High-Resolution Detrital Zircon Geo- and Thermochronometry of the Eocene Ainsa Basin, South Central Pyrenees, Spain

Abstract:

Foreland basin deposits in the South Central Pyrenees provide a natural laboratory for investigating the interplay between tectonic and sedimentary processes. Early Cenozoic foreland basin deposits preserve the record of hinterland erosion throughout Pyrenean collision. This study uses high-resolution detrital zircon (DZ) geo- and thermochronometry to investigate the progressive evolution of sediment provenance and paleodrainages through the stratigraphic record and across different depozones of the foreland basin. The Ainsa Basin in the South Central Pyrenees contains a secession of Eocene turbidite packages sampled in detail to examine the transition from fluvial to shelf-slope to deep marine environments. New data are congruent with previous DZ studies showing the turbidites are mixed from two main sources, Hercynian plutons from the Pyrenean axial zone and Cadomian/Caledonian plutonic and metamorphic rocks exposed in the Eastern Pyrenees. Although many of the turbidite packages yield similar DZ U-Pb signatures, detailed DZ U-Pb-He double dating resolves subtle differences between stratigraphic packages. These differences likely reflect varying degrees of mixing of multiple sources, or autogenic sorting during transport. Some units yield anomalous DZ U-Pb distributions, which potentially indicate an additional source region. Studying these anomalies will better our understanding of processes such as sediment bypass in marine canyons and fluvio-deltaic depozones as well as axial vs transverse paleodrainages. Also these anomalous signals can be traced throughout depozones in the basin and used to refine stratigraphic correlations between different parts of the basin. The data, Interpreted in the context of the structural and stratigraphic framework of the Pyrenean foreland basin, provide insights into processes during sediment delivery, paleodrainage networks, and the interplay between tectonic deformation and basin sedimentation.