Response of Bathonian–Oxfordian transgressive-regressive cycles on foraminiferal morphogroups, and diversity: a case study from shallow marine deposits in north Gulf of Suez, Egypt

The analysed samples originate from the commercial well GS 91 drilled in the northern Gulf of Suez, Egypt. It covers a 488-metre-thick Bathonian-Oxfordian section representing the Upper Safa and the Lower Masajid formations. Detailed taxonomic analyses resulted in the identification of 61 foraminiferal species belonging to 34 genera, which are applied to the delineation of Five benthic biozones. Based on test morphologies, nine infaunal and eight epifaunal morphotypes are distinguished to apply in palaeoenvironmental assessments. Lithological and faunal changes observed in the well section allowed the identification of three sea-level cycles. Each cycle includes a transgressive phase dominated by limestone and marl, representing inner shelf carbonate platform facies, and shale to sandstone facies formed during periods of increased palaeowater depth. The first cycle encompasses the upper part of the Safa Formation. Its transgressive phase contains nearly equal amounts of infaunal and epifaunal components indicating oxic conditions, while most of its highstand phase contains almost only epifaunal morphotypes, suggesting an oxygen-depleted condition. In the lower part of the Masajid Formation, two sea-level cycles are distinguished, both containing entirely or dominantly infaunal components indicating normal marine oxygenation.