Caulostrepsis taeniola and other sclerobionts on Crassostrea gryphoides shells from the Middle Miocene transgressive deposits of the Chellala Mountains (Algeria)

The ichnological study of the Middle Miocene deposits of the Chellala Mountains (Pre-Atlas domain, Algeria) revealed relatively abundant but less diverse sclerobiont communities that are preserved in Crassostrea gryphoides shells. The most prominent trace fossil found is Caulostrepsis taeniola. Other bioerosive traces are represented by Entobia geometrica, Gastrochaenolites isp., and Trypanites isp. The four borings consist of dwelling trace fossils (domichnia) produced by polychaete annelids and endolithic bivalves. Among sclerozoans, epibionts are dominated by the two barnacle species Balanus crenatus and B. stellaris. The ichnoassemblage is assigned to the Trypanites ichnofacies, indicating nearshore, high-energy deposition influenced by storm events, and post-mortem bioerosion. The study of the mid-Miocene transgression in this key area of northern Algeria has made it possible to produce a palaeogeographic map corresponding to the period of maximum sea level.