Ichnological analysis of the Messinian-Zanclean (Miocene-Pliocene) transition at Eraclea Minoa (Sicily): Tracemaker response to the Terminal Messinian Flood

A detailed ichnological analysis has been conducted, for the first time, of the Arenazzolo and Trubi formations of the Caltanissetta Basin in Sicily. Aim of this analysis is to evaluate paleoenvironmental changes affecting macrobenthic tracemaker communities during the re-flooding of the Mediterranean at the end of the Messinian Salinity Crisis. The uppermost Messinian Arenazzolo Formation is characterized by a scarcity of trace fossils, probably related to high energy depositional conditions, and perhaps no fully normal salinity level yet, resulting in an unfavourable habitat for macrobenthic tracemaker communities. The exclusive presence of small traces (Chondrites) sparsely distributed in several horizons is associated to intermittent phases of lower energy conditions facilitating colonization by opportunistic tracemakers. A significant change in trace fossil assemblages is observed at the transition to the Zanclean Trubi Formation. Here the ichnofossil assemblage consists of?Arenicolites, Chondrites, Halimedides, Palaeophycus, Planolites, Thalassinoides, Trichichnus and Zoophycos, assigned to the Zoophycos ichnofacies, revealing an abundant, diverse, well-developed, multi-tiered, tracemaker community. This change observed at the Messsinian/Zanclean boundary is related to the rapid establishment of normal, full-marine, conditions with well oxygenated bottom- and pore-waters, and food availability in a deep marine environment. Comparison with previous micropaleontological studies supports the magnitude of the paleoenvironmental change affecting both pelagic and benthic environments.