Sequence stratigraphy of Holocene deposits in the offshore of Venice based on very high-resolution seismic profiles

Very high-resolution seismic profiles allow a sequence-stratigraphic analysis of the Holocene deposits off the Venice Lagoon. The succession is bounded at the base by an unconformity (sequence boundary), well recognizable in seismic profiles, which crops out at seaward locations. In the lower part of the Holocene succession, zones showing sub-horizontal and hummocky reflectors are separated by channelized deposits, interpreted as estuarine channel fills and distributary channel-levee systems. A sharp surface, climbing landward, truncates the lower Holocene deposits. This is overlain by a prograding shallow-marine wedge, which represents the upper part of the succession. This wedge consists of a regressive shoreface-shelf system and, locally, of ebb-tidal deltas off the lagoon inlets. The lower part of the Holocene succession is interpreted as a transgressive systems tract, deposited during the high-amplitude sea-level rise that followed the Last Glacial Maximum. A wave ravinement surface marks the marine ingression of the late transgressive phase, and is approximately coincident with the downlap surface in seismic profiles. The prograding shallow-marine wedge represents the highstand systems tract. During this latter phase, the rate of sediment supply outpaced that of creation of accommodation. The variable thickness distribution of the TST documents important changes in the stratal architecture of the Holocene deposits along both depositional strike and dip, which may be in part due to antecedent basin physiography.