Depositional and erosional coastal processes during the last postglacial sea-level rise: An example from the central Tyrrhenian continental shelf (Italy)

A transgressive systems tract (TST) deposit on the inner continental shelf of the south Tuscany region (central Tyrrhenian Sea, Italy) formed during the last postglacial sea-level rise. Its small-scale stratigraphy has been detailed using high-resolution seismic profiles, gravity cores, and grab samples. The TST deposit overlies a lowstand unconformity, shows a tabular geometry, and comprises three internal architectures of beach facies: (1) Architecture A, present on the outer sector of the study area, is made up of only a reworked sand sheet; (2) Architecture B, on the middle sector, comprises palustrine (bottom), washover, and the above-mentioned reworked sand sheet; and (3) Architecture C, on the inner sector, represents the absence or scarcity of deposits (reworked sand sheet) over the unconformity. Because the lateral distribution of these vertical successions is not random, but parallel to the coast, each architecture represents an individual sedimentary stage during sea-level rise. However, all architectures were formed via shoreface retreat in response to the landward migration of a beach complex over the unconformity. During this migration the beach system was characterized by a source diastem located in the surf zone and by two sediment dispersal systems, One moved the eroded sand over the flat back-barrier palustrine area by storm washover, while the other transported part of this sand to the lower shoreface, forming a reworked sand sheet above the older and inactive source diastem (ravinement surface). The TST architectures originated from a transgressive succession of beach facies, differentiated according to the intensity of shoreface retreat. Architecture A represents a low preservation potential of the original beach complex, Architecture B relatively high preservation, and Architecture C no preservation. The intensity of erosion and the consequent preservation potential were totally controlled by antecedent topography.