Geochemical Evidence for Photic Zone Euxinia During Greenhouse Climate in the Tethys Sea, Egypt

Upper cretaceous organic-rich sediments are good archives for the paleoceanographic changes. Here, a comprehensive set of geochemical, biological, and mineralogical data have been applied in order to evaluate the role of euxinia on the organic matter during deposition. The total organic matter of these organic-rich sediments reaches up to 23 wt%. They have significant concentrations of redox-sensitive trace elements such as Mo, Cu, Zn, Ni, Cd, U, and V. The values of redox proxies (e.g., U/Mo, V/(V + Ni), V/Ni, Ni/Co, V/Cr, U/Th, U authigenic) and the size of framboids pyrite suggest that the Upper Cretaceous organic-rich sediments were deposited under a euxinic water column environment. The molecular fossils data also point to the predominance of the sulfidic anoxic conditions during deposition. The good correlation between TOC and redox proxies indicates that the oxygen-depleted conditions play a significant role in the preservation of that organic matter.