Paleoenvironmental changes across the Paleocene\u2013Eocene boundary in West Central Sinai, Egypt: geochemical proxies

Abstract

A geochemical analysis has been conducted on twenty-six sediment samples spanning the P–E boundary interval collected from the Esna Shale in three well-dated stratigraphic sections in west-central Sinai, Egypt to interpret paleoenvironmental changes associated with the P–E boundary events. The Esna Shale consists of hemipelagic marine shales and marls and it is subdivided stratigraphically into the uppermost Paleocene Hanadi Member unconformably overlain by the lowermost Eocene Dababiya Quarry Bed (DQB) and El-Mahmiya members. A variety of geochemical proxies including the Al-normalized elemental concentrations and redox-related elemental ratios and parameter (V/Cr, V/V + Ni and Mn*) and productivity indicators (Porg and Babio) were employed for paleoceanographic interpretations. Across the P–E transition, the concentrations of SiO2, TiO2, Al2O3 Fe2O3, MgO, V, Cr, Ni, Cu, Rb, and Zr notably increased, whereas the concentrations of CaO, MnO, Sr, and Zn abruptly decreased. The variation in the elemental concentrations is attributed to the carbonate dissolution because of increased ocean acidification as well as a brief increase in the detrital influx associated with the brief humid interval at the base of the Eocene. The Al-normalized detrital-related elements (Ti, Zr, and Rb) values show a relatively homogeneous profile suggesting a uniform detrital input from an unchanged source rock. The simultaneous significant increase in the V/Cr and V/V + Ni ratios and enrichment of Ni, Cu, and Zn in the sediments of the DQB suggest that the depositional basin experienced dysoxic to slightly anoxic bottom conditions. The coeval increase in the Porg and Babio in the sediments of the DQB suggests an increase in nutrients availability and consequently primary productivity possibly due to enhanced upwelling during early Eocene.