Ichnological data as a useful tool for deep-sea environmental characterization: a brief overview and an application to recognition of small-scale oxygenation changes during the Cenomanian–Turonian anoxic event

The oceanic anoxic event at the Cenomanian–Turonian transition (OAE-2) is a worldwide phenomenon related with variations in atmosphere–ocean dynamics. This event coincides with significant changes in the palaeoenvironment determining marine mass extinction affecting numerous groups of organisms. Ichnological analysis of the Cenomanian–Turonian boundary interval has been conducted in three selected sections from different ecological and depositional settings in the western Tethys. Indeed, a brief overview of existing knowledge in this domain highlights increasing recognition of the usefulness of trace fossils in the characterization of even minor-scale deep-sea environmental changes linked to sea-level dynamics. At the study sites, variations in ichnological features, including trace fossil composition, tiering patterns and ichnofabrics, can be related to fluctuations in bottom- and pore-water oxygenation during the Cenomanian–Turonian interval. In the Barnasiówka section (Polish Outer Carpathians), changes between oxic/ dysoxic—characterized by Chondrites, Planolites and even Thalassinoides—and euxinic conditions, without trace fossils or only with Chondrites, can be explained by variations in gravity flows influencing the benthic habitat. In the El Chorro and Hedionda sections (Betic Cordillera), longer anoxic intervals during the OAE-2, characterized by the absence of trace fossils, are interrupted by shorter dysaerobic and aerobic sub-events associated with Chondrites, Palaeophycus, Planolites, Thalassinoides, Trichichnus and Zoophycos, but showing significant differences between these two sections related to the palaeogeographically differentiated influence of upwelling conditions.