Paleoecology and paleobiogeography of the Cenomanian-Turonian bivalves from the Southern Galala Plateau (Eastern Desert, Egypt)

Fifty-three bivalve species from the Cenomanian-Turonian strata in the Southern Galala Plateau (Eastern Desert, Egypt) were used to identify major factors controlling their regional and global distribution. Non-metric multidimensional scaling (NMDS) indicated that rock type is a major factor controlling the bivalve distribution, while other biotic parameters such as life habit and mobility level have a minor role. Although the diversity and density of bivalves have a punctuated pattern, a general trend of increasing diversity from the Cenomanian onward was observed. In contrast to the Cenomanian, mobile and infaunal species have dominated the Turonian in a low-energy deeper marine environment with an oligotrophic regime. The lower diversity, the rarity of infaunal taxa, in addition to abundant authigenic minerals (glauconite/pyrite) and oyster bivalves in the Cenomanian point to a high-stress environment, where dysoxia at (or just below) the sediment/water interface may exclude the infaunal taxa. Analysis of the geographic distribution of the identified taxa indicates no significant difference between the Middle East and other mega-provinces. The planktotrophic larval development mode of most bivalve taxa (e.g., oysters and heterodonts) and the opening of seaways associated with the global Cenomnian/Turonian flooding may have resulted on wider geographic dispersion and mixing of faunal communities among the different provinces.