Bartonian coral biostromes in a storm-dominated ramp setting of the El-Ramliya-Akheider block: sedimentology, sequence stratigraphy and regional paleogeographic insights, Cairo-Sukhna region, Egypt

Abstract

Scleractinian coral reefs are pivotal carbonate producers in the late Cenozoic era, they are useful in understanding the early Paleogene thermal events. Despite challenges in studying the Eocene due to scarce data and poor outcrop quality, the El-Ramliya-Akheider block has provided critical insights into its Bartonian carbonate succession. The succession is characterized by extensive coral carpets (biostromes) and a wide range of sedimentary structures, including large-scale channels. To investigate the facies organization and sedimentary pattern of the succession, we integrated sedimentological (outcrop studies, facies analysis) and paleontological approaches. Acropora coral carpets, which thrived in mid-ramp settings, have been altered by sedimentological changes caused by storm currents. The inner ramp environment with bioshoals of larger miliolids and seagrass meadows shows a rhythmic intercalation pattern with biostromes. This intercalation, along with the formation of channels filled with carbonate fragments, is influenced by the dynamic interplay of storm-driven currents and return currents. The presence of coral fragments (coralline float-/rudstone) as para-to allochthonous accumulations suggests that coral colonies initially grew as carpets in a calm, mid-ramp environment. These fragments were subsequently transported and redeposited during storm currents. The return currents generated channel deposits (abraded foraminiferal pack-/grainstone) characterized by large-scale cross-beddings. These channels, filled with inner-ramp foraminiferal pack-/grainstone, were scoured into the mid-ramp coral biostromes, highlighting the significant role of storm-related processes in sediment transport and channel formation. Notably, coral biostromes in a stable, euphotic mid-ramp setting mark the earliest recovery during the Bartonian cooling period after the Middle Eocene Climatic Optimum event (MECO). The dominance of Bartonian lagoonal marine conditions in the Cairo-Sukhna region is attributed to global transgression, shallow depositional basin, and restricted water circulation caused by uplifted barriers. Overall, this study enhances understanding of the Eocene paleoenvironment and the capability of coral ecosystems.