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Controls on Sediment Delivery to the Deep-Water in Eocene Source-to-Sink Clastic Systems of the South Pyrenean Foreland Basin, Spain

Abstract

Eocene-aged depositional systems preserved in the south Pyrenean foreland basin offer a rare opportunity to study contemporaneous stratigraphic record of sedimentary systems from alluvial fans to deep-water lobes. The shelf, slope and basin floor source-to-sink segments of these sedimentary systems are correlative between the basins of Tremp, Ainsa and Jaca. Parts of these sedimentary systems are very well understood from extensive studies on the stratigraphy and tectonics of the basin. However, gaps remain in our understanding of detailed stratigraphic correlations between the different basins, and of the processes that control sediment transfer from one sector to the next. Here we present results of an integrated study to investigate the controls on source-to-sink stratigraphy in this basin. Extensive and detailed field mapping, particularly focused on the segment boundaries, has resulted in revised correlations across the basin. Double-dating detrital zircons for both their crystallization age (using U-Pb geochronology) and cooling age (using (U-Th)/He thermochronology) has enabled constraints on the catchment area size and evolution, and how drainage relates to the tectonic growth of the Pyrenees. Carbon isotope geochemistry has been used to invoke climate signals preserved in the stratigraphic record, and investigate the link between climatic variation and the timing of sedimentation from shelf to deep-water. Integrating these results has allowed us to develop paleogeographic models of the sedimentary systems evolution in response to different allogenic controls. These models show the importance of hinterland tectonics in controlling the volume of coarse-sediment delivered to the basin. Eustatic sea-level fluctuations, although of relatively low amplitude during the Eocene, still appear to be critical in the timing of sediment delivery from the shelf-edge to the deep-water basin. Intra-basin tectonics play an important role in controlling accommodation space and setting up gradients that facilitate the transmittal of sediment from shelf to basin via shelf-edge failures and erosional canyon conduits. The models and insights developed from the study of this well constrained basin can be applied to the exploration for reservoir deposits in other basins. This study also demonstrates the value of integrating different analytical methods to de-convolve controls on sedimentation and how this can be used to make predictions up or down the sedimentary profile.