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

Abstract

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.