Bioerosion in fossil cephalopods: a case study from the Upper Carboniferous Buckhorn Asphalt Quarry Lagerstätte, Oklahoma, USA

The mid-Pennsylvanian (Desmoinesian–Virgilian) deposits from the Buckhorn Asphalt Quarry Lagerstätte near Sulphur, Oklahoma, are characterized by siliciclastic–carbonate rocks. One of these deposits is the ‘cephalopod coquina’ that contains a large amount of orthocerid and coiled nautiloid, and ammonoid shell remains. These were used for a detailed study on bioerosion in cephalopod shells in order to help in the reconstruction of the paleoenvironment and to increase the general knowledge on bioerosion in fossil cephalopods. More than 50 shell fragments were cast and investigated. The shells cast and investigated in this study comprise a diverse set of ichnotaxa-/forms. Besides chlorophyte and cyanobacterial traces, also rhodophyte, fungal, and spongal traces are present as well as those of unknown origin. In addition, there are six ichnoforms that might have foraminiferans as producers. In orthoceratids, Ichnoreticulina elegans and a curly morphotype of Scolecia isp. are most common while the abundance in coiled cephalopods is dominated by the ‘superthin form’, the ‘extremely thin form’, and Flagrichnus profundus. In total, 22 ichnotaxa and -forms were recognized and 12 of these have their oldest record in the Carboniferous. The succession of ichnotaxa/-forms in the casts of orthocones suggests deposition in the deep euphotic to dysphotic zone of the Buckhorn sea while shells of coiled specimens had drifted for a while; they were therefore more prone to bioerosion by autotrophs until they sank to the seaflo