Late Holocene sedimentary changes in shallow water settings: the case of the Sele river offshore in the Salerno Gulf (south-eastern Tyrrhenian Sea, Italy)

Abstract

A complementary data set consisting of sedimentological, petrophysical, geochronologic and seismo-stratigraphic analysis was used to detect the sedimentary changes in the inner shelf record in a mostly stable region, over the last 3 ky cal BP, that is since the sea level attained its present day position. This study has been carried out within the VULCOST project on the Salerno Gulf (south-eastern Tyrrhenian Sea, Italy), to learn more about the impact of minor morpho-climatic changes and anthropogenic disturbances on the shelf sedimentary record. Some decimeter-thick sandy beds deposited on the inner shelf, off the Sele river mouth, in the time span corresponding to the Little Ice Age (LIA), despite the fact that, at the time, the coastline at that time was farther inland with respect to its present day position. Since the beginning of the 20th century, mainly fine grained sediment settled, possibly owing to the restoration of mild climatic conditions, changes in the rivers’ regime and land-use. The analysis of the marine cores, collected off the coast, also reveals a litho-stratigraphic mismatch among coeval intervals, possibly driven by the different response of the catchments to the morpho-climatic variations. High resolution seismic data shows that the sediment bypass area, shaped by wave action, is much deeper than the estimated limit, if computed on the base of fair-weather wave length and sedimentologic analysis. Indeed, toplap terminations of reflectors are recognizable as deep as 25 m in the southern sector of the Gulf and suggest an intense reworking of the seabed over long periods, much deeper than the outer limit of the beach. This evidence is also supported by the state of pyroclastic layers in the core record, which proves sediment reworking in the marine setting, down to 24 m of depth. The high resolution sedimentologic and stratigraphic reconstructions point to a non linear relation between depth, distance from the coast and sand deposition over the time. This suggests a complex picture of coastal dynamics within the same basin, with a remarkable outcome regarding the wave-cut terraces as proxies of sea level stands.