New taxonomic and biostratigraphic data on the ?Upper Cenomanian - Turonian Radiolitidae (Bivalvia: Hippuritoidea) of Abu Roash, Western Desert, Egypt

Abstract

The Rudistae Series of Abu Roash of Egypt contains abundant radiolitid bivalves that are described herein in detail. ?Late Cenomanian - Turonian is assigned to this series. The studied sequence includes Bournonia fourtaui DOUVILLÉ, 1910, Durania gaensis (DACQUÉ, 1903), Eoradiolites cf. davidsoni (HILL, 1893), Eoradiolites liratus (CONRAD, 1852), Praeradiolites ponsianus (D'ARCHIAC, 1835), Radiolites sauvagesi (D'HOMBRES-FIRMAS, 1838), Radiolites lewyi PARNES, 1987, and Radiolites lusitanicus (BAYLE, 1857). Four species are documented for the first time in the studied area. Stratigraphically, the Rudistae Series can be subdivided into three distinct stratigraphic units. They are, from oldest to youngest: Unit 1 (?Upper Cenomanian) is represented by marl intercalated with a thin limestone bed. The rudist species Eoradiolites cf. davidsoni (HILL, 1893) and Eoradiolites liratus (CONRAD, 1852) are predominant within the upper portion of the marl bed of this unit. This bed may tentatively determine the C/T boundary in this area. Unit 2 (Turonian) consists mainly of limestone intercalated with thin beds of marls and sandy shales. These deposits frequently contain Praeradiolites ponsianus (D'ARCHIAC, 1835), Radiolites lusitanicus (BAYLE, 1857) and Durania gaensis (DACQUÉ, 1903). Unit 3 (Turonian) represents the youngest unit of the Rudistae Series. It starts with rudist- free sandy shale bed. The last limestone bed in this unit contains the thick-shelled radiolitid Durania gaensis (DACQUÉ, 1903) and numerous shells of Bournonia fourtaui DOUVILLÉ, 1910, Radiolites lewyi PARNES, 1987, and Radiolites sauvagesi (D'HOMBRES-FIRMAS, 1838).