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During the Late Cretaceous (Cenomanian), significant disruptions in the carbon cycle, global warming, and episodes of oceanic anoxia occurred, leading to the deposition of organic carbon-rich sediments. In well BED2-3, located in the BED2 gas field within the Abu Gharadig Basin (north Western Desert, Egypt), the lower-to-middle Cenomanian Bahariya Formation displays thick alternating layers of sandstones, siltstones, and shales. Detailed geochemical analyses were conducted on thirty-three cutting samples from the Bahariya Formation, focusing on total organic carbon (TOC), whole-rock elemental geochemistry, and carbonate content. These geochemical measurements provided valuable information regarding paleoredox conditions, marine biological productivity, terrigenous sediment influx, weathering and paleoclimate conditions, and mechanisms influencing organic matter accumulation. The enrichment factors (EF) of redox-sensitive trace elements were utilized to infer oxygenation conditions and marine biological productivity during the deposition of the Bahariya Formation. The stratigraphic distribution of redox-sensitive elements allowed for the Bahariya Formation to be categorized into lower and middle-upper intervals. The results revealed that the lower interval exhibited strong-to-enriched EF values of redox-sensitive elements and fair-to-rich TOC content, indicating a prevalent anoxic setting during deposition. In contrast, the middle-upper interval displayed weakly-to-slightly enriched EF values with poor-to-fair TOC content, suggesting deposition under oxic-suboxic redox conditions. By examining Al-normalized redox-sensitive ratios and their correlations with TOC content, significant relationships were observed in the lower interval, indicating a coupling between the enrichment of redox-sensitive elements and organic matter. This suggests enhanced biological productivity during deposition of the lower interval compared to the relatively low productivity during deposition of the middle-upper interval of the formation. These conditions controlled the production and preservation of organic matter in the lower interval, while the middle-upper interval suffered from organic matter dilution and destruction due to an increased influx of terrigenous material and lower biological productivity. Geochemical proxies related to detrital materials provided evidence of alternating terrigenous sediment flux, consistent with shifts between coarse- and fine-grained fractions and related facies of sandstones, siltstones, and shales. These findings align with active continental weathering in the source terrane and deposition under enhanced warm-humid climatic conditions, with intermittent arid-to-semi-arid phases. These conclusions are further supported by the palynomorph assemblages and clay mineralogy within the Bahariya Formation. [ABSTRACT FROM AUTHOR]

The Middle Jurassic was a time of marginal to shallow shelf settings dominated by organic matter-rich deposition in northern Egypt, southern Tethys. Paleoenvironmental and sequence stratigraphic reconstructions are of paramount significance for a better understanding of basin history and related reservoirs and source rock units. For this purpose, a detailed palynomorph and palynofacies analysis of the Middle Jurassic Khatatba Formation in the Dahab-Mireir Basin, north Western Desert, was conducted. A moderately to well-preserved, moderately diverse palynomorph assemblage of spores, pollen, and dinoflagellate cysts is identified. Marker dinoflagellate cysts, including Dichadogonyaulax sellwoodii, Escharisphaeridia pocokii, Gonyaulacysta adecta, Korystocysta gochtii, Pareodinia ceratophora, and Wanaea acollaris, defined a Bajocian to Callovian age. Palynofacies analysis of the Khatatba Formation revealed two assemblages, whereby PFA-1 is the most abundant in the study well and is comprised mainly of terrestrial phytoclasts deposited nearby fluvio-deltaic sources. The infrequently reported PFA-2 consists of moderate abundances of phytoclasts and AOM, deposited in an inner shelf environment. A more reliable paleoenvironmental interpretation was indicated based on three palynomorph assemblages. The spore-dominated assemblage indicated deposition in a deltaic environment, while the mixed palynomorph assemblage revealed fluvio-deltaic to marginal shallow marine conditions. The microplankton-dominated assemblage is represented by minor samples and reflects an offshore inner shelf condition. Furthermore, the Middle Jurassic relative sea level was reconstructed based on the quantitative variations in the terrestrial/marine (T:M) ratios and abundances of spores, pollen, and dinoflagellate cysts. This led to the subdivide of the Khatatba Formation into thirteen third-order transgressive-regressive sequences, which can be correlated with the global Jurassic short-term sea level changes. Active tectonics and accelerated drifting of the Eurasian Plate during the Middle Jurassic are suggested to control basin uplift/subsidence and, therefore, recurring patterns of relative sea level change. [ABSTRACT FROM AUTHOR]