Cenomanian-Turonian rudists from Western Sinai, Egypt: Systematic paleontology and paleoecology

摘要

The Cenomanian-Turonian sequence is well exposed in western central Sinai and contains a considerable number of rudist species. The identified rudists belong to Radiolitidae, Hippuritidae and Requieniidae. Fifteen species are described, belonging to ten genera: Requienia, Toucasia, Apricardia, Radiolites, Eoradiolites, Praeradiolites, Sphaerulites, Sauvagesia, Hippurites, and Vaccinites. Eleven species are reported in the Cenomanian and four species in the Turonian. Within the Cenomanian, two new species are described: Requienia tortuosi and Eoradiolites lenisexternus. The genus Requienia and the species Apricardia carentonenis d'Orbigny, Eoradiolites syriacus (Conrad), Sphaerulites agariciformis Delamétherie, Sphaerulites depressus Blanckenhorn and Vaccinites cf. grossouvrei (Douvillé) are reported for the first time from Egypt. The Cenomanian and Turonian rudists in the western Sinai show either elevator or clinger morphotypes, with the predominance of the former type; recumbent mode of life is rarely represented by some Requieniidae. The elevators are of isolated and clustered occurrences and more represented in the Cenomanian sequence. Rudists of the study area are mainly of parautochthonous fabrics with low to dense packing. Autochthonous fabrics are also achieved by some species, mainly in the Turonian. The disappearance of rudists from the middle part of the sequence and above the Cenomanian/Turonian boundary is due to a deeper setting that resulted from sea-level rise or seafloor subsidence (shelf drowning). The occurrence of rudists with oysters and other benthic fossils in the siliciclastic and carbonate sediments of the Cenomanian and Turonian sedimentary rocks in the Sinai indicate that the sequence was deposited on a broad, shallow shelf. Although the first marine transgression invaded the central Sinai in the late Cenomanian, transgressive deepening conditions continued until the Turonian. The rudists of central Sinai are of Tethyan affinity with significant relation with North Africa, the Middle East, and Southern Europe.