Distribution and Abundance of Rudist Bivalves in the Cretaceous Platform Sequences in Egypt: Time and Space

Authors : Mohamed S ZAKHERA

Pages : 745-755

Doi:10.3906/sag-1204-85

View : 15 | Download : 9

Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :As the rudist bivalves represent important organic buildups in the Cretaceous platform sequences, this study emphasizes vertical and spatial distribution of this group of bivalves in the geographic divisions of Egypt, including Western Desert, Eastern Desert and Sinai. Rudists are encountered in different rock facies ranging from mudstones to carbonates. About sixty eight species belong to twenty one genera are reported from Egypt. They belong to six families: Requieniidae, Monopleuridae, Caprotinidae, Caprinidae, Hippuritidae, and Radiolitidae. The Radiolitidae is the most diverse family, comprising eleven genera and fifty-one species, dominated by species of Radiolites, Eoradiolites and Durania. The elevator morphotype of the Radiolitidae became the dominant species in the Turonian sequences. The diversity insert ignore into journalissuearticles values(richness); peaks in the Turonian insert ignore into journalissuearticles values(36 species); Cenomanian insert ignore into journalissuearticles values(26 species); and Albian insert ignore into journalissuearticles values(9 species);, with few records in Aptian, Coniacian, Campanian and Maastrichtian insert ignore into journalissuearticles values(totally 5 species);. As yet rudists are not recorded from Santonian rocks. Geographically, rudists are highly represented in Sinai insert ignore into journalissuearticles values(60 species); concentrated in the Cenomanian insert ignore into journalissuearticles values(23 species); and Turonian insert ignore into journalissuearticles values(32 species);, followed by Western Desert insert ignore into journalissuearticles values(19 species); and Eastern Desert insert ignore into journalissuearticles values(8 species);. Regarding abundance so far, the relatively highly abundant species in Egypt are Eoradiolites liratus insert ignore into journalissuearticles values(19 sites);, followed by Praeradiolite biskraensis and Eoradiolites sinaiticus insert ignore into journalissuearticles values(7 sites for each);, Praeradiolites ponsianus, Durania humei, Radiolites sauvagesi insert ignore into journalissuearticles values(6 sites for each);, Durania gaensis and Radiolites lusitanicus insert ignore into journalissuearticles values(5 sites for each);. The rare occurrence during the Campanian and Maastrichtian may be attributed to stagnant conditions related to deposition of black shales and phosphatic deposits and the change to deep inner shelf setting respectively. The disappearance of rudists from some segments of the sequence is attributed oceanic anoxia or related to shelf drowning especially at the basal Turonian, which may related to global warming.
Keywords : Turkish J Earth Sci, 19, 2010, 745 755 Turkish J Earth Sci, vol 19, iss 6