Palaeoecology And Facies Analysis Of Benthic Communities In Mid-Cretaceous Successions In The Sinai Platform, Egypt

Within the Aptian-Cenomanian formations of Sinai successions in Egypt, lateral and vertical changes occur in the numerous benthic communities. Microbenthos such as Orbitolina foraminifera and calcareous algae are widespread in the Aptian-Albian deposits in North Sinai, whereas oysters and gastropods are common in the Cenomanian siliciclastic deposits in South Sinai. In order to establish the biostratigraphy, 90 benthic and planktonic foraminifera species have been identified from the studied succession. Based on the stratigraphic distribution of the identified species the studied succession could be subdivided into three planktonic foraminiferal zones: Pseudothalmanninella ticinensis zone (Late Albian), Rotalipora cushmani zone (Middle-Late Cenomanian), and Whiteinella archaeocretacea zone (Late Cenomanian-Early Turonian). This work discusses the first record of the Albian dasycladalean alga Holosporella sugdeni (Elliott) from Sinai and reports on Montiella elitzae (Bakalova) from the Albian Risan Aneiza Formation. The occurrence of Orbitolina (Conicorbitolina) conica distinguished the Albian-Cenomanian boundary in the North Sinai sequences. The benthic communities of the studied successions indicated a faunal shift from an algal-orbitolinid foraminifera community around the Aptian-Early Albian to a rudist community during the Middle Albian and an oyster-gastropod community during the Cenomanian. This faunal shift coincided with the major sea transgression that covered North Sinai until the Middle Albian and reached South Sinai during the Cenomanian. The identified Cenomanian gastropods included Neoptyxis olisiponensis, Nerinea gemmifera, and Tylostoma bussoni. Many oyster species distinguished the Cenomanian deposits, such as Ceratostreon flabellatum, Rhynchostreon mermeti, Rhynchostreon suborbiculatum, and Costagyra olisiponensis. Identifying the benthic fauna and facies indicated a shallow inner to middle ramp environment. Stable carbon and oxygen isotope data from the Cenomanian oyster shells indicate an inner ramp environment. Comparing the carbon isotope values of the oysters with those previously recorded from the rudists may explain the different trophic levels of both groups.