Coastal dynamics under conditions of rapid sea-level rise: Late Pleistocene to Early Holocene evolution of barrier–lagoon systems on the northern Adriatic shelf (Italy)

Abstract

This multidisciplinary case study of two preserved barrier systems combined the analysis of radiocarbon datings, grain-size distributions, high-resolution seismics, and shelf bathymetry with reconstructions of palaeo-environmental conditions (tides, waves, sea-level change) and forward modelling of barrier-lagoon systems, to provide an integrated view of the coastal transgressive evolution of a large sector of the northern Adriatic shelf between 15 and 8 ka BP. Palaeoenvironmental reconstructions point to increased tidal amplitude, low-energy wave climate and high rates of sea-level rise (up to 60 mm/a) during the formation of the oldest preserved barrier system (not, vert, similar90 m water depth; 14.3 cal ka BP). A younger barrier system (42 m water depth; 10.5 cal ka BP) formed under conditions of lower tidal amplitude, higher wave energy and a lower rate of sealevel rise (10 mm/a). Forward modelling suggests that the probability of barrier-island overstepping during transgression is inversely proportional to tidal amplitude, if all other factors are assumed equal. The oldest barrierlagoon system developed under conditions of large tidal amplitude, which permitted rapid transgression. However, this system apparently failed to keep up with the anomalously high rate of sea-level rise resulting from melt-water pulse 1A. The youngest barrier system appears to have drowned in place due to antecedent topography. As the barrier system transgressed over an ancient Pleistocene alluvial plain, the rapid increase in backbarrier accommodation caused an abrupt disequilibrium between shoreface and backbarrier sedimentation, which led to barrier overstepping. Although BarSim modelling indicates that tidal deposition can reduce the probability of barrier overstepping, there are other driving mechanisms (in our case extremely rapid sea-level rise and antecedent topography), which are more determinative in explaining the transgressive coastal evolution of barrier-lagoon systems in the northern Adriatic Sea. Grain-size analysis of shoreface deposits sampled above the transgressive ravinement surface across the northern Adriatic shelf indicate a distinct relation between the sediment grain size and the rate of sea-level rise during deposition, which implies that progressive sorting must have been highly effective.

Coastal Evolution, Hydrothermal Migration Pathways and Soft Deformation along the Campania Continental Shelf (Southern Tyrrhenian Sea): Insights from High-Resolution Seismic Profiles

“…The elaboration of two isopach maps representing, respectively, the paralic/deltaic and marine lithosomes (U3 and U2) composing the transgressive wedge, enabled observations on the depocentres modifications, which occurred during the latest sea level rise ( Figure 11). As reported for similar deposits all over the world, we assisted with a general shore retreat and a main landward shift of the coastal systems [15,57,[80][81][82][83]. Furthermore, a southward migration of the river mouth, as suggested by the different distribution of the shallow-marine depocentres (U2) with respect to the paralic/deltaic ones (U3), suggests channel mobility processes at the river mouth.…”

Bathymetry of the Adriatic Sea: The legacy of the last eustatic cycle and the impact of modern sediment dispersal

“…The valleys are up to 20 km long, several hundred metres wide and up to 10 m deep. These features represent coastal environments under the influence of fluvial discharge progressively drowned by postglacial sea level rise (Storms et al, 2008).…”

Late Pleistocene Post-Glacial Sea Level Rise and Differential Preservation of Transgressive “Sand Ridge” Deposits in the Adriatic Sea

“…Only on the Adriatic shelf north of the MAD is the progressive sea level rise recorded by the back-stepping of barrier-lagoon systems [70][71][72]. On the Adriatic shelf south of the MAD, the TST is characterized by the stacking of three distinct units [66,[73][74][75] (Figure 3).…”

“…Around Gargano Promontory, this depositional break is marked by the TSR deposits rimming the shelf edge. With the exception of the North Adriatic barrier-lagoon systems, actually keeping up with, and migrating during the early to middle phase of the sea level rise [72], the South Adriatic TSR deposits represent the only near-shore, sand prone deposit surviving transgressive ravinement during the post-glacial sea level rise.…”