Bivalve trace fossils in an early Miocene discontinuity surface in Patagonia, Argentina: Burrowing behavior and implications for ichnotaxonomy at the firmground-hardground divide

The firmground studied here represents a co-planar surface of lowstand erosion and transgressive erosion that produced exhumation of deposits belonging to the Sarmiento Formation, providing appropriate conditions for the development of the Glossifungites ichnofacies. Differential erosion of the apertural necks, the heterogeneity of the available casting material, and the wide size range of ichnofossils suggest a complex history of colonization and erosion for this surface.