Understanding the Evolution of Clastic Sediments from the Deep-Marine Ainsa-Jaca Basin, Spanish Pyrenees: A Petrographic Approach

Das Gupta, Kanchan¹, Kevin T. Pickering¹ (1) University College London, London, United Kingdom

The Paleogene collision of the Iberian and European plates created a compact two-sided orogen, with paired fold-and-thrust belts and foreland basins north and south of the Axial Zone in the Pyrenees. The Middle Eocene South Pyrenean foreland basin evolved with mainly non-marine/marginal marine environments in the eastern sectors, whilst further west, in the Ainsa-Jaca basin, there was an overall change from fluvio-deltaic to deep-marine systems.

The Ainsa-Jaca basin comprise ~10-12 million years of deposition of deep-marine clastics with a cumulative thickness of ~4 km and provide an ideal natural laboratory for studying slope-basin depositional systems. The Ainsa basin contains about 20-25 deep-water sandbodies, typically 10s m thick but packaged essentially as 7 coarse clastic depositional complexes, each in the order of at least 100-300 m thick. This study fingerprints the sandbodies within the Ainsa-Jaca basin as a means of correlation, in order to better constrain and understand the evolution of the basinal sediments.

223 sandstone (arenites) samples, fine to coarse grained, were collected from outcrops spreading throughout the Ainsa-Jaca basin, and they quantitatively analysed for their mineralogical and textural composition in thin section. Different compositional (petrographic) trends and petrofacies are identified. The composition of sandstones permits the characterization of each depositional complex in terms of both constituents and provenance. Arenite composition in the Ainsa basin is found to be mainly controlled by syn-sedimentary tectonism. There is a temporal change of sediment provenance as the basin evolved.