Climatic variability and silicate weathering are remarkable features throughout the Late Cretaceous period. Late Campanian black shale is considered the most significant silicate source rock in the southern Tethys. Here, we used mineralogical and geochemical data to evaluate the continental weathering intensity and climatic changes as well as their impact on the deposition of the Late Campanian black shale in the Western Desert of Egypt. The studied black shale has a relatively high concentration of Al, Fe, Mg, Ca, Sr, Ga, Co, Cr, and V when compared to the average Post-Archean Australian Shales (PAAS). The studied samples have elevated values of Ga/Rb, and low values of Rb/Sr, Sr/Cu, and K₂O/Al₂O₃, supporting the deposition of Late Campanian shale under warm/humid conditions. Furthermore, the average chemical index of alteration (CIA, 78.6%), chemical index of weathering (CIW; 83.8%), C-value (1.26), Fe/Mn (408), and Mg/Ca (1.54) reveal the predominance of warm/humid climate. The chemical weathering proxies (CIA, CIW, PIA, LnAl₂O₃/Na₂O) and ACNK diagram imply that the Late Campanian samples were exposed to a moderate grade of chemical alteration. The deposition of black shale occurred under high seawater salinity conditions based on Sr/Ba (Avg = 3.6). Additionally, the weathering indices are well correlated with paleoclimatic proxies, suggesting that weathering intensity is strongly affected by paleoclimate. However, chemical weathering during the Late Campanian has a weak influence on oceanic nutrient fluxes. No substantial impact of the paleoclimate during the deposition of Late Campanian black shale on water salinity was reported.

Maastrichtian organic-rich sediments of Egypt were deposited under a warm greenhouse climate along the stable African shelf. This study presents an integrated analysis of the geochemical, mineralogical, and palynological data from Maastrichtian organic-rich sediments in the northwest Red Sea region of Egypt. The aim of the study is to assess the impact of anoxia on the enrichment of organic matter and trace metals and to reconstruct a model for the formation of these sediments. The sediments are hosted within the Duwi and Dakhla formations, covering an interval of ∼1.14-2.39 million years. Our data indicate variable bottom-water oxygen-level conditions for early and late Maastrichtian sediments. The C-S-Fe systematics and redox geochemical proxies (e.g., V/(V + Ni), Ni/Co, and U_authigenic) suggest dysoxic to anoxic depositional conditions for the late and early Maastrichtian organic-rich sediments, respectively. The early Maastrichtian sediments contain abundant small-sized framboids (average = 4.2-5.5 μm), suggesting anoxic conditions, while the late Maastrichtian sediments have larger framboids (average = 4-7.1 μm), indicating dysoxic conditions. The palynofacies analyses reveal the high abundance of amorphous organic matter and confirm the predominance of anoxic conditions during deposition of these organic-rich sediments. The early Maastrichtian organic-rich sediments have a significant Climate concentration of Mo, V, and U, indicating high biogenic production rates and distinct preservation conditions. Additionally, the data imply that oxygen deficiency conditions and low sedimentation rates were the main factors controlling the preservation of organic matter in the studied sediments. Overall, our study provides insights into the environmental conditions and processes that led to the formation of the Maastrichtian organic-rich sediments in Egypt.