Upper Cretaceous (Coniacian-Santonian) low diversity oyster-dominated macrofaunal association in the Eastern Desert of Egypt: Taphonomy versus ecology

Abstract

In contrast to the Cenomanian-Turonian, the Coniacian-Santonian macroinvertebrates of the Middle East and North Africa are rarely investigated. Previous investigations indicated the occurrence of low diversity faunal associations, which can be attributed either to ecological (primary/biogenic) or taphonomic (secondary/sedimentologic) factors. The poorly preserved macrofauna of the Hawashia Formation (north Eastern Desert, Egypt) has been quantitively analyzed resulting in the identification of fifteen macrofaunal species including five bivalve, seven gastropod, two ammonite taxa, and one echinoid taxon. The occurrence of the ammonites Metatissotia fourneli Bayle and Texanites (T.) texanus Roemer confirm the Coniacian‒Santonian age for the Hawashia Formation. Based on litho- and biofacies, this fauna likely lived in a normal oxygen tidal-influenced shallow subtidal environment under arid conditions. Taphofacies indicates a low-energy regime with low sedimentation rate. Most shells are highly damaged (encrusted, bioeroded, and fragmented) due to their long residence time in the Taphonomic Active Zone (TAZ). Few of the benthic species have a wide geographic distribution (e.g., Oscillopha dichotoma), which generally imply low sea-level. In contrast, ammonites have been precariously recorded from Africa, Europe, and Asia in addition to South America, outlines a cosmopolitan attitude.