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On multi-millennial scales, sedimentary systems can be disturbed by external forcings such as tectonic uplift and climate change. These environmental changes affect sediment fluxes and sediment composition from the zone sediments are produced to their deposition zone. Although we have a good understanding of how sedimentary systems react to forcings such as sea-level change, tectonic uplift or global warmings, major challenges remain concerning the record and unravelling of these signals in past sedimentary archives. These archives may hold key information for predictive models concerning actual and future environmental problems. To better understand how tectonic and climatic signals are recorded and are reflected in past sedimentary successions, an Eocene (33-56 Ma) sedimentary system in the south Pyrenean foreland basin was studied during a time-period rich in tectonic and climatic events.

Understanding the origin of stratigraphic cycles preserved in sedimentary successions is one of the main goals of sequence stratigraphy. Cyclicities in sediments are controlled by local and regional tectonics, global sea level and eustatic variations themselves linked to climate and global tectonics, as well as sediment supply also related to tectonics and climate. The Ainsa foreland basin (southern central Pyrenees, Spain), is composed of very well preserved syn-tectonic deep marine deposits in which stratigraphic cycles are characterized by an alternance of hemipelagic intervals and sediment gravity flow (SGF) deposits. The origin of stratigraphic cyclicity in the Ainsa basin has been largely discussed, however the absence of accurate chronostratigraphic constraints on the sandy systems of the basin remains one of the main issues to tie these pulses of coarse sediments with external factors. In this work, two age models were developed based both on new magnetostratigraphic data and stable isotope stratigraphy. New carbone and oxygen isotope data for the upper Hecho group were compiled with existing isotope profile of the lower Hecho group to provide a complete record for the entire deepwater succession of the Ainsa basin. The first age model considers continuous depositions in the basin and places our magnetostratigraphic results in the light of existing paleomagnetic studies previously performed in the Ainsa basin (Bentham and Burbank, 1996 ; Mochales et al., 2012a). It provides new time lines for the basin in agreement with the age model currently accepted for the South Pyrenean foreland basin. In the second age model, we used stable isotope signal combined with published large foraminifer biostratigraphic constraints (Scotchman et al., 2014). The obtained stable isotope curves show significant similarities with global isotopic records, with in particular a negative oxygen excursion towards the top of the succession that could be attributed to the Mid-Eocene Climatic Optimum. This age model is thus controversial as it is in significant disagreement with previous age models developed in the area and implies several important hiatuses in the slope depositional environments of Ainsa turbiditic series. In this presentation, we will discuss the two ages models and their implications for mountain building processes in the Pyrenees. Finally, we will use them to compare the stratigraphic record of the basin with sea-level fluctuations and discuss the possible primary drivers of stratigraphic signals.

Among the most urgent challenges in future climate change scenarios is accurately predicting the magnitude at which precipitation extremes will intensify. Analogous changes have been reported for an episode of millennial scale 5°C warming termed the Palaeocene-Eocene Thermal Maximum (PETM; 56 Ma), providing independent constraints on hydrological response to global warming. However, quantifying hydrologic extremes during geologic global warming analogs has proven difficult. Here we show that water discharge increased by at least 1.35 and potentially up to 14 times during the PETM in northern Spain. We base these estimates on analyses of channel dimensions, sediment grain size, and palaeochannel gradients across the onset of the PETM, which is regionally marked by an abrupt transition from overbank palaeosol deposits to conglomeratic fluvial sequences. We infer that extreme floods and channel mobility quickly denuded surrounding soil-mantled landscapes, plausibly enhanced by regional vegetation decline, and exported enormous quantities of terrigenous material towards the ocean. These results support hypotheses that extreme rainfall events and associated risks of flooding increase with global warming at similar, but potentially at much higher, magnitudes than currently predicted.

Continental to marine correlations have always been a challenge regarding to sequence stratigraphy. The longstanding debate is about how surfaces and sedimentary packages translate from one environement to another and the various origins that have been put forward to explain them : eustastic sea level changes, sediment supply variations, subsidence pulses or tectonic variations. In the deep water system of the lower-middle Eocene Ainsa basin, in the southern Pyrenees (Spain), as well as in its fluvial counterparts in the Tremp- Graus basin, stratigraphic cyclicity in the form of repetitive packages of sand and shale alternations of intermediate timescales (10^4 to 10^6 years) has long been recognized and has typically been imputed to eustatic changes, with a modulation by active tectonics. Most of the studies have so far focused either on the deep water system or on their fluvial counterparts without a detailed effort at the correlation between both. Our objective is to evaluate the role of eustatic variations, that are well known to have taken place at these periods, in generating or modifying such cyclicities and to understand the link, at high resolution, between the continental and marine deposits. This is particularly important in order to understand how sea-level fluctuations are tided to depositional environments over multi-millennial times-scales and how the deep- sea sedimentary record can be used to reconstruct the Earth's history of surface response to climate change. To address these issues, a mapping and multi-proxy approach was undertaken in the Tremp-Graus and Ainsa basins. We focus on the middle Eocene Castissent formation, a major fluvial excursion and its deep marine time-equivalent; the turbiditie systems of Fosado, Arro and Gerbe. Through a study of carbon and oxygen stable isotopes on the bulk rock and on the organic matter, geochemistry of major and trace elements performed on two sections representing the distal marine and the continental part of the basin, we attempt to trace environmental signals across the whole source-to- sink system. These analyses coupled with thorough physical mapping on the field allow us to discuss hypotheses on the timing of deposition of the different continental sedimentary packages with repect to the marine ones.