Sedimentary facies and stratal architecture of the Middle Eocene Acropora-dominated succession in a storm-influenced ramp system, El-Ramliya area, north Eastern Desert, Egypt

• Published in: Sedimentary geology Vol. 447; p. 106368
• Main Author: El-Azabi, Mounir H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2023
• Subjects: Acropora; Carbonate cycles; Egypt; Middle Eocene; Palaeoenvironment; Storm-influenced carbonate ramp; Storm-influenced carbonate ramp; Acropora; Carbonate cycles; Palaeoenvironment; Egypt; Middle Eocene
• ISSN: 0037-0738; 1879-0968
• DOI: 10.1016/j.sedgeo.2023.106368

A shallow tropical carbonate succession of cyclic deposits rich in coral fragments and benthic foraminifera typifies the Middle Eocene in the El-Ramliya area, north Eastern Desert of Egypt. This succession displays distinctive features such as the prominent appearance of the genus Acropora, meter-scale shallowing facies trends, and carbonate-filled channels. In order to establish a better understanding of the internal facies architecture and depositional patterns of the El-Ramliya succession, an integrated sedimentological and paleontological approach is used. The genus Acropora, along with Astrocoenia, Goniopora and Dictyaraea, represents the coral fragments. This typifies the oldest record of the genus Acropora to date in Egypt. The record reinforces that Acropora appeared as a locally dominant coral assemblage in the Middle Eocene of southern Tethyan province, earlier than previously thought in the Late Oligocene worldwide. Allo- to parautochthonous accumulations of coral fragments (Acropora rudstone and floatstone) deposited during severe storms indicate an earlier growth of shallow-water carpets of Acropora and other corals in a low energy, mid-ramp setting. That facies alternates with deposits dominated by porcelaneous foraminifera formed in an inner ramp (foraminiferal wacke-/packstone and wackestone). Facies dominated by Acropora and porcelaneous foraminifera exhibit repeated shallowing-upward cycles related to periodic, small-scale transgressive–regressive events. Acropora shows a slight deepening of the environment followed by an upward shallowing trend dominated by larger porcelaneous foraminifera, sometimes linked with carbonate-filled channels. These cycles are consistent with a low-amplitude eustasy that generated repeated high-frequency changes in accommodation space required for cyclic deposition. Bottom return currents related to storm surges created the channel deposits. Thus, the driving force for sediment transport was storm-influenced currents that led to coral accumulations and channel fills. Sediment accumulation on the carbonate ramp developed at a time of relative tectonic quiescence during a period of rising eustatic sea level linked with a warm climate. Ecological variables such as water depth, light availability, nutrient levels and atmospheric carbon dioxide concentration have profound impacts in controlling the growth of coral communities. •El-Ramliya is one of the few middle Eocene records of Acropora worldwide.•It offers valuable information for the characterization of Paleogene reefs.•Storm-induced currents generated coral accumulations and carbonate-filled channels.•Low-amplitude eustatic changes related to orbital forcing cause high-frequency cycles.•Ecological parameters play key roles in controlling the growth of coral reefs.