Integrated Foraminiferal Biostratigraphy and Paleoenvironmental Analysis of the Selandian- Ypresian Time Interval at Bir El-Markha Section, West-central Sinai Region, Egypt

This study examines the foraminiferal content of the late Selandian-Ypresian succession exposed at the Bir El-Markha section in the west-central Sinai region to evaluate the prevailing depositional conditions and sea-level behaviour throughout this time span. From base to top, this succession is made up of the Tarawan Formation, the Esna Formation (comprising four members: El-Hanadi, El-Dababiya Quarry, El-Mahmiya, and Abu Had), and the Thebes Formation. Seven planktonic foraminiferal biozones have been detected, including the P4 Zone (late Selandian–early Thanetian age, which is split into three further subzones P4a, P4b, and P4c); P5 Zone (latest Thanetian age); and E1–E5 zones (Ypresian age). The Selandian/Thanetian boundary is located within the P4b partial range subzone at the upper part of the Tarawan Formation, and it matches with the Maximum Flooding Surface (MFS1) of the depositional sequence 1 (DS1). The Paleocene/Eocene boundary is located at the base of the E1 partial range zone, which matches with the basal portion of the Dababiya Quarry Member (QDM) of the Esna Formation, and it is distinguished by the presence of interzonal hiatuses since the DQM's lowest portion (beds 1-3) is absent. The investigation of the depositional environments and sea-level behaviour prevailed during the examined succession's deposition is primarily based on the examination of paleoecological parameters related to its foraminiferal content, such as species diversity, P/B%, Agglutinated/Calcareous ratio (Aggl./Calc%), infaunal/epifaunal ratio, and total number of foraminiferal species, as well as their abundance patterns. Four third-order transgressive-regressive depositional sequences (DS) separated by four type-one sequence boundaries (SB) have been recognized within the studied succession, indicating a correlation with cyclic sea level changes and tectonic movements.