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We present evidence of a ca 200 m-thick Paleocene–Eocene Thermal Maximum (PETM) sedimentary section within a 543 m-thick deep-marine core in the Gulf of Mexico (GoM). The negative carbon isotope excursion (CIE) characteristic of the PETM is identified thanks to organic carbon stable isotopes and tightly linked to the Paleocene-Eocene boundary thanks to high-resolution biostratigraphic constraints provided by nannofossil and palynomorph assemblages. The unusual thickness of the CIE suggests that the PETM climate perturbation in the upstream North American catchments induced a substantial response in the downstream sectors of the Gulf Coastal Plain, and ultimately in the GoM. This relationship is illustrated in the deep-water basin by 1) the deposition of a shale interval when coarse-grained terrigenous material was trapped upstream at the onset of the PETM, and 2) considerable sediment supply in response to increased sediment transport upstream. These results are particularly relevant for paleoclimate and source-to-sink reconstructions because they link deep water sedimentation with a continental-scale paleo-drainage.

Ancient fluvial deposits typically display repetitive changes in their depositional architecture such as alternating intervals of coarse-grained highly amalgamated (HA), laterally-stacked, channel bodies, and finer-grained less amalgamated (LA), vertically-stacked, channels encased in floodplain deposits. Such patterns are usually ascribed to slower, respectively higher, rates of base level rise (accommodation). However, “upstream” factors such as water discharge and sediment flux also play a potential role in determining stratigraphic architecture, yet this possibility has never been tested despite the recent advances in the field of palaeohydraulic reconstructions from fluvial accumulations. Here, we chronicle riverbed gradient evolution within three Middle Eocene (~ 40 Ma) fluvial HA-LA sequences in the Escanilla Formation in the south-Pyrenean foreland basin. This work documents, for the first time in a fossil fluvial system, how the ancient riverbed systematically evolved from lower slopes in coarser-grained HA intervals, and higher slopes in finer-grained LA intervals, suggesting that bed slope changes were determined primarily by climate-controlled water discharge variations rather than base level changes as often hypothesized. This highlights the important connection between climate and landscape evolution and has fundamental implications for our ability to reconstruct ancient hydroclimates from the interpretation of fluvial sedimentary sequences.

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

The knowledge acquired on the exhumation of the Pyrenean mountain belt and the evolution of the adjacent foreland basins makes this Alpine-type domain a good laboratory to better constrain a full sediment routing system in a compressive context and to apprehend the driving processes controlling the sediment routing in space and time. This integrated approach aims at enhancing our basin mastering approach as well as improving our predictions of reservoir properties.This Source-to-Sink study seeks to understand the evolution of sedimentary routing from the Source (orogenic relief, craton, basin recycling) through the transfer zone (peripheral or internal to the basin) to the final sink (flexural basin, deep turbiditic margin). Within this new cartography, we propose to compile the data over the entire peri-Pyrenean domain. We produced large scale quantitative and qualitative maps to better observe and interpret the tectonic, climatic and surface processes impacts of the SRS behavior.These maps include kinematic reconstructions of the Iberian-European-Mediterranean system, restored sequential cross-sections, history/magnitude of exhumation by thermochronology, source tracking, characterization of weathering and erosion surfaces, synthesis of the major structures activity, paleogeographic reconstructions, analysis of sedimentary geometries and transport directions as well as the quantification of volumes preserved in the basins. Their interpretation is combined with a time representation along the routing system, linking classical basin wheeler diagram representation to source erosion and lithologies to obtain a continuous view on the sediment journey.The time steps chosen for these 5 maps account for the different stages of tectono-sedimentary evolution of the peri-Pyrenean system at the early-, syn- and post-orogenic stages. The compilations carried out compare exhumed domains and sedimentation zones in terms of fluxes and volumes and make it possible to map the routing systems and point out the main drivers for the surface evolution during the construction/destruction cycle of an orogen. This research work was financed and carried out as part of the BRGM-TOTAL Source-to-Sink program

The topographic history of an orogen results from the interactions of climate and tectonics, and it can be reconstructed from the sedimentary record of its peripheral basins. Previous tectonostratigraphic studies, including flexural models, and sparse stable oxygen and carbon isotope data from the South-Pyrenean foreland basin suggest that a major period of topographic growth occurred in the late Paleocene-early Eocene. To further test this hypothesis, we present a stack of 658 stable isotope measurements on whole-rock marine carbonate mudstone from a 4800-m-thick composite sedimentary succession which provides a 12 Ma continuous record of environmental conditions during the early to middle Eocene (54 to 42 Ma). From the base of this record (at 54 Ma), oxygen isotopes (δ18O values) show a faster decrease rate than the coeval global negative excursion associated with the Early Eocene Climatic Optimum (EECO). This local alteration of the global δ18O signal indicates that topographic growth during this period, associated with significant tectonic activity, perturbed the oxygen isotopic composition of foreland waters. Thus, our data suggest that significant topographic uplift of the Pyrenean orogen started from at least 54 Ma and continued until ca. 49 Ma, reaching the maximum elevations of 2000±500m in this phase from previous isotope and flexural studies. In addition, our record shows that the long-term carbon stable isotope composition during this period remained relatively stable with no similarity to the global bell-shaped long-term trend of the EECO. This is consistent with the restricted physiography of the South-Pyrenean foreland basin, mainly influenced by local sedimentary and water inputs. Overall, the Pyrenean topographic growth from the Late Cretaceous to the Miocene displays several growth stages that seem to be primarily determined by episodes of an increased rate of tectonic plate convergence. The duration of these growth stages (several millions of years) is possible documentation of the response time of mountain ranges to tectonic perturbations. The results of this work, therefore, demonstrate that stable isotope measurements on whole-rock sediments in foreland basins can provide key information for tectono-climatic and topographic reconstructions of mountain ranges.

Studies have long recognised the role of upstream factors such as sediment flux and water discharge variations in determining the equilibrium river profile. This approach has, however, not been tested in the stratigraphic record of ancient fluvial systems. Here we test the hypothesis that upstream factors control fluvial architecture through changes in water discharge and sediment flux. For this purpose, we utilise the Escanilla sediment routing system, an extensively documented source-to-sink river system in the southern Pyrenees, Spain, and of middle-upper Eocene age (ca. 40 Ma). Our focus is on the locality of Olson, at the distal part of the system, where the gullied landscape allows detailed documentation of fluvial stratigraphic architecture. We describe several fining-upward sequences of 35–40-metre thicknesses with a laterally extensive, amalgamated base overlain by a floodplain-dominated interval containing isolated channel bodies. For each amalgamated and non-amalgamated interval, data pertaining to grain size distributions and flow depths were collected. These data sets were used to perform quantitative palaeohydrological analysis based on paleoslope reconstruction, and from this, we estimated palaeoflow velocity, unit and total discharge, and bedload sediment fluxes. We find that the river slope is lower in the amalgamated intervals as discharge and sediment flux increases, while river slope increases in the non-amalgamated interval as the discharge and flux decreases. Given the available magnetostratigraphic constraints, the studied interval is compared to an astronomical reference curve. The depositional sequences reflecting variations in discharge are likely paced by the major component (413 000 yrs) of the Earth orbital eccentricity variations and thus point to climatic effect on sediment production and transport as the main driver of the fluvial sequences rather than autogenic shifts of the distributive fluvial system, or base-level changes.

Allogenic factors such as climate and tectonics are regulating the mechanisms involved in sediment generation, transport and deposition. A key challenge for modern society is to predict and better understand how sedimentary systems adapt to an abrupt change in climate. The geological record allows an insight on past climate crises and their registration in sediments.This study focuses on the changes in physical sedimentary processes during the Paleocene-Eocene Thermal Maximum (PETM, 56 Myrs ago) in the Southern Pyrenees (Spain). A lengthening of the siliciclastic system has been shown to occur coevally to the PETM. Yet, connections throughout the sedimentary system from source to sink and reconstructions of the processes involved in this short-term lengthening lack constraints. Although higher seasonality in pluviometry is usually invoked to explain the increase in sedimentary export, this hypothesis is based on very few continental outcrops only and do not include any system-scale quantification. Here we propose to test this hydrology-based hypothesis thanks to (i) a better understanding of the source-to-sink system’s paleogeography, (ii) paleohydraulic quantifications applied on supplementary outcrops and (iii) grain-size used as a down-system common thread.First, the sources are better constrained thanks to provenance analyses combining petrography and double dating on detrital zircons (U/Pb and (U-Th)/He). Then, reconstructions of paleohydraulics in several continental outcrops allow to compare paleoslopes and water discharges between pre- and syn-PETM deposits. Finally, studying grain-size along the whole system allows a quantitative estimation of the climate-related evolution of the system’s diffusivity.This system-scale study provides quantitative insights on the changes in sediment transport processes during an abrupt climate change. The deduced landscape evolution is then a valuable tool to be applied on today’s systems. This research is carried out in the scope of the lead author’s PhD project and is part of the S2S-FUTURE European Marie Skłodowska-Curie ITN.

We aim to determine the intensity of chemical weathering of detrital clays, as well as the lag time between the onset of the Paleocene-Eocene Thermal Maximum (PETM) and the chemical weathering response in a source-to-sink system. The PETM was a hyperthermal event characterized by an abrupt increase in global temperature (5–8 °C) over a short period (20 ka). A negative carbon isotope excursion marks the onset of the PETM, which reflects the fast injection of light carbon into the ocean-atmosphere system, triggering global climatic changes. Thus, physical and chemical erosion acted as feedback mechanisms to recover the global climate to pre-onset conditions. We focus on the continental section of the source-to-sink system, near the locality of Esplugafreda in the Southern Pyrenean foreland basin. We analyzed the evolution of the clay mineral assemblages in two clay-sized fractions (18O excursion at the onset and body of the PETM found in both size fractions. Further, we combine hafnium and neodymium isotope analyses of both clay fractions to track the silicate weathering intensity. This method will help us constrain the weathering regime and its response time relative to the onset and the body of the PETM. The results obtained in this project will serve to test numerical models of landscape evolution incorporating the chemical weathering response to climatic changes. This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 860383.

Can river management practices impact the grain size patterns along mountain streams? If yes, such practices may have important consequences for the gravel industry, fluvial ecosystems and for the interpretation of grain size patterns in geosciences. Since the motion of particles in a riverbed is dependent on the applied shear stress, which in turn depends on river slope and depth, there are reasons to expect some impact on the riverbed grain sizes after a river channelization or construction of check dams. With the aim to answer the presented question we analyse and compare a large dataset of grain sizes and slopes of exposed gravel bars obtained in two mountain streams, i.e. Sense and Gürbe Rivers. While the Sense River is maintained in its natural character, the Gürbe River has been engineered with more than 60 check dams along c. 5 km on its sediment supply area. Both rivers are situated at the northern border of the Swiss Alps, they share the same source area and experience identical hydroclimatic conditions. In addition, for both streams, landslides and high-concentration flows from steep tributaries supply the clastic material to the trunk. Field work in the Sense River has been carried out c. 8 km downstream of the main sediment supply area, and the corresponding catchment area is c. 120 km2 large. The selected stretch of interest on the Gürbe River lies above an alluvial fan situated right downstream of the supply area. The corresponding size of the drainage area in the Gürber River is c. 12 km2. We collected more than 15’000 grain sizes by applying the Wolman’s pebble count method conducted on orthoimages of exposed gravel bars. The orthoimages were generated from digital photos that were taken by an unmanned aerial vehicle (UAV) and processed with standard photogrammetric techniques. These photos were also used to create digital elevation models, which allowed us to calculate the surface slope at various scales. Despite the differences in catchment area and distance from the supply area, the results from both rivers reveal similar bar-scale slopes (2.0 ± 0.1 cm/m) and grain size D50 (4.2 ± 0.1 cm) and D84 (12.7 ± 0.7 cm) percentiles. Additionally, by calculating the slope around each grain within a 2 m diameter circle, called here « local slope », we found a linear dependence between the local slopes (0.5 to 20 cm/m) and the grain size percentiles in both rivers. Since the check dams are built to reduce the mass fluxes, we consider that the grain size data of the Gürbe River reflects a greater attenuation of the landslide signals than the Sense River data. Furthermore, we suggest that the local slope dependency of the grain size percentiles rather reflects the effects of hydrodynamic processes than those of hillslope processes as controls on the motion of the riverbed particles. It thus appears that the check dams can have an impact on the sediment routing as they attenuate signals related to mass movements.

National audience; La réinterprétation des données de sub-surface dans le bassin d’Aquitaine et les travaux menéssur les Corbières où affleurent le piémont pyrénéen permettent de reconstituer la déformationde ce retroforeland et l’évolution du système source to sink au cours de la période synorogénique,Eocène.Après une phase de quiescence paléocène, l’activité tectonique est marquée dans le bassin par(1) une reprise de subsidence à la fin du Thanétien, (2) la mise en place d’un bassin flexural(Yprésien- Lutétien), contemporain de l’augmentation de la taille de la chaine, et (3) lasegmentation de ce bassin par la réactivation d’accidents hérités à partir du Bartonien, quicorrespond à la collision sensu stricto. A ces trois phases, correspondent des systèmes source tosink différents, et permettent de préciser la compréhension des stades classiques (underfilled,filled, overfilled).1- Le Paléocène (quiescence) enregistre une sédimentation carbonatée qui évolue depuisdes systèmes récifaux vers des systèmes de rampes carbonatées. Durant le Thanétiensupérieur (début de la période syn-orogénique), se mettent en place des systèmesturbiditiques mixte terrigène-carbonaté, alimentés par le Massif Central etvraisemblablement par les premiers reliefs pyrénéens orientaux.2- L’Yprésien (orogenèse précoce) correspond à la croissance progressive des reliefspyrénéens, et une augmentation des apports pyrénéens. Un remplissage rapide duretroforeland par des dépôts deltaïques a lieu. Les influences respectives desévènements climatiques du début de l’Yprésien et de la déformation de l’avant-pays surles volumes érodés et les architectures sédimentaires seront discuses. Le comblementprogressif du bassin génère une large zone de transfert à partir du Lutétien.3- Le Bartonien (collision) correspond à une exhumation importante de la chaine. Dans lebassin d’Aquitaine, l’inversion des structures héritées génère la mise en place demultiples dépôt-centres plus ou moins déconnectés. Il en résulte une modificationmajeure du système source to sink, dans lequel l’augmentation des apportssédimentaires se traduit par un très faible export vers le bassin profond et uneaggradation importante des piémonts.

Fold belts are generally considered as the result of thrusting and folding of a sedimentary cover over a weak decollement layer. As the resulting anticlines are typically spaced in a fairly regular manner, it is tempting to use this spacing along with other geological constraints to obtain insights in the dynamics and rheology of the crust on geological time scales. Here we use the Zagros Mountains as a case study as it is one of the most spectacular, well-studied thin-skinned fold-and-thrust belts in the world (e.g., Stocklin 1968; Mouthereau et al., 2007). Geologically, the Zagros consists of crustal-scale folds with an average spacing of around 14 km, which have been formed in around 5.5 Myrs.