Paleoenvironmental and paleoclimatic trends during the early-middle Cenomanian in northeastern Africa (Egypt): Insights from palynomorph and palynofacies analyses

Abstract

The early to middle Cenomanian was marked by a predominant greenhouse world, with diminished ice sheets, disruptions in the global carbon cycle, and long-term eustatic sea-level rise, which led to the development of vast epicontinental and shallow shelf seas. These oceanographic and environmental instabilities influenced climate evolution and the associated vegetation communities in adjacent continental regions. During this period, the Tethys Ocean flooded much of North Africa, resulting in the deposition of thick carbonate and siliciclastic sequences. In this study, a detailed palynomorph and palynofacies investigation of twenty-eight cuttings and core samples from the Bahariya Formation in well Salam-17 of the Shushan Basin, north Western Desert (Egypt) was conducted to reconstruct the vegetation ecosystem and its response to climatic and depositional environmental changes during the early-middle Cenomanian. Statistical analysis revealed two distinct clusters of particulate organic matter (POM) components, corresponding to two palynofacies assemblages (PFA-1 and PFA-2). PFA-1, which occurred in most of the samples, is characterized by high proportions of phytoclasts, suggesting deposition in fluvio-deltaic to marginal marine environments. PFA-2 is dominated by high abundances of AOM, revealing a shallow inner shelf environment with limited terrestrial input. A rich assemblage of humidity palynomorph indicators, including fern spores, conifer pollen from Taxodiaceae and Araucariaceae, points to predominantly warm and humid climates during the early-middle Cenomanian. However, the abundant presence of aridity palynomorph indicators, such as gnetalean Elaterates and Ephedroids, along with coniferous Cheirolepidiaceae, in the upper part of the Bahariya Formation indicates a short-lived phase of semi-arid to arid conditions during the late early Cenomanian. The high abundances of megathermic plant communities suggest that a warm climate prevailed throughout the succession. Regional correlations indicate that the warm arid to semi-arid phase is coeval throughout the north Western Desert, corresponding to the early Cenomanian Elaterosporites klaszii Interval Zone.