Paleoredox conditions and paleoproductivity of the early-Eocene sediments in the Gaga Section, Western Desert, Egypt

Abstract

The release of massive amounts of greenhouse gases, mainly carbon dioxide and methane, into the atmosphere was assumed to have generated anoxic conditions during the Paleocene-Eocene Thermal Maximum (PETM). These gases caused the globe to warm rapidly and significantly, disrupting ocean circulation patterns and reducing the quantity of oxygen accessible to marine organisms. Herein, detailed geochemical investigations were performed on forty-one cutting samples collected from the Gaga section (Egypt), with an emphasis on total organic carbon (TOC), trace elements, and carbonate content. These geochemical observations revealed important information about paleoredox conditions, marine biological productivity, and processes controlling organic matter accumulation. A sudden decrease in carbonate contents, as well as the scarcity of nannofossils, indicate the severity of the acidification during the onset of the PETM. Abundant framboidal pyrite within foraminiferal shells at the PETM interval indicates the occurrence of sulfur-related processes during diagenesis, a consequence of organic matter decomposition under oxygen-depleted conditions where sulfur-reducing bacteria play a significant role. The ratios of V/(V + Ni), V/Cr, Fe/Ti, P/Ti, Zn/Al, and Ni/Al indicate that the PETM interval was subjected to dominantly anoxic conditions under gradually increasing primary productivity. Conditions were favorable for the formation of the glauconite bed (Bed A) at the onset of the PETM, which represent unique chemical conditions, such as a warm condition, rapid transgression, a reduced sedimentation rate, intensive continental weathering, an enhanced supply of cations, and the existence of anoxic conditions.