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 δ13C of bulk organic matter as well as the δ13C of primary
productivity tracers (pristane and phytane) for samples from two drilled cores in the Quseir and Abu
Tartur areas. The results of the δ13CTOC 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 δ13CTOC and δ13CTOC 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 δ13CTOC 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.