Dolomite-Rich Condensed Sections in Overbank Deposits of Turbidite Channels: The Eocene Hecho Group, South-Central Pyrenees, Spain
Résumé
In the Eocene turbidite systems of the south-central Pyrenees, high-resolution correlations within the apparently monotonous successions of thin beds of the major channel-overbank deposits have been facilitated by the occurrence of decimetre-thick, yellowish beds of micritic limestones and marlstones, which thus serve as marker beds. These yellow beds (YB) occur after deposition of a sandy stage of growth at turbidite system scale but can be only recognized in the overbank deposits of major turbidite channel complexes. Whole-rock and fine-fraction X-ray diffraction (XRD) analysis indicate that most YB contain detrital clay and consistently high concentrations of Fe, Mn and P, which are ascribed to condensation-driven, redox elemental redistribution. The YB are also richer in dolomite and calcite than the adjacent claystones, what is attributed to colonization by cryptobacteria algae. Dolomite has a more radiogenic 87Sr/86Sr signature than ambient sea water, suggesting partial derivation of Sr from detrital aluminosilicates.