Bulk Geochemical Characterization and Depositional Environments of Upper Cretaceous Black Shales in Wadi Qena, Eastern Desert, Egypt

Egyptian black shales occur in formations spanning various geological periods, including the Paleozoic, Mesozoic, and Cenozoic eras. These shales play a crucial role in the geochemical characterization of Egypt's sedimentary basins. This study aims to examine the depositional environment and organic matter sources of Upper Cretaceous subsurface shale strata in the Wadi Qena region of the Eastern Desert, Egypt. The distributions of paraffins, isoprenoids and sternaes biomarkers were analyzed using gas chromatography-mass spectrometry (GC-MS). Our findings indicate that the isoprenoid ratios (Pr/Ph) range from 0.276 to 0.499, suggesting an oxidizing depositional environment. Additionally, a plot of Pr/n-C17 versus Ph/n-C18 ratios provides further insights into the sources of organic matter. Samples from the Umm-Omeiyid Formation predominantly point to mixed aquatic/terrigenous organic matter, while the Abu-Tundub samples reflect land plants input. In contrast, El-Nakhil samples are positioned near the marine source boundary, indicating substantial marine organic matter input, except for sample R12. These findings shed light on the palaeoenvironmental and geochemical characteristics of the region's source rocks, emphasizing the interaction between oxic conditions and various organic matter inputs in shaping the depositional environment.