ORGANIC CARBON ISOTOPE PERTURBATIONS IN THE CRETACEOUSPALEOGENE ORGANIC-RICH SEQUENCE, CENTRAL EGYPT

Abstract

The Cretaceous-Paleogeneorganic-rich sediments of central Egypt are preserved as laterally extensive organic-rich successions that are represented mainly by the Duwi and Dakhla formations. Numerous studies were concerned their hydrocarbon source rock potential, trace metal accumulation, and molecular fossils composition. Very rare studies were concerning their organic carbon isotopic composition. The present study; however, investigates the 13C of bulk organic matter as well as the δC of primary productivity tracers (pristane and phytane) for samples from two drilled cores in the Quseir and Abu Tartur areas. The results of the CTOC values indicate that the organic carbon, is essentially derived from a mixture of C3 land-plants and marine plankton. The short-term variability in the δCTOC and δCTOC of the pristane and phytane across the Duwi Formation is mostly related to paleoecological factors and photosynthesis. The uppermost Duwi/lowermost Dakhla strata, which represent a maximum flooding surface, show a negative δCTOC of magnitude -1 to -2‰ and -4 to -6‰ in the bulk organic carbon and bioproductivity tracers, respectively. Such perturbation can be most probably related to density stratification and overturn, although more investigations are required for the different hypotheses.