Styles of failure in late Holocene highstand prodelta wedges on the Adriatic shelf

On the continental shelves of the northern Mediterranean basin, the late Holocene highstand systems tract (HST) prograded under the influence of major rivers, after the attainment of the present sea-level highstand (about 5.5 cal kyr BP), On the Adriatic shelf, the thickness distribution of the late Holocene HST reflects the location of major deltas on the western side of the basin and the geostrophic circulation, which prevents a more uniform sediment dispersal toward the center of the basin. Very high sediment accumulation rates (1 to 10 cm/year) resulted in the construction of a HST depocenter up to 35 m thick. This shore-parallel depocenter is affected by failure of limited displacement over as much as 40% of its extent, Gas impregnation is common in the topset region and occurs at very shallow levels (a few meters) below the sea floor, Five areas are characterized by a variety of sea-floor and subsurface crenulations. Although locally some of these crenulations have an intriguingly regular geometry, sediment failure is the most plausible mechanism for their formation. Sediment failure better explains the large variety of geometries that characterizes the coastal mud prism of the late Holocene HST. Furthermore, we observe that these crenulations occur only where the downlap surface at the base of the HST is disrupted and affected by geometries that are consistent with fluid escape processes, This relationship suggests that the basal surface acts as a weak layer for sediment failure.