Latest Holocene depositional history of the southern Venice Lagoon, Italy

Abstract

Analyzing the signatures of landscape changes in the stratigraphic record is crucial to refine our knowledge of tidal landform dynamics and represents a first step toward the development of predictive morphodynamic models. The southern Venice Lagoon (Italy) is particularly suited to analyze modifications in the depositional environment and, consequently, in the sedimentary record because of the remarkable changes that occurred in the last centuries. We collected 25 cores along a NE–SW linear transect about 5 km long cutting through salt marshes, tidal flats, and subtidal platforms. High-resolution sedimentological analyses defined the spatial arrangement of four deposits along the transect (palustrine, salt marsh, lag, and tidal-flat/subtidal-platform deposits), whose cores were dated through radiocarbon, 210Pb, and 137Cs geochronological analyses. The study succession testifies an evolution from a palustrine freshwater environment to a lagoonal environment over the last 2000 years. The palustrine peat progressively evolved into salt marshes in the 14th century. Salt-marsh aggradation is characterized by different accretion rates over time and occurred in parallel with the decrease in the salt-marsh extent and tidal-flat expansion. Where salt-marsh deposits were locally flooded and impacted by wind waves, a lag deposit developed. As a consequence of the progressive water deepening, organic-rich mud accumulated above the lag. The results, as well as providing the first accretion model for the latest Holocene succession in the southern Venice Lagoon, highlight that the disappearance of salt marshes in this area has to be ascribed to the lateral erosion of their margins, rather than to their progressive drowning.