Integrated palaeo-environmental proxies of the Campanian to Danian organic-rich Quseir section, Egypt

Abstract The Cretaceous-Palaeogene sequence of Egypt is a part of a giant belt of organic-rich deposits in North Africa and the Middle East. The present work focuses on changes in trace element, bulk organic, and lipid biomarker inventories archived in sediments of the Duwi and Dakhla formations of the Quseir section in the Red Sea area. The studied section can be divided into 6 geochemically constrained units: the lower, middle, upper and uppermost members of the Duwi Formation (Fm) and the Hamama and Beida members of the Dakhla Fm. The composition of kerogen is found to vary significantly among these units. The lower and upper members of Duwi Fm are typified as land-derived type-III kerogen. The middle and uppermost members contain type-II kerogen. Most of the Dakhla Fm is typified by type-II kerogen with the exception at the lowermost and middle Hamama member and middle part of the Beida member that contain type-I kerogen. The repeated occurrence of photic zone anoxia as indicated by the presence of aryl isoprenoids was accompanied by strongly reducing conditions in the bottom waters and in sediments. This led to strong enrichments of some redox sensitive elements like molybdenum. Photic zone anoxia preferentially occurred during marine transgressions, in accord with high hydrogen indices typifying marine organic matter. However, such periods were interrupted by periods of increased input of terrigenous material, reflected by high aluminium contents and type-III kerogen. Overall, low temperature of maximum generation (T max ), odd-over-even predominance of n -alkanes, the preservation of carboxylic acids, and a predominance of biological 17β,21β(H) hopanoids over their geological 17α,21β(H) stereoisomers reveal that the organic material of the Quseir section is immature to at best moderately mature. The observed dominance of rearranged steranes (diasterenes) is consequently best explained by enhanced clay catalysis, rather than by thermochemical alteration. Additionally, the biomarker inventory of the Quseir section corroborates that eukaryotic algae were affected by the extinction event at the Cretaceous-Palaeogene boundary to a much greater extent than bacteria including bacterial primary producers.