Late-glacial marker beds of various origins - megaturbidite, sapropel, tephra - exhibit lateral variability enhanced by tectonics in the Western Ionian Basin (central Mediterranean)

Marker beds are tools for stratigraphic correlation and may constitute the backbone of basin analysis and chronostratigraphy. They are defined as thin beds with a distinctive character, widely distributed and traceable over large areas, across diverse depositional environments. They may vary systematically in thickness within basins, for example, tephra layers decrease in thickness away from the eruptive source. There are, however, basins with complex morphologies where the intrinsic variability is enhanced by regional or local factors such as tectonics. We explore such variability from a detailed late glacial to recent record in a proximal to distal transect of five sediment cores in the Western Ionian basin. Two significant results arise from this study. First, the well-known Augias marker bed, found extensively in the Ionian abyssal plain since the 1980s, is found in a series of discontinuous depocenters within wedge top basins of the Calabrian accretionary wedge. Furthermore, it is coeval with a turbidite present in shallower settings, even if it is unclear whether these deposits represent the downstream evolution of a single gravity flow or a series of coeval events. Second, sapropel S1 is a cm-thick marker correlatable across the eastern and central Mediterranean. In the study area, sapropel S1 is synchronous with a succession of up to 15 m of finely laminated turbidite-hemipelagite couplets devoid of bioturbation. This exceptionally preserved deposit allows us to trace sediment transport and accumulation related to gravitational instability and possibly times of increased precipitation with unprecedented detail during the early Holocene.