Depositional environments and source rock potential from molecular to basin scales: An example from the Middle to Upper Cretaceous succession, Abu Gharadig Basin, Egypt

Abstract

We present a case study of high-resolution screening and integration of palynological and organic geochemical methodologies in the TSW-21 well in the Abu Gharadig Basin, north Western Desert of Egypt. A total of 84 cores and cuttings samples were analyzed for TOC wt%, Rock–Eval pyrolysis, molecular geochemistry, vitrinite reflectance (R_o%), and palynology. The categorization of dispersed organic matter in palynological macerals shows that it differs not only in palynofacies properties but also in distinct palynomorph characteristics (mainly abundance, diversity, marine versus non-marine, and preservation). The work highlights the value of integrating optical and geochemical methods in screening hydrocarbon source rock potential, and the implications for kerogen examination and the reconstruction of depositional environments. In the present study, data indicate a marine, near-shore depositional environment of the middle Cretaceous Bahariya Formation, and more open-marine conditions for the overlying strata of the Upper Cretaceous Abu Roash Formation. A variety of kerogen types (II/III, II, III, and IV) is predominant in the Bahariya Formation and is mainly gas-prone (highly phytoclastic and rich in amorphous organic matter [AOM]). In contrast, the Abu Raoash Formation yielded highly oil-prone Type II > I kerogen (AOM-rich). Thermal maturity proxies including Rock–Eval pyrolysis (T_max), R_o%, and Spore Coloration Index (SCI) reveal that the Bahariya and Abu Raoash formations are immature.

Graphical Abstract