Basal erosion and mudclast character and distribution in hybrid beds deposited in a ponded minibasin (Castagnola Fm, NW Italy)

Hybrid beds are commonplace in many deep-water clastic systems. They are characterised by a vertical association of sedimentary facies thought to be deposited under a turbulent regime (e.g. massive/laminated clean sand) and those deposited under a more transitional or cohesive flow regime (e.g. chaotic mudclast-rich and/or muddy sand), within a single event. Multiple models are proposed for their emplacement, focussing on the rheological changes within a flow, as well as their spatial and temporal occurrence. However our understanding of depositional processes, thus character and distribution of hybrid beds, remains limited. The Lower Miocene Castagnola Fm. (>1000m) records the deep-water infill of a small (a few km2 ) ponded piggyback sub-basin in the eastern part of the Tertiary Piedmont Basin (NW Italy). Six detailed sedimentary logs taken at similar distances along a 3.1 km proximal-to-distal transect encompass a low net-to-gross (0.2), 250 m thick interval. Generally, bed types comprise either thin (