliensbachian-Toarcian climate change[END_REF] and/or methane hydrate reservoir disruption (Hesselbo et al., 2000a;[START_REF] Jenkyns | Geochemistry of oceanic anoxic events[END_REF]. The subsequent high pCO 2 favoured: 1) concomitant large organic matter accumulations (black-shale deposits) (e.g. [START_REF] Jenkyns | The early Toarcian (Jurassic) anoxic event: stratigraphic, sedimentary, and geochemical evidence[END_REF][START_REF] Jenkyns | Geochemistry of oceanic anoxic events[END_REF][START_REF] Baudin | Distribution of organic matter during the Toarcian in the Mediterranean Tethys and Middle East[END_REF], and; 2) runoff and continental weathering increases, expressed by a set of isotope data (Sr, Os, Ca ...) (Jones andJenkyns, 2001, Bailey et al., 2003;[START_REF] Cohen | Osmium isotope evidence for the regulation of atmospheric CO2 by continental weathering[END_REF][START_REF] Brazier | Calcium isotope evidence for dramatic increase of continental weathering during the Toarcian oceanic anoxic event (Early Jurassic)[END_REF][START_REF] Ruhl | Astronomical constraints on the duration of the Early Jurassic Pliensbachian Stage and global climatic fluctuations[END_REF] and sedimentological evidence, including change in clay mineral proportions [START_REF] Hermoso | Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to the middle Toarcian in the Paris Basin[END_REF]. A similar increase in pCO 2 is interpreted by the D 13 C (d 13 C carbd 13 C org ) during the SPBE (van de [START_REF] Van De Schootbrugge | Early Jurassic climate change and the radiation of organic-walled phytoplankton in the Tethys Ocean[END_REF]. Organic matter-rich sediment including black shale was also deposited in dysoxic to anoxic environments during the latest Sinemurian [START_REF] Rosales | Paleotemperature variations of Early Jurassic seawater recorded in geochemical trends of belemnites from the Basque-Cantabrian basin, northern Spain[END_REF][START_REF] Boussaha | Spatial characterization of the late Sinemurian (Early Jurassic) palaeoenvironments in the Lusitanian Basin[END_REF], Duarte et al., 2014). Besides the kaolinite enrichment observed in this study, proxies of continental weathering and runoff are also reported, including, for example, eutrophic conditions linked to higher nutrient input from continents preventing the widespread occurrence of the Lithiotis fauna [START_REF] Franceschi | Early Pliensbachian (Early Jurassic) C-isotope perturbation and the diffusion of the Lithiotis Fauna: insights from the western Tethys[END_REF].

Temperature reconstructions for the SPBE are still debated but no evidence of hyperthermal temperatures has been described, in contrast to the T-OAE. A warm period is suggested during the latest Sinemurian based on belemnites from the Asturian Basin [START_REF] Gómez | Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)[END_REF], whereas a slight cooling trend is recorded by belemnites and bivalves in the Cleveland Basin [START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF]. However, cool bottom water temperatures described in the Cleveland Basin may reflect local deep water conditions and bias temperature reconstruction of this period [START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF]. This event was rather interpreted as a greenhouse interval [START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF], consistent with a humid climate and consequently enhanced runoff on landmasses, as supported by our data.

The Lower/Upper Pliensbachian transition (e.g. Davoei Zone-Stokesi Subzone) may display the most obvious change in runoff conditions during the Pliensbachian with a generalised and dramatic increase in the kaolinite input to the NW European Basins (Fig. 8).

Interestingly, this period coincides with: 1) a slight change in the 87 Sr/ 86 Sr curve characterised by a plateau, suggesting enhanced continental weathering, while a broad decrease of 87 Sr/ 86 Sr values is recognised throughout the Pliensbachian, hypothetically linked to sea-floor spreading [START_REF] Jones | Strontium isotopes in Early Jurassic seawater[END_REF][START_REF] Jones | Seawater strontium isotopes, Oceanic Anoxic Events, and sea-floor hydrothermal activity in the Jurassic and Cretaceous[END_REF]; 2) rising sea temperatures inferred from oxygen isotope belemnite data (Dera et al., 2009b;2011a;[START_REF] Martinez | Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic[END_REF][START_REF] Gómez | Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)[END_REF]; 3) occasional black shale deposits in the Lusitanian Basin [START_REF] Silva | Organic matter production and preservation in the Lusitanian Basin (Portugal) and Pliensbachian climatic hot snaps[END_REF]; 4) a decrease in ammonite species richness observed in the NW European and Mediterranean domains likely triggered by warming [START_REF] Dommergues | Ammonite diversity and its palaeobiogeographical structure during the early Pliensbachian (Jurassic) in the western Tethys and adjacent areas[END_REF].

These lines of evidence highlight warmer and more humid conditions at the base of the Davoei Zone. However, this interval is also characterised by a change in the detrital supply shifting to boreal sources (see section 5.2.3), and a suggested change in water mass circulation in the NW European domain. In the Davoei Zone, more radiogenic eNd values recorded in fish teeth imply an input of water mass affected by young and more radiogenic rocks what may correspond to sources from the Panthalassa ocean or more likely from low latitudes of the Tethys Ocean (Dera et al., 2009b;[START_REF] Dera | Nd isotope constraints on ocean circulation, paleoclimate, and continental drainage during the Jurassic breakup of Pangea[END_REF]. This apparent paradox between detrital flux from the Fennoscandian Shield and radiogenic water input originating from the south may be explained by a rising sea-level favouring connections between sedimentary basins and a new current pattern (Fig. 7). The subsequent flooding of the London-Brabant Massif would allow kaolinite and chlorite inputs into the Paris and Wessex basins from the north. These palaeoceanographic and palaeogeographic changes are consistent with mixing of ammonite faunas from euro-boreal domains recognised during the Davoei Zone (Dera et al., 2011b).

Finally, the Lower/Upper Pliensbachian transition is characterised by two major environmental disruptions: 1) a warming episode associated to enhanced runoff, and; 2) rising sea-level and palaeoceanographic changes. These conditions contributed to explain the dramatic clay mineralogical change observed in NW European domains.

In the Margaritatus Zone, the K/I ratio displays weak fluctuations likely triggered by variability in runoff intensity. The maximum values (i.e. Subnodosus Subzone), coincide with the occurrence of organic matter-rich sediment and black shale deposits reported as the Late Pliensbachian Organic-Rich Preservation Interval (OMPI; [START_REF] Rosales | Paleotemperature variations of Early Jurassic seawater recorded in geochemical trends of belemnites from the Basque-Cantabrian basin, northern Spain[END_REF][START_REF] Silva | Update of the carbon and oxygen isotopic records of the Early-Late Pliensbachian (Early Jurassic, ~187 Ma): Insights from the organic-rich hemipelagic series of the Lusitanian Basin (Portugal)[END_REF][START_REF] Armendáriz | High-resolution chemostratigraphic records from Lower Pliensbachian belemnites: Palaeoclimatic perturbations, organic facies and water mass exchange (Asturian basin, northern Spain)[END_REF][START_REF] Caruthers | The Pliensbachian-Toarcian (Early Jurassic) extinction: A North American perspective[END_REF][START_REF] Silva | Organic matter production and preservation in the Lusitanian Basin (Portugal) and Pliensbachian climatic hot snaps[END_REF][START_REF] Neumeister | Oceanic response to Pliensbachian and Toarcian magmatic events: Implications from an organic-rich basinal succession in the NW Tethys[END_REF]. Maximal runoff within Subnodosus Subzone likely triggered an increase in organic productivity through the associated increase in the nutrient supply.

Glacio-eustasy during the Pliensbachian?

The possibility for glacio-eustasy should be addressed because smectite events in the north Paris Basin clearly indicate emersion of the London Brabant Massif (LBM) during sealevel fall, while the absence of this mineral highlights its flooding during sea-level rise (Figs. 7 and8). Such a great palaeogeographic change likely resulted from the flatter and lower topography of the LBM compared to other Palaeozoic massifs because of its external position in the Variscan belt. Alternating emersion and flooding of the LBM with relatively short durations (i.e. <1 Myr) and high amplitude variations of the sea-level, at least several tens of metres, appears more consistent with a glacio-eustasy model than a regional uplift. Indeed regional uplift associated to the Cimmerian tectonic phases, described for the LBM, seems have been progressive with moderate speed of unroofing throughout the Jurassic from apatite fission track data [START_REF] Vercoutere | Post-Palaeozoic cooling and uplift of the Brabant Massif as revealed by apatite fission track analysis[END_REF]. The smectite events are recorded within the Ibex and Spinatum Zones, which correspond to cooler intervals as expressed in oxygen isotope data (Fig. 8 and Suppl. Mat. Fig. 1). This is particularly clear in the Spinatum Zone, for which time ice-cap growth has been previously suggested from sedimentological and isotope data [START_REF] Price | The evidence and implications of polar ice during the Mesozoic[END_REF][START_REF] Suan | Polar record of Early Jurassic massive carbon injection[END_REF], Dera et al., 2011a, 2011b;[START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF][START_REF] Arabas | Oxygen and carbon isotope records of Lower-Middle Jurassic belemnite rostra and marine carbonates from the Pieniny Klippen Belt (Carpathians)[END_REF]. This inference is also consistent with a relatively low pCO 2 (around 900 ppm) inferred from stomatal density from Araucariacea leaves [START_REF] Steinthorsdottir | Early Jurassic (late Pliensbachian) CO 2 concentrations based on stomatal analysis of fossil conifer leaves from eastern Australia[END_REF]. In this cooler interval, the K/I ratio dramatically drops suggesting reduced humidity, slowing down of the water cycle, and subsequent low runoff (Fig. 8). Combined with the sealevel fall inferred from the uppermost part of the Pliensbachian, this situation strengthens a glacio-eustatic control. A similar situation occurred from the probably topmost part of the Jamesoni Zone to the lower part of the Ibex Zone, where low K/I ratio and smectite occurrence are observed together with higher values in bulk d 18 O carb within a regressive trend and a low stand of sea-level (Fig. 8 and Suppl. Mat. Fig. 2). These coincident changes are consistent with the formation of ice at high latitudes during the interval that spans the Ibex Zone, although belemnite oxygen isotope data are more scattered and do not show any clear cooling (Fig. 8).

Changes in the SMOW values during the cold snap and the subsequent deglaciation, providing fresh water input and salinity variations, could also be responsible for the scattered oxygen isotope data. Recent isotope data from belemnite in the Dorset (U.K.) are consistent with a relatively cold Jamesoni-Ibex interval compared to the warmer Davoei interval [START_REF] Price | High-resolution carbon cycle and seawater temperature evolution during the Early Jurassic (Sinemurian-Early Pliensbachian)[END_REF]. The following warming and deglaciation, combined with the sea level rise, likely enhanced runoff and reworking of ancient kaolinite and chlorite-bearing sediments and rocks from the Fennoscandian Shield. This climatic story is consistent with oxygen isotope data published in the Basque-Cantabrian and Asturian Basins [START_REF] Rosales | Geochemical arguments for identifying second-order sea-level changes in hemipelagic carbonate ramp deposits[END_REF][START_REF] Armendáriz | High-resolution chemostratigraphic records from Lower Pliensbachian belemnites: Palaeoclimatic perturbations, organic facies and water mass exchange (Asturian basin, northern Spain)[END_REF].

Conclusions

Clay mineral and paired carbon-oxygen-isotope data have been generated from two boreholes in the Paris Basin representing an interval from the latest Sinemurian to the earliest Toarcian, with additional mineralogical data from sections in the Paris and Wessex Basins. The diversity of clay assemblages results from the complex interplay of several detrital sources, sea-level change, seaway circulation, and runoff. The following features interpreted in terms of climate and palaeoceanographic changes are highlighted:

-Increasing kaolinite/illite ratio characterises periods of enhanced runoff, during: i) the Sinemurian-Pliensbachian transition associated with a negative carbon excursion (SPBE); ii) the Early/Late Pliensbachian transition (Davoei Zone-Stokesi Subzone), and; iii) the Subnodosus Subzone (Late Pliensbachian, Margaritatus Zone). These periods correspond to warm and humid climates, favouring continental weathering and subsequent black shale deposition. By contrast, cooler periods with low runoff occurred during the Jamesoni -Ibex and the Spinatum Zones.

-The influence of climate forcing on clay assemblages is magnified by palaeoceanographic changes and sea level fluctuations. A dramatic change in clay mineralogy is notably observed for the Davoei Zone, characterised by kaolinite and chlorite-rich sedimentation. We suggest that these minerals were likely reworked from ancient sediments and rocks from the Fennoscandian Shield during a high sea-level period favouring connections between sedimentary basins and flooding of the London Brabant Massif. By contrast, this massif was emerged during periods of sea-level lowstand and acted as a topographic barrier.

-Two smectite-rich intervals occurred in the north Paris Basin during the two periods of sealevel lowstand (Ibex and Spinatum Zones). These features are limited to the margin of the London Brabant Massif, which was a unique source of smectite. These smectite events highlight recurrent emersions of the London Brabant Massif, characterised by a flat and low topography, and suggest significant amplitude of the sea-level fluctuation that could be explained by glacioeustasy. Smectite-rich intervals in the north Paris Basin may thus emphasize continental ice growth at times during the Early Jurassic (i.e. late Jamesoni/early Ibex Zones and Spinatum Zone). Figure 8. Summary of clay mineral data, geochemical data, and organic matter accumulations from the end Sinemurian to the early Toarcian, reported against numerical ages, biostratigraphic framework based on ammonites and sequence stratigraphy of the Tethyan domain [START_REF] Jacquin | Major transgressive/regressive cycles: the stratigraphic signature of European basin development. Mesozoic and Cenozoic Sequence Stratigraphy of European basins[END_REF][START_REF] Gradstein | The Geologic Time Scale 2012[END_REF]: Smectite events (this study); d 18 O from belemnites (dataset from [START_REF] Martinez | Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic[END_REF] with red intervals corresponding to warm periods and blue intervals to cold periods; runoff based on the K/I ratio (this study), with position of small K/I increase (1, 2, 3) and major K/I increase (A) and decrease (B); d 13 C from organic matter [START_REF] Hesselbo | Massive dissociation of gas hydrate during a Jurassic oceanic anoxic event[END_REF][START_REF] Hesselbo | Carbon-isotope record of the Early Jurassic (Toarcian) Oceanic Anoxic Event from fossil wood and marine carbonate (Lusitanian Basin, Portugal)[END_REF][START_REF] Van De Schootbrugge | Early Jurassic climate change and the radiation of organic-walled phytoplankton in the Tethys Ocean[END_REF][START_REF] Suan | Secular environmental precursors to Early Toarcian (Jurassic) extreme climate changes[END_REF][START_REF] Korte | Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic[END_REF], d 13 C from bulk carbonates [START_REF] Oliveira | Avaliação do potencial gerador de petróleo e interpretação paleoambiental com base em biomarcadores e isótopos estáveis de carbono da seção Pliensbaquiano-Toarciano inferior (Jurássico Inferior) da região de Peniche (Bacia Lusitânica, Portugal)[END_REF][START_REF] Silva | Update of the carbon and oxygen isotopic records of the Early-Late Pliensbachian (Early Jurassic, ~187 Ma): Insights from the organic-rich hemipelagic series of the Lusitanian Basin (Portugal)[END_REF]Duarte et al., 2014; this study) and d 13 C from belemnite data [START_REF] Martinez | Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic[END_REF], with yellow intervals corresponding to main negative carbon excursions; black shale occurrence (black point), the point size indicates their record extent [START_REF] Rosales | Paleotemperature variations of Early Jurassic seawater recorded in geochemical trends of belemnites from the Basque-Cantabrian basin, northern Spain[END_REF][START_REF] Oliveira | Avaliação do potencial gerador de petróleo e interpretação paleoambiental com base em biomarcadores e isótopos estáveis de carbono da seção Pliensbaquiano-Toarciano inferior (Jurássico Inferior) da região de Peniche (Bacia Lusitânica, Portugal)[END_REF][START_REF] Silva | Update of the carbon and oxygen isotopic records of the Early-Late Pliensbachian (Early Jurassic, ~187 Ma): Insights from the organic-rich hemipelagic series of the Lusitanian Basin (Portugal)[END_REF][START_REF] Armendáriz | High-resolution chemostratigraphic records from Lower Pliensbachian belemnites: Palaeoclimatic perturbations, organic facies and water mass exchange (Asturian basin, northern Spain)[END_REF][START_REF] Boussaha | Spatial characterization of the late Sinemurian (Early Jurassic) palaeoenvironments in the Lusitanian Basin[END_REF][START_REF] Duarte | Carbon isotope stratigraphy and ammonite biochronostratigraphy across the Sinemurian-Pliensbachian boundary in the western Iberian margin[END_REF]; 87 Sr/ 86 Sr curve [START_REF] Jones | Strontium isotopes in Early Jurassic seawater[END_REF] and eNd curve (Dera et al., 2009b).

Supplementary material:

  domain well-constrained by ammonites and/or calcareous nannofossils. Relationships between clay mineralogy, d 13 C excursions, and d 18 O fluctuations are carefully examined in order to decipher the role of the carbon cycle and temperature evolution on continental weathering changes. Palaeoceanographic changes, eustatic variations, and detrital sources, are also discussed in relation to palaeoclimate changes.

  0‰) is observed between 929.4 m and 908 m from the Raricostatum Zone (Upper Sinemurian) to an undefined zone between the Jamesoni and Ibex Zones (Lower Pliensbachian). A recovery phase between 908 m and 892 m is marked by a positive trend with values which are going up from 0‰ to 1.5‰, covering the possible upper Jamesoni Zone and of the lower Ibex Zone. The Valdani Subzone (Ibex Zone) is characterised by a plateau from 892 m to 878 m with values around 1.5‰. A second positive shift around 2‰ is observed between 878 m and 869.5 m from the top of the Valdani Subzone and the top of the Ibex -lowermost part of the Davoei Zone, before values decrease to 1.5‰ between 869.5 m and 866 m. Then a first negative shift with an amplitude of 1.8‰ is observed between 866 m and 862.5 m (Maculatum Subzone, Davoei Zone) followed by a low rebound from 862.5 m to 854m with values ranging from -0.25‰ to 0.25‰ (Capricornus and lower Figulinum Subzones, Davoei Zone). A second strong decrease (at least -3‰) is observed between 854 m and 846 m in the Figulinum Subzone (Davoei Zone) and keep fluctuating between -0.5‰ and -4‰ to 794 m. From 794 m, d 13 C values increase to 0.6‰ and fluctuate up to 1.2‰ to 782 m. Then, values slightly decrease down to 0.4‰ (773 m)

  highlight the negligible influence of diagenesis. However, scattered and anomalous negative values of d 13 C carb are observed throughout a very argillaceous interval between 789 m and 862 m, corresponding to the Late Pliensbachian (Davoei and Margaritatus Zones). This interval contains frequent red nodules of siderite with occasional Zn-mineralisation (sphalerite), (Fig. 2) likely due to reducing conditions occurring during early diagenesis, even if late fluid circulations cannot be ruled out. The disturbed d 13 C carb signal obtained here which prevents the use of bulk carbonate carbon isotope values for palaeoenvironmental reconstructions is mainly explained by low carbonate contents. The d 18 O carb values in the Montcornet borehole are scattered, particularly in the 789 m to 862 m siderite-nodule-bearing interval indicating thorough fluid circulation.. Trends are yet observed at the base and the top of the borehole with higher values between 905 m and 890 m

Figure 1 .

 1 Figure captions:

Figure 2 .

 2 Figure 2. Detailed lithology, sampling and ammonite biostratigraphy of the Montcornet

Figure 3 .

 3 Figure 3. Biostratigraphy, lithology, sequence stratigraphy, clay mineralogy, K/I

Figure 4 .

 4 Figure 4. Biostratigraphy, lithology, sequence stratigraphy, clay mineralogy, K/I

Figure 5 .

 5 Figure 5. Scanning Electron Microscope from samples of Montcornet. A-B) views of a

Figure 6 .

 6 Figure 6. Correlation between Sancerre and Montcornet boreholes (Paris Basin) and two

Figure 7 .

 7 Figure 7. Palaeomaps and schematic cross-sections for clay minerals sourcing in: A) sea-level

Fig. 1 :

 1 Fig. 1: Biochronology from North-Western Europe and distribution of ammonites fauna in the

Fig. 2 :

 2 Fig. 2: d 13 C and d 18 O values from bulk carbonate in the Montcornet borehole (Northern Paris

  Fig 1

Table 1 :

 1 Sampled and identified ammonites in the Montcornet borehole

Table 2 :

 2 Clay mineral proportion in the Montcornet borehole. (IS R0: R0 type illite smectite

mixed-layer; C: chlorite; IS R1: R1 type illite smectite mixed-layer; I: illite; K: kaolinite; K/I: kaolinite/illite ratio.

Table 3 :

 3 Clay mineral proportion in the Montcornet borehole. (IS R0: R0 type illite smectite mixed-layer; C: chlorite; IS R1: R1 type illite smectite mixed-layer; I: illite; K: kaolinite; K/I: kaolinite/illite ratio.

Table 4 :

 4 d 13 C and d 18 O form bulk carbonate values (expressed in ‰) in the Montcornet borehole.

Acknowledgements

The study was supported by the "Agence Nationale pour la Gestion des Déchets Radioactifs" (Andra--French National Radioactive Waste Management Agency). We are grateful to P. Landrein and C. Aurière for access to the Andra core store and P. Neige for Toarcian ammonite determination. The authors thank S. Bodin and an anonymous reviewer for their helpful comments.