Ichnofossils from the type area of the Grund Formation (Miocene, Lower Badenian) in Northern Lower Austria (Molasse Basin)

The trace fossils Arenicolites, Asterosoma, Diplocraterion, Zoophycos, Ophiomorpha, Saronichnus, Scolicia and Thalassinoides have been recognized in the siliciclastics of the Grund Formation. Their occurrence and distribution is related to storm deposition. In proximal storm deposits, only monospecific Asterosoma occurs. It is typical of the transition between the Skolithos and the proximal Cruziana ichnofacies. A more diverse trace fossil association of the proximal and archetypical Cruziana ichnofacies occurs in more distal storm deposits. The vertical structures (Arenicolites, Diplocraterion, Ophiomorpha) are related to opportunistic colonization of the storm beds (post-event community). The horizontal forms (Scolicia, Thalassinoides) represent fair weather conditions. The chemosymbiotic structures (Saronichnus, Zoophycos) are a record of trophic competition that pressures trace makers to deeper and more complex feeding than simple deposit feeding. The horizontal and chemosymbiotic trace fossils represent the resident community. The development from the Skolithos via the proximal Cruziana ichnofacies to the proximal–archetypical Cruziana ichnofacies indicates a deepening from the middle shoreface to upper offshore environment.