A microscale analysis of Bolonia from the Cretaceous of Patagonia sheds light on an enigmatic tracemaker

COMERIO, MARCOS; PAZOS PABLO J.; GIACHETTI; GUTIERREZ CAROLINA; FERNANDEZ D.E,; HEREDIA, ARTURO M.

Alabama

Workshop; VI International Ichnofabric workshop; 2021

University of West Alabama

Bolonia Meunier has been recorded from positive epireliefs in marine deposits from the Ordovician to Eocene of both hemispheres. This ichnotaxon is characterized by two lobes with biserial pads and a heart-shaped cross-section. For many years, this name did not prevail and trace fossils that should have been assigned to Bolonia were assigned to other ichnogenera (e.g., Scolicia, Protovirgularia). The last revision of this ichnogenus was made by Schlirf (2002), who retained the ichnotaxon as valid and emended the diagnosis allowing a clear differentiation from the previously mentioned ichnogenera. Gastropods, polychaetes and irregular echinoids have been suggested as tracemakers. Recently, Bolonia was found in Lower Cretaceous deposits of the Agrio Formation in the Neuquén Basin, Argentina. The specimens were documented in sandstones interbedded with siltstones/claystones and associated with wave and current ripples (including interference ripples) indicating shallow-marine deposition above wave base. Samples of Bolonia were analyzed microscopically through serial thin sections transverse and parallel to the bedding plane (Fig. 1.A). For the first time, the internal structure of Bolonia from one selected sample with high lithological contrast and exceptional preservation is described herein.