Bioerosion traces and encrustations on orbitolinid tests from the upper Barremian (Lower Cretaceous) of Kopet-Dagh Basin, northeastern Iran

Studies on bioerosion traces and encrustations on orbitolinid tests are relatively less documented in comparison with other larger benthic foraminifera such as nummulitids and other micro-organisms. Hence, as such, these epibionts are difficult to detect in the fossil record, probably because of less working of bioerosional processes on orbitolinids. We document bioerosion traces and encrustations on the orbitolinid Paleodictyoconus from the upper Barremian rocks of the Sarcheshmeh Formation, Kopet-Dagh Basin (north-eastern Iran). Based on the study of 155 samples, four bioerosion ichnotaxa, Entobia, Trypanites, Oichnus, and Gastrochaenolites, along with encrustations by nubeculariid foraminifera, bryozoans, and a coral, are documented. These assemblages are attributed to the Entobia ichnofacies. Additionally, due to their abundance and larger test size, the orbitolinids attached to the bivalve Pinna were also a preferred substrate to settle for the larvae of smaller benthic foraminifera, as noted herein. Coincident with previous studies, the high percentage of borings and encrustation also alludes to calm waters, low rates of sedimentation, and a protected setting, thus, also favouring larval settlement on orbitolinid tests.