Source rock evaluation and sequence stratigraphic model based on the palynofacies and geochemical analysis of the subsurface Devonian rocks in the Western Desert, Egypt

The Paleozoic rocks are the least explored among the subsurface successions in the Western Desert of Egypt. This contribution submits a significant record for the palynofacies and geochemical analysis for an important division of the subsurface Paleozoic rocks from Faghur-1 and NW-D302-1 boreholes. The palynofacies of the Devonian sediments of Zeitoun Formation extensively verified and classified. The palynofacies classification depended on the statistical techniques of cluster and correspondence analysis. The cluster analysis discriminated four classes of palynofacies in R-mode, which are brown wood palynofacies class R1, spore palynofacies class R2, AOM-opaque phytoclasts palynofacies class R3 and marine phytoplankton palynofacies class R4. In the Q-mode, the cluster analysis revealed three palynofacies types, which are palynofacies type C, palynofacies type B, palynofacies type A. The combination of cluster and correspondence analysis is employed to interpret the evolution of basin dynamics and the mechanisms that controlled the deposition of the Devonian rocks. Three basic environmental settings were recognized and they include 1.) Oxic highly proximal shelf setting, 2.) Oxic proximal shelf setting and 3.) Oxic distal shelf. The high oxygenation levels are confirmed by the inorganic geochemical analysis of Fe%, TS/Fe and TS/TOC in the samples from Faghur-1 borehole. The paleoenvironmental reconstruction is used to identify four 2nd order stratigraphic sequences in the studied sections, which are DevSeq1, DevSeq2, DevSeq3 and DevSeq4. These sequences are systematically described and correlated with their equivalent global Devonian Sequences. The palynofacies investigation is integrated with the inorganic and organic geochemical analysis to evaluate the potentially of hydrocarbon generation from the probable source rocks in the studied sections and its onset timing. The identified kerogen types are mostly mature (TAI range between 2 and 3 and Tmax range between 427 and 439 °C) gas prone type III with poor organic enrichment (TOC <0.9) and low potentiality for hydrocarbon production (PI range between 0.02 and 0.1). The burial history models were constructed for both boreholes; they revealed that the hydrocarbon generation started in the Cretaceous in both boreholes.