Using U-Pb Detrital Zircon to Identify Evolution of Sediment Drainage in the South Central Pyrenean Foreland Basin, Spain

Abstract:

Late Cretaceous to Oligocene deposits of the foreland basin of the South Central Pyrenees provide a record of the uplift and erosion of the Pyrenean Orogeny and spatial and temporal changes in depositional environments related to the structural evolution of the basin. A significant part of the stratigraphic record is preserved across multiple segments of the depositional profile providing an opportunity for the study of sedimentary systems from source to sink.

In this study, U-Pb radioisotope analyses of detrital zircon grains from Eocene sandstones of different ages and sedimentary environments were used to determine sediment source, timing of sediment input, and distribution across the foreland basin fill. The dominate age population is 270-360 Ma and likely reflects Hercynian granitic sources located in the axial zone of the Pyrenees. Most samples have a secondary age population corresponding to the Cadomian Orogeny rocks currently exposed in the eastern Pyrenees. We can identify two statistically significant suites of detrital zircon age populations: one with a mixed range of ages; and one with a dominance of Hercynian ages. The mixed suite is present throughout the stratigraphic sections studied, and is interpreted to represent the mixing of different aged sediment source rocks and the recycling of older sediments that persisted throughout much of the basin fill. The Hercynian-rich samples occur late in the stratigraphic succession, but occur temporally and spatially with the mixed suite. These are interpreted to represent higher influxes of sediment from the erosion of localized plutons in a smaller catchment area.

Detrital zircon signatures observed in these samples provide an opportunity to link foreland basin sedimentary fill to sources in the hinterland, delineate potential drainage systems, and resolve episodes of uplift and exhumation in the Pyrenees. Sediment signal fingerprinting and propagation is further enhanced using U-Pb age depth-profiling of detrital zircon grains. This approach allowed for resolution of polyphase zircon growth, which can be highly distinctive of potential sediment sources. Integrating these results with the stratigraphic and structural framework of the basin refines our understanding of the controls on sediment delivery and their impact in the stratigraphic record.