Lateral facies changes and architecture of hybrid-like beds deposited in a ponded minibasin (Castagnola Fm, NW Italy)

Hybrid-like beds (HEBs) are a class of gravity flow deposit including a basal sandy division followed by a chaotic division made up of both sand and clay in different proportions sometimes capped by an upper structured clean sandstone division. Although their existence has been documented nearly from the onset of the turbidite concept, HEBs have been the object of renewed attention in the last ten years, mainly as they can occur within hydrocarbon reservoirs. A range of generation mechanisms has been suggested, partly reflecting the wide variety of such deposits. Most models focus on the occurrence of rheological changes within the flow, with the chaotic mud-enriched division being deposited under transitional or laminar conditions. HEBs are thought to be more common at fan fringes or in close proximity to confining topography. However their depositional processes remain an object of on-going research, and thus our understanding of their character and distribution continues to evolve. The Lower Miocene Castagnola Turbidite System (800-1000m thick) records the deep-water infill of a small (a few to tens of km2) ponded piggyback sub-basin in the eastern part of the Tertiary Piedmont Basin (NW Italy). Six detailed sedimentary logs taken along a 3.1 km proximal-to-distal transect encompass a low net-to-gross (0.2), 250m thick interval. Generally, bed types comprise either thin (