Tectono-stratigraphic evolution of deep-marine clastic systems in the Eocene Ainsa and Jaca basins, Spanish Pyrenees: Petrographic and geochemical constraints.

The Early-Middle Eocene deep-marine siliciclastic systems of the Ainsa and Jaca foreland basins, Spanish Pyrenees, have been used to develop and support generic models for deep-marine deposits, from process-based to system-based perspectives, and these ideas have been applied globally by academics and industry alike. Despite the considerable amount of research into many aspects of sedimentology of the Ainsa and Jaca basins, the widely-adopted stratigraphic correlation of sandstone systems in the Ainsa and Jaca basins is very poorly-constrained, although the stratigraphy and accurate correlation of sandstone bodies along the basin are paramount to any depositional models that arise from any studies in the Ainsa and Jaca basins. This study used petrography, geochronology, major and trace element geochemistry to better constrain and understand the evolution of the basinal sediments and fingerprint the sandstone bodies within the Ainsa-Jaca basin as a means of correlation. An additional pilot study was carried out on carbon and oxygen isotopic signatures of larger foraminifera from the outcrops. Three discrete sediment sources are recognised for the deep-marine Early to Mid-Eocene sandstone bodies in the Ainsa and Jaca basins. The arenite composition in the Ainsa and Jaca basins is interpreted to be mainly controlled by synsedimentary tectonic processes that led to changes in sediment sources during basin evolution. Comprehensive petrography data shows that each system of the Ainsa and Jaca basins has a characteristic petrofacies. Three main petrofacies are recognised and on the basis of these petrofacies, a revised correlation of the sandy systems is proposed between the more proximal Ainsa basin, and the more distal Jaca basin sediments, now separated by the Boltana anticline, across which it is impossible to actually trace out individual beds or sandstone packages between both basins. The new correlation scheme, along with the newly identified sediment provenances, changes the current (published) understanding of the Ainsa and Jaca basins evolution and palaeogeography