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Duricrusts are hard elemental layers forming in tropical and subtropical regions. Different types of duricrusts exist, including calcretes, silcretes and ferricretes (or iron duricrusts), that differ by their composition and, most likely, their formation mechanism. In places such as Africa, Australia or Brazil, we can observe them capping hills and protecting landscapes, thus being an important part of regional geomorphology. Their formation is highly dependent on climate and requires strong seasonal precipitation cycles, enabling transport and accumulation of elements during wet seasons and precipitation and hardening during dry seasons. However, it is also known that duricrusts form in tectonically quiet environments, and multiple tens of thousands of years are needed to form centimetres to metres thick elemental layers. Two hypotheses for duricrust formation exist, namely the water table (or horizontal) hypothesis and the laterite (or vertical) hypothesis. Yet, until recently, no quantitative (numerical) model exists that represents either of them. We presented last year (Fenske et al, 2022) a model based on the water table hypothesis. Here we present a second model based on the laterite hypothesis and compare the predictions of the two models. Although the models we propose are potentially applicable to a wide range of duricrusts, we will concentrate here on the formation of ferricretes.Laterites are a type of regolith covering around 33\% of land surfaces. The thickest lateritic profiles are found in the centre of continental cratons, where they evolved for millions of years. The main process responsible for laterisation is weathering, the process transforming bedrock into regolith. During weathering rocks progressively lose their structure, elements are dissolved, re-precipitated, leached, or transported, leading to progressive porification and compaction. Subsequently, from the weathering front to the surface, a typical lateritic profile is made of coarse grained and then fine grained saprolite, a mottled zone and at the top, an indurated cover, the ferricrete. We recently developed a numerical model for duricrust formation according to the laterisation hypothesis (LT model). In this model, iron duricrusts are genetically linked to the bed rock. Material from the bedrock are transformed and leached within a given vertical column of rocks but are also moved vertically due to tectonic uplift. We assume that as the regolith ages, it undergoes a process of transformation that is proportional to mean fluid flow and that leads to hardening and compaction. As material is constantly removed from the regolith layer, the model is dependant on a constant material input (through uplift and, potentially, surface erosion) to reach sufficient laterisation for ferricrete formation. Comparing predictions of the laterisation (LT) model to those of the water table (WT) model, we observe that they require slightly different tectonic regime, with the WT model most efficient during period of complete quiescence and the LT model needing a slow constant rate of base level fall to produce duricrusts. The two models also differ by the geometry of the duricrusts they predict and, in particular, the depth at which duricrust forms in the regolith (at or above the water table level).

The Pyrenean system has been largely studied in its globality from the tectono-sedimentary evolution of the retro and pro-foreland basins (sinks) to the exhumation history of the Axial Zone (sources) constrained by thermochronological studies. The present estimation of the siliciclastic sediment volumes from the entire South Pyrenean pro-foreland basin completes the recent measurements made from the Aquitanian retro-foreland basin by using the same methodology. A re-evaluated complete budget of the deposited material in the southern foreland basins (South Pyrenean zone, Ebro basin and Valencia gulf) derived exclusively from the Pyrenean domain is proposed for the Early Eocene-Holocene period (56-0 Ma). Measurement of the compacted siliciclastic sediment volume is based on isopach maps (thickness maps) from Lanaja., 1987 for the Ebro and South Pyrenean zone, while volumes of the Valencia gulf were calculated from R. Pellen 2016.The volumes from the Eocene period (56-33.9Ma) will allow comparison of deposited siliciclastic sediments in both northern and southern sinks and the eroded volumes at the scale of the entire orogen (obtained from the interpolation of compiled thermochronological data) in the light of a source to sink approach.References:Lanaja, J. M. (1987). Contribución de la exploración petrolífera al conocimiento de la geología de España. IGME.Pellen Romain (2016). Géodynamique et impact de la crise d'érosion et de salinité Messinienne sur les transferts sédimentaires (bassins de Valence et Adriatique). PhD Thesis, Université Bretagne Loire. https://archimer.ifremer.fr/doc/00406/51714/

International audience; In order to understand the effects of the OAE1a on the sedimentary system in a Source to Sink approach, we studied the Late Barremian-Aptian sediments of the Wessex-Channel and Weald Basins and present a synthesis of the sequence stratigraphic framework and sedimentary patterns of the siliciclastic system developed during this time interval. We present a regional and detailed sequence stratigraphic model for the Lower Greensand Group and provide new stratigraphic insights.This synthesis is based on field work (Isle of Wight) with focus on defining sedimentological and stratigraphic signatures using facies analysis and is coupled with published datasets and studies on bio- chemo-stratigraphy. The results are integrated with well-logs correlations for regional scale understanding.It presents updated composite lithostratigraphic logs for three areas of the island which are correlated and provide a better 3D understanding for this part of the basin. The analysis and interpretation of the well database (84 petroleum exploration wells) contributed to understanding the regional architecture including the extent, facies distributions and thickness variations of the sediments. The sequence stratigraphic model includes 3rd order (composite) sequences within the context of 2nd order super-sequences and a nomenclature in support of the model was proposed. Also, on the Isle of Wight, we present how the sedimentary system along with the relative sea level variations additionally recorded significant changes in terms of depositional environments. Finally, the applicability of the sequence stratigraphic model will be examined on a global scale for the proposal of a unified regional nomenclature in accordance with the global understanding of eustatic variations. Therefore, a long-distance correlation with already established schemes will be performed including France, Spain, the Southern Tethyan margin (Tunisia) and the Arabian plate.The project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No 860383 (https://www.s2s-future.eu/).

Nile River, the longest river in the world (>6,500 km), has been studied since long time ago tracing back to the fifth century yet the timing of origin of its present-day drainage is still disputed. There are two end-members of notions of the birth of the Nile, the first one believes that the present-day Nile has been connected to the Ethiopian Plateau since ~30 Ma, while the other supports the idea of young Nile around ~6 Ma. The Nile crosses today two former endorheic systems (Sudanese and Albertine “Basins”) and one exorheic system (Tethys Margin) before finally depositing sediments in the Mediterranean Sea. Our objective here focuses on deciphering the source-to-sink scenario of the Nile through relief growth, tectonic, and climate since the uppermost Cretaceous.The timing of the uplifts and deformation wavelengths are constrained by characterizing and mapping several generations of stepped pediments on DEM and satellite images which then dated using their geometrical relationships with dated magmatic rocks. Additionally, stratigraphic records of the sedimentary basins were studied to complement the dating of the pediments. The authenticity of the approaches is to integrate those data enclosing all the source-to-sink (S2S) systems to construct a coherent scenario of the Nile paleorouting systems especially on the dynamics of its sediment sources.We proposed the following model for the S2S of the Nile where its catchment grew larger southwards through time. First, a significant deformation occurred around the Cretaceous-Paleogene boundary (66 Ma) with the uplift of western limit of the Nile catchment, the Darfur-Ennedi-Tibesti domains, followed by the formation of a main large pediment. Second, this pediment was then flooded during late Paleocene (58-57 Ma) until a subtle high bounding northward the endorheic Sudanese “Basin”. Consequently, carbonate platforms were widely deposited from Paleocene until middle Eocene in the Egypt extending southwards to the former Hudi Lakes in northeast Sudan and there was no siliciclastic supply for the Nile during that time. Third, the first evidence of a fluvial system (“Pre-Eonile” according to Said, 1981) was discovered during late Eocene (~37 Ma) by large channel incisions on top of the carbonate platforms. Contemporaneously, the Uweinat Dome was uplifted and likely acted as the main siliciclastic source during late Eocene to Oligocene. Fourth, the initiation of Red Sea rifts during the Oligocene followed by a major uplift at the scale of north-east Africa (~10 Ma) provoked another plausible siliciclastic source, the Red Sea Hill’s flanks, in addition to the Uweinat Dome. Fifth, during the capture of the Sudanese endorheic system in the Early Pliocene (~4 Ma), the Nile catchment grew significantly larger and the sources were actively provided by the Darfur and Ethiopian Plateau. Finally, during middle-late Pleistocene (< 1 Ma) the Nile completed its present-day catchment by capturing the Albertine endorheic system and the siliciclastic sediments were supplied by the Ethiopian Plateau and the East African Dome.

Recent studies have coupled the Lu-Hf and Sm-Nd isotopic systems on clay fractions to assess the evolution of chemical weathering in both ancient and modern environments. Results of this proxy in the abyssal plain of the Cape Basin in Southwestern Africa show a concomitant increase of chemical weathering and physical erosion in response to a late Cretaceous tectonic uplift. In this study, we performed analyses on sediments in the continental slope of the basin that show significant differences compared to the abyssal plain: A long-steady decrease in quartz simultaneous to an increase in the calcite content during the late Cretaceous; a lower content of detrital smectite throughout the section; and the presence of mixed layer assemblages of illite – smectite (R0 or R1) and vermiculite – chlorite during the early-late Cretaceous transition, coinciding with the period of low carbonate content. First, these differences indicate a variation in the input of siliciclastic material and a change in the carbonate compensation depth. Second, clay assemblages reveal a burial diagenetic influence compared to those recorded in the abyssal domain, likely due to thicker deposition in the continental slope. These diagenetic processes indicate that there is a perturbation in the chemical weathering signal at the continental slope, therefore the disparities between the denudation record on clays in both segments cannot be attributed to an effect of signal propagation due to this post-deposition processes.

International audience; The modern relief of southern Africa is characterized by high-standing plateaus surrounded by escarpments and dissected by a network of encased valleys that connect the plateaus to coastal plains. This topography is commonly interpreted as resulting from the activity of a mantle plume, the African superplume, and the resulting stepwise uplift of the lithosphere, generating planation surfaces through surface erosion processes since the Mesozoic. However, in this study, we argue that part of this landscape is inherited from the glacial processes of the Late Paleozoic Icehouse (LPI) that occurred 300 ma ago and during which southern Africa was largely covered in thick ice. Field and GIS-based sedimentological and geomorphological studies however revealed that LPI glacial activity tied to the Late Paleozoic Icehouse, that occurred 300 million years ago and during which southern Africa was largely covered in thick ice, greatly contributed to the shaping of the Earth surface at different spatial scales. Glaciers levelled continental-scale planation surface, carved large valleys, fjords and overdeepenings within topographic escarpments that already existed, ploughed grooves and striae on the bedrock and left behind typical sediments such as moraines, tills and ice-contact deltas. After glacial retreat, the sea invaded these glacial reliefs, as attested by preserved paleoshorelines. In postglacial times and for 120-180 million years, these glacial landforms were progressively filled and eventually sealed under thick non-glacial sedimentary accumulation and was later rejuvenated by erosion tied to the activity of the mantle superplume. Today, large portions of the desertic high-standing plateaus, escarpments and networks of valleys defining the relief of southern Africa actually corresponds to a relict though rejuvenated 300-Ma old glacial landscape.

In the past two decades, adeno-associated virus (AAV) vector manufacturing has made remarkable advancements to meet large-scale production demands for preclinical and clinical trials. In addition, AAV vectors have been extensively studied for their safety and efficacy. In particular, the presence of empty AAV capsids and particles containing “inaccurate” vector genomes in preparations has been a subject of concern. Several methods exist to separate empty capsids from full particles; but thus far, no single technique can produce vectors that are free of empty or partial (non-unit length) capsids. Unfortunately, the exact genome compositions of full, intermediate, and empty capsids remain largely unknown. In this work, we used AAV-genome population sequencing to explore the compositions of DNase-resistant, encapsidated vector genomes produced by two common production pipelines: plasmid transfection in human embryonic kidney cells (pTx/HEK293) and baculovirus expression vectors in Spodoptera frugiperda insect cells (rBV/Sf9). Intriguingly, our results show that vectors originating from the same construct design that were manufactured by the rBV/Sf9 system produced a higher degree of truncated and unresolved species than those generated by pTx/HEK293 production. We also demonstrate that empty particles purified by cesium chloride gradient ultracentrifugation are not truly empty but are instead packaged with genomes composed of a single truncated and/or unresolved inverted terminal repeat (ITR). Our data suggest that the frequency of these “mutated” ITRs correlates with the abundance of inaccurate genomes in all fractions. These surprising findings shed new light on vector efficacy, safety, and how clinical vectors should be quantified and evaluated.

International audience; We use a Landscape Evolution Model including flexural isostasy to investigate the influenceof inherited foreland relief on the stratigraphic evolution of the retro-foreland domain during mountainbuilding. We show models with four different types of initial relief in the foreland domain: at sea level,elevated (+300 m), a 1 km-deep and 100 km-wide foreland basin associated with either a forebulge at sealevel or elevated at +300 m. During the first 10 Myr of simulation, the landscape evolution of the foreland issignificantly altered by its inherited bathymetry/topography. The impact is then smoothed out once the foreland slope has stabilized and develops a transverse drainage network. Models record a long-term shallowing-up mega-sequence driven by the increase in sediment production rate in the uplifting range and the decrease in the rate of flexural accommodation space creation in the foreland basin. The initial relief of the foreland domain alters the timing of its transition from the under-filled to the over-filled phase. An initially deep foreland basin is twice as thick as an initially elevated foreland. It records deep marine deposits while a foreland initially at sea level records thin shallow marine and an elevated foreland records continental deposits. The forebulge is buried by continental deposits in an initially elevated foreland while it is buried by marine sediments in other models. Alluvial fans at the foot of the range are more elevated in initially elevated forelands. We discuss our results of modeled stratigraphic architecture in comparison with the Pyrenean, Alpine and Andean retro-foreland basins.

International audience; We present a study to estimate the large-scale landscape history of a continental margin, by establishing a source-to-sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best-fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale, a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate.

International audience; L’ensemble des données et connaissances acquises sur la chaine Pyrénéenne et l’évolution de ces bassins d’avant-pays permettent à présent d’appréhender ce système orogénique et l’évolution des bassins dans une perspective source to sink intégrée. Cette approche met en relation l’ensemble du routage sédimentaire depuis la Source (relief orogénique, craton, recyclage de bassin) en passant par la zone de transfert (périphériques ou internes au bassin) jusqu’au réservoir final (bassin flexural, bassin turbiditique profond). Nous proposons d’intégrer l’ensemble de ces données sous la forme d’une nouvelle cartographie, sur l’ensemble du domaine péri-pyrénéen du Golfe du Lion à l’Est jusqu’au Golfe de Gascogne à l’Ouest en incluant le Massif Armoricain au Nord jusqu’au bassin de Madrid au Sud. Cette représentation en cartes est complétée par des diagrammes de Wheeler « augmentés » intégrant l’évolution des reliefs. La réalisation de ces cartes s’appuie sur l’utilisation de nombreuses méthodes et outils, tels que les reconstructions cinématiques du système Ibérie-Europe-Méditerranée, les coupes restaurées, l’histoire d’exhumation par thermochronologie, le traçage des sources, la caractérisation des surfaces d’altération et d’érosion, la synthèse de l’activité des accidents structuraux majeurs, les reconstructions paléogéographiques, l’analyse des géométries sédimentaires et des directions de transport ainsi que la quantification des volumes préservés dans les bassins. Nous présenterons ici des cartes représentatives de l’évolution du routage sédimentaire au cours des premières phases de l’orogenèse du Danien au début du Bartonien. Les pas de temps choisis pour ces cartes permettent de rendre compte de différents stades d’évolution tectono-sédimentaire du système péri-pyrénéen au stade de quiescence de l’orogenèse (1) à 65 Ma, Danien, et aux stades précoces de l’orogenèse (2) Thanétien terminal (56Ma) et (3) Yprésien (52 Ma), jusqu’au début de la collision Bartonien (40 Ma). Les compilations effectuées mettent en regard domaines exhumés et zone de sédimentation en termes de flux et de volumes, et permettent de cartographier les systèmes de routage et leur évolution au cours d’un cycle de construction d’un orogène. Elles mettent en évidence l’influence du diachronisme Est Ouest de la compression pyrénéenne et de la déformation de l’avant pays sur le routage sédimentaire, l’importance de la contribution des reliefs périphériques aux budget sédimentaires au cours de l’évolution du système source to sink et de discuter de l’influence des variations climatiques sur ce système. Travaux de recherche financés et réalisés dans le cadre du programme BRGM-TOTAL Source-to-Sink

This is a poster presented at the Community Surface Dynamics Modeling System annual meeting (May 17-21, 2022). Abstract: Passive margin stratigraphy contains time-integrated records of landscapes that have long since vanished. Quantitatively reading the stratigraphic record using coupled landscape evolution and stratigraphic forward models (SFMs) is a promising approach to extracting information about landscape history. However, the most commonly used SFM, which is based on an approximation of local, linear slope-dependent sediment transport, fails to produce diagnostic features of passive margin stratigraphy such as long-distance transport from the continental shelf and slope onto the abyssal plain. There is no consensus about the optimal form of simple SFMs because there has been a lack of direct tests against observed stratigraphy in well constrained test cases. Here we develop a nonlocal, nonlinear one-dimensional SFM that incorporates slope bypass and long-distance sediment transport, both of which have been previously identified as important model components but not thoroughly tested. Our model collapses to the local, linear model under certain parameterizations such that best-fit parameter values can be indicative of optimal model structure. Using seven detailed seismic sections from the South African Margin, we invert the stratigraphic data for best-fit model parameter values and demonstrate that best-fit parameterizations are not compatible with the local, linear diffusion model. Fitting the observed stratigraphy requires parameter values consistent with important contributions from slope bypass and long-distance transport processes. The nonlocal, nonlinear model yields improved fits to the data regardless of whether the model is compared against only the modern bathymetric surface or the full set of seismic reflectors identified in the data. Results suggest that processes of sediment bypass and long-distance transport are required to model realistic passive margin stratigraphy, and are therefore important to consider when inverting the stratigraphic record to infer past perturbations to source regions.

Anorogenic reliefs (plateaus and plains) made up about 70% of the total emerged reliefs on Earth. They are characterized by nearly flat erosional surfaces upstream bounded by escarpments, called pediments/pediplains. Africa’s landforms are constituted by very long (several thousands of kilometers) wavelength relief of broad “basins” (depressions) and swells (Holmes, 1944) possibly controlled by mantle dynamics. This "basin" and swell pattern caused Africa to be consisted of numerous endorheic and exorheic systems. Consequently, the Nile River, the longest river on Earth and main object of this study, crosses today a set of two former endorheic systems (Ugandese and Sudanese “Basins”) and one exorheic system (Egyptian Margin) along its courses to the Mediterranean Sea. Our objective is here to unravel the paleorouting systems of the Nile River through relief growth, tectonic, and climate since the uppermost Cretaceous.Several generations of stepped pediments, proxies of relief growth, were characterized and mapped on DEM and satellite images and dated using their geometrical relationships with dated magmatic rocks. To better constrain periods of relief uplift and the deformation wavelength through time, the stratigraphic record of the sedimentary basins located in between two swells were studied using biostratigraphy and sequence stratigraphy. The originality of the approaches is to integrate data of all the source-to-sink (S2S) systems to produce a coherent scenario of the evolution of the Nile.We proposed the following model for the evolution of the Nile River. First, a main large pediplain is formed during the uppermost Cretaceous (?75-66 Ma), acting as a base of any kind of landforms that would be formed afterwards, bounded westward by the Darfur-Ennedi crest. Second, a major marine flooding during late Paleocene time (58-57 Ma) reached a subtle high bounding northward the endorheic Sudanese “Basin”. Third, Pre-Eonile started to form during the uppermost Eocene (~37 Ma) with a divide limited to the Egyptian Margin. Fourth, the Eonile was incised during late Miocene (~10 Ma) at time of a major uplift at the scale of north-east Africa. Finally, the Nile captured first the Sudanese endorheic system in the Early Pliocene (~4 Ma) and altered the Ugandese one in the Middle-Late Pleistocene (less than 1 Ma).

International audience; High-resolution multichannel seismic reflection data that spans significant parts of the Mozambique margin offshore the Zambezi River permits the study of the Oligocene to present architectural evolution of the Zambezi turbidite system. In this time frame, five major depositional units are recognized that evidence a widespread spatial and temporal occurrence of both turbiditic and contouritic sedimentation. They indicate that the sedimentary regime within the turbidite system changed from dominantly aggradational during the Oligocene to mainly erosional during Miocene to an interplay of erosional and depositional processes during the Plio-Quaternary. Different episodes of incision, linked with the Serpa Pinto, Angoche and Zambezi valleys, are recognized in the upstream portion of the Zambezi Fan and highlight a westward (anticlockwise) shift of feeding axes. The central portion of the Zambezi Valley was affected by a progressive structural doming during the Miocene. The dominance of long-lasting erosional processes generated by the continuous rise of the seabed led to a deep entrenchment of the Zambezi Valley. This tectonically-controlled over-incision is believed to be the cause of the absence of Miocene levees, and has played an important role in the stabilization of the valley at its current position. Finally, our study revealed a quasi-constant development of contourite accumulations since the Late Miocene that occur most often synchronous with turbiditic sedimentation. The present study offers unique insight into the controls and stages of development of one of the largest turbidite systems in the world and demonstrates especially its susceptibility to structural activity.

Foreland basins record the evolution of orogens through sedimentary accumulation and recycling and, as such, represent unique archives of the evolution of orogenic systems. Foreland basins are, however, complex source-to-sink systems responding to the uplift of the mountain range, thrusting, eustasy, climate, and the type of lithologies eroded. The respective contributions of these parameters has been numerically evaluated, the influence of the inherited geometries of the foreland on the sediment routing systems has not yet been investigated.We use a Landscape Evolution Model (FastScape) to explore the effect of varying foreland paleo-topography on its stratigraphic architecture. Models consist of a half mountain range steadily uplifting (0.5 mm/yr) over 25 Myrs. Eroded material is transported and deposited in a foreland domain and a distal open marine domain. We present 4 setups with varying paleo-topographies in the foreland domain: an initial flat foreland at sea level (M1), an elevated flat continental foreland (+300 m, M2), a pre-existing 1 km-deep and 100 km-wide depression at the foot of the growing orogen with either a flat forebulge at sea level (M3) or an elevated forebulge (+300m; M4).Our result show that an elevated foreland domain produces, after 25 Myrs, a thinner foreland basin because the faster and efficient sediment export of sediment out of the foreland to the open marine domain reduces the sedimentary load and, in doing so, the flexure. In contrast, a pre-existing depression at the foot of the range, produces a thicker foreland basin because the additional load filling the initial space increases the flexural response. We show that a pre-existing bathymetry is required to preserve marine deposits in the foreland basin. In our experiments, the landscape after 25 Myrs cannot be used to infer the initial foreland geometry as the initial foreland influences is smoothed out after ~10-15 Myrs. The stratigraphic architectures of the foreland basin are nonetheless different. In addition, we show that emplacement of an alluvial fan at the foot of the range results in a transient drop in erosion rate in the range by locally increasing the base-level (autogenetic feedback).

During the upper Cretaceous the South African Plateau underwent an uneven uplift period that coincided with the onset of a long-term climate cooling. This uplift recorded two pulses, an early pulse during the Turonian that affected the eastern margin and a later pulse occurred during the Campanian affecting the western margin (van der Beek et al., 2002; Braun et al., 2014; Baby et al., 2020). We aim here to determine the response of physical erosion and chemical weathering to this tectonic event, that may have played a role in the long-term climate cooling by promoting silicate weathering and associated atmospheric CO2 drawdown. In this study we targeted the IODP 361 site located in the Cape Basin. We applied a new proxy (DeHf) of chemical weathering intensity based on the coupled Lu-Hf and Sm-Nd isotopic systems in clay fractions of the sediments. This approach is combined with X-ray diffraction analyses to determine the concomitant evolution of clay mineralogical assemblages, which in active tectonic settings can provide insights on the evolution of mechanical erosion.Twenty-two samples were analyzed for Hf-Nd isotopic compositions and 99 samples were analyzed for X-ray diffraction analyses. Clay eNd values remain relatively stable throughout the studied interval, mainly within -8 to -9 e-units, but down to -10 e-units in the Maastrichtian, suggesting a relatively stable source of the sediments. These values are coherent with a sediment source from the Karoo basin and/or the Cape Belt (Dia, 1990; Garzanti et al., 2014). Clay mineral assemblages are dominated by smectite (about 65 to 98%) but show an increase in illite proportions during the Campanian-Maastrichtian, up to about 25%. This increase in primary clay minerals may point to an increase in mechanical erosion, that could be linked to the uplift pulse affecting the western south African margin at that time. DeHf values represent the departure of eHf from the clay array (Bayon et al., 2016), and display a marked increase during the Campanian-Maastrichtian as well, suggesting concomitant enhanced weathering of the nearby margin at that time.Altogether, our data suggest a coupled response of mechanical erosion and chemical weathering of the southwestern African margin during the upper Cretaceous tectonic uplift of the margin, which also may have played as an active CO2 consumption mechanism.

This is a presentation given remotely at the Geological Society of America online annual meeting (October 26-30, 2020). Abstract: Numerical models that explicitly link source to sink (S2S) are critical for inferring past tectonic and climatic perturbations to Earth’s surface from the sedimentary record. While models seeking predictive power must simulate surface processes at both source and sink, substantially more model formulations exist for landscape evolution than for seascape evolution and the building of stratigraphy in marine basins. Most marine sedimentation models operating at basin spatial scales and geologic temporal scales use local linear diffusion approximations for sediment transport. Such approximations produce realistic stratigraphy in shallow marine environments, but do not replicate observed deep marine deposition patterns. Full closure of S2S sediment budgets requires models with predictive power over the development of both shallow and deep marine stratigraphy. We present a new marine sedimentation model that incorporates two simple modifications allowing non-local sediment transport: 1) the possibility of sediment bypass on steep slopes, and 2) long-distance transport, even over near-zero slopes. We constrain, using Bayesian inference techniques, the four model parameters by comparing modeled against observed stratigraphy from 130 Ma of passive margin evolution in the Orange Basin, southern Africa. Best-fit modeled stratigraphy captures the form of the observed record. Best-fit parameter values imply important roles for both model elements we introduced: sediment bypass on steep slopes and long-distance transport over very gentle slopes. We attribute remaining model-data misfit to additional transport processes—hemipelagic sedimentation, grain size variations, or ocean bottom currents—that are not captured by our simple model but might be required to explain sediment runout distances longer than those produced by our best-fit model. Results suggest that predictive modeling of marine sedimentation requires departing from local diffusion approximations, even over ocean-basin-filling timescales. Simple treatment of nonlocal transport dynamics can improve S2S model predictive power, and may enable better recovery of environmental signals from the long-term stratigraphic record.

Oceanic Anoxic Events (OAEs) are short-lived global carbon cycle perturbations characterized by significant changes in the chemistry, temperature and circulation of the oceans of the world. The forcing mechanisms behind these events remain a subject of discussion, especially for the Jurassic and Cretaceous periods. Typically, these events are thought to be triggered by a contemporaneous emplacement of a large igneous province (LIP) associated with a significant release of CO2 into the atmosphere and leading to rapid global warming. In turn, induced sharp climatic change promotes an acceleration of the hydrological cycle which intensifies continental weathering, increases input of nutrients into the oceans and drives elevated rates of primary productivity. Organic productivity increase causes high oxygen demand leading to anoxia accompanied by enhanced carbon burial.The primary carbon source of the Aptian OAE1a, (~120 Ma, D. forbesi, D. deshayesi and D. furcata ammonite zones or G. blowi and L. cabri planktonic foraminiferal zones) is suggested to be the Greater Ontong Java Plateau (G-OJP) which peaks of activity are interpreted to be coeval to specific phases of the global crisis, such as a global biocalcification crisis. It is also known that the GOJP initial emplacement preceded the onset of OAE1a. What remains unclear is therefore what other processes could have triggered the OAE1a and what is the exact timing of its onset. OAEs commonly relate to periods of world scale major marine transgression (eustatic maximum flooding) as a consequence of global warming, potential deglaciation and/or addition of massive volcanogenic rock volume into the ocean. Nevertheless, the relationship of the onset of OAEs with the maximum flooding and the exact position of their time interval with respect to the global eustatic sea-level curve are still ambiguous.This study focuses on the Aptian of the Tethyan margin in Tunisia, which sediment record covers the OAE1a and aims at understanding the exact mechanisms and their interplay in relation to the initiation and onset of this event, with a particular focus on the eustatic factor. The study methods include sedimentology, biostratigraphy, sequence stratigraphy and chemostratigraphy integrated with petroleum exploration well data coupled with published datasets and studies. Emphasis will be given to the reconstruction of the accommodation space with the aid of paleo-bathymetry estimations based on facies sedimentology and benthic foraminifera. At a later stage, the results will be correlated with data from SE Spain and Northern Europe (Greensand facies). One of the main goals of this project is to provide a global assessment and overview of the positioning of the OAE1a in relation to the early Aptian maximum floodings and understand in depth the critical factors, confluences, as well as thresholds that were necessary to be exceeded to trigger this event in a qualitatively and quantitatively manner.The project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No 860383 (https://www.s2s-future.eu/).

International audience; Sediment accumulation rates in foreland basins results from a complex interplay between surface and deep processes in both the exhumed relief domain and sedimentary basins. The growth and decay of a mountain belt during orogenic and post-orogenic phases have been largely studied thanks to thermochronological and structural studies. The sedimentary response of the orogenic phases in the preserved sediments of the surrounding basins is well known in terms of sedimentary filling patterns and architecture, but much less better quantified. Here, we performed a measurement of the siliciclastic sediment volumes of the Pyrenean retro-foreland basin – the Aquitaine Basin and the Bay of Biscay during Cenozoic times – for a better understanding of the erosion and the sediment transfer and deposition during the convergence (syn-orogenic) to post-convergence (post-orogenic) periods of the Pyrenees Mountain. The measurement of the compacted siliciclastic sediment is based on sediment thickness (isopach) maps of known lithologies, derived from the interpretation of 40 000 kms of seismic profiles. Thanks to the siliciclastic sediment volumes quantification and a well-known retro-foreland basin tectono-sedimentary evolution, we bring quantitative results as: (1) The amount of preserved sediments is of 51 500 ± 16 800 km3 for the Cenozoic. (2) The siliciclastic sediment rate curve during Cenozoic shows two major increase around 26.0 Ma and 2.5 Ma. The 26.0 Ma increase is clearly related to the erosion of the Pyrenees of tectonic origin. The major 2.5 Ma one would be mainly related to a climatic forcing. (3) The mass balance between the Aquitaine Platform and the deepest domains change through time in favour of the deep domain. This might be explained by the ratio between subsidence that created accommodation space and the sediments feed by the mountain belt and stored in the Aquitaine Platform.

International audience; Diffusion-based stratigraphic models are widely used to simulate sedimentary systems and margin deltas. Diffusion-based models assume that the topographic evolution primarily depends from its slope. Limited attention has however been given to the calibration of the transport coefficients. Here, we evaluate transport coefficient values from natural examples, the Ogooué and Zambezi rifted margin deltas over the last 5 to 12 Ma respectively. We developed a method to estimate transport coefficients based on high resolution seismic stratigraphy analysis of the stratigraphic architecture of these deltas. For each stratigraphic sequence, we calibrated the sand/shale ratios of the deposits, we restored their depositional slopes, we estimated their uncompacted accumulated volumes and we calculated the transport coefficient (Kd) from the sediment flux / slope ratio.Estimated values of Kd fall within one order of magnitude (x 0.1 km2/ka), a much narrower range than previously published values (x0.0001 to x100 km2/ka). We show that the diffusion approximation is optimal at 10 - 100 km scale and 0.5 - 1 Ma time resolution, independently of the stratigraphic context. We show that the diffusion assumption is appropriate for the formation of the clinoforms (mainly gravity driven). It is however not optimal for the shelf and distal domains where additional processes (e.g. wave, flood, hemipelagic, turbidites, oceanic current), not accounted for it the diffusion assumption, significantly impact sediment transport. We documented a significant increase of Kd values after 0.9 Ma, coeval of an increase in the amplitude of eustatic variations at this time indicating that the calibration of Kd from present day sedimentary systems might not be optimal for simulations of sedimentary systems before the last million years.

Ferruginous duricrust formation takes place by dissolution and accumulation of iron during the wet season and precipitation during the dry season. However, the formation of iron duricrusts has always been the centre of much debate. They commonly form as hard iron layers in tropical and subtropical environments with strong climatic seasonality. They were first described in Africa, Australia and India in the 1950’s. They often cap landscapes, which can be explained by their extremely high iron content making them more resistant to mechanical weathering. However, in recent years, iron duricrusts were also described at depth in the regolith, like in South America.This has led to 2 distinct formation hypotheses: the first one relies on the vertical beating of the water table most likely in a stable environment combined to lateral hydraulic transport of iron. In this scenario, iron hydroxides accumulate in one specific region after being transported from surrounding source areas through the water table, and precipitate as Fe3+ during the dry season. Through time, this leads to duricrusts forming within the water table beating range. This model is compatible with duricrusts forming at depth within the regolith. The second hypothesis relies on the vertical, in situ leaching of elements and resulting compaction and surface lowering. During weathering, iron nodules accumulate with the progressive leaching of soluble elements from the parent rock, leaving only the iron oxides, ultimately forming a duricrust. It implies a genetic link between the duricrust, the lateritic profile and the underlying parent rock. This model explains why duricrusts are mostly observed near the surface. Nevertheless, there is no consensus on the conditions under which either of these hypotheses prevail. To address this issue, we developed two separate first-order numerical models representing the two hypotheses for duricrust formation. We used the models to demonstrate that the hypotheses lead to different scenarios of duricrust formation by running a large number of simulations. Especially, we show that the stability of a landform is a discerning element between the 2 models. In the first case, quiescent periods of time in between uplifting periods are crucial, while in the second case, constant dynamic uplift is needed to enable the accumulation of enough elements by compaction.

Aim Past pollen records reveal the changes in latitudinal distribution of plants in relation to climate, particularly their expansion in response to global warming. The maximum northward expansion of the mangrove genus Avicennia since the Early Eocene is known, but this information is missing for other mangrove taxa. Here, we evaluate the diversity of past mangroves with respect to latitude during three Cenozoic thermal maxima (PETM: 56 Ma; EECO: 54–49 Ma; MMCO: 17–14 Ma). Location North Atlantic, Mediterranean. Taxa Avicennia, other mangrove taxa (Rhizophoraceae, Nypa, Xylocarpus, Pelliciera, etc.). Method We collected well-dated marine sediments along a Northern Hemisphere latitudinal transect and we analysed their pollen content in order to compare the past distribution of mangrove taxa with the present. The analysis of 89 samples (PETM: 13; EECO: 31; MMCO: 45) was performed and interpreted using a robust botanical background for identification of pollen grains and their representativeness in marine sediments. Results During the Early Eocene, two palaeolatitudinal thresholds at 65–70°N and 35°N, respectively, delimited the Avicennia-only mangrove from a diversified but scrawny mangrove and finally from a diversified and well-developed mangrove. The Avicennia threshold was selective at 40°N during the Mid-Miocene. The Avicennia range limit was up to 10–15° poleward of the limit for other mangrove taxa during the Early Eocene and the Mid-Miocene compared with 9° at present. Main conclusions A buffer zone characterised by a diversified but scrawny mangrove co-occurring with a few megathermal plants occurred in the Early Eocene between 35°N and 65–70°N. This finding questions the relative influence of a more ‘equable’ climate and/or the ability of some taxa to expand towards areas with cooler conditions in the past. Mangrove provincialism, which was established progressively after the Early Eocene, was probably forced by plate tectonics. The taxonomic impoverishment of the Atlantic East Pacific province was probably caused by successive periods of global cooling. These results support the Tethyan origin of the mangroves.

International audience; Les connaissances acquises sur l’exhumation de la chaîne pyrénéenne et l’évolution des bassins d’avant-pays adjacents permettent à présent d’appréhender ce système orogénique complexe dans une démarche intégrative dans l’espace et le temps. Cette approche, dite « source-to-sink » s’attache à comprendre l’évolution du routage sédimentaire depuis la Source (relief orogénique, craton, recyclage de bassin) en passant par la zone de transfert (périphériques ou internes au bassin) jusqu’au réservoir final (bassin flexural, bassin turbiditique profond). Nous proposons, dans le cadre de cette nouvelle cartographie, de compiler les données disponibles et nouvellement acquises dans le projet S2S, sur l’ensemble du domaine péri-pyrénéen du Golfe du Lion à l’Est jusqu’au Golfe de Gascogne à l’Ouest en incluant le Massif armoricain au Nord jusqu’au bassin de Madrid au Sud. La réalisation de ces cartes s’appuie sur l’utilisation de nombreuses méthodes et outils, tels que les reconstructions cinématiques du système Ibérie-Europe-Méditerranée, les coupes restaurées, l’histoire d’exhumation par thermochronologie, le traçage des sources, la caractérisation des surfaces d’altération et d’érosion, la synthèse de l’activité des accidents structuraux majeurs, les reconstructions paléogéographiques, l’analyse des géométries sédimentaires et des directions de transport ainsi que la quantification des volumes préservés dans les bassins. Les pas de temps choisis pour ces cartes permettent de rendre compte de différents stades d’évolution tectono-sédimentaire du système péri-pyrénéen au stade précoce de l’orogénèse - (1) à 52 Ma, Yprésien, aux stades d’orogenèse mature - (2) à 40 Ma, Bartonien et (3) à 34 Ma, Priabonien ainsi qu’aux périodes post-orogénique - (4) à 24 Ma, Chattien et (5) à 11 Ma, Tortonien. Les compilations effectuées mettent en regard domaines exhumés et zone de sédimentation en termes de flux et de volumes, et permettent de cartographier les systèmes de routage et leur évolution au cours d’un cycle de construction/destruction d’un orogène.Travaux de recherche financés et réalisés dans le cadre du programme BRGM-TOTAL Sourceto- Sink