Optimized event stratigraphy of Cenomanian-Turonian ostracods of North Africa and the Middle East

Abstract

During the Cenomanian and Turonian, high eustatic sea levels combined with subsidence of North Africa resulted in widespread marine inundation and the evolution of an indigenous benthic fauna, including many endemic ostracod taxa. This is the first study to combine all information on the ranges of Cenomanian and Turonian ostracods and associated planktonic foraminifera across North Africa and the Middle East into a single event-stratigraphic composite scale. Information includes the ranges of the taxa in measured sections and wells in published articles and in unpublished theses and dissertations. Nine events are tracked across the region and are used to subdivide sections and wells into subsections whose boundaries separate older sections below from younger sections above. Pseudosections were coded to represent the older and younger surfaces of the events that are separated by a very thin interval. The subsections provide a geologic framework of ordered packages of sections and associated biologic events. In this methodology, the sequence stratigraphy is an integral part of the biostratigraphic analysis. This study includes 121 sections and wells that were subdivided into 218 sections and subsections, including the nine pseudosections, the first and last occurrences of 189 taxa, and 18 unpaired events, which resulted in a total of 396 events. This information was coded into software that uses a heuristic algorithm to optimize the sequence of events. The resulting composite was used to correlate the sections and subsections, produce range charts, and calculate diversity of ostracods. Computer runs were made for each of the four study areas (Morocco and western Algeria, eastern Algeria and Tunisia, Egypt, and the Southern Levant) separately and unitedly. Run separately, diversity peaks reflect biases of the local available information, but the combined results show steady rates of evolution and extinction that produced a peak in diversity of 66 species in the late Cenomanian. There are no mass extinction events. The continued faunal turnover also indicates that there is no community stasis in the Cenomanian-Turonian ostracods of the region.