Reconstruction of Holocene palaeoenvironment and sedimentation history of the Ombrone alluvial plain (South Tuscany, Italy)

The late Holocene sedimentological and palaeoecological evolution of the Grosseto alluvial plain was studied. About one hundred boreholes were drilled, following a 6-km long NW/SE transect. The lithology of the upper 9 m was studied and a reconstruction of environmental changes was undertaken based on palaeoecological macro- and microfossil analysis. Local environmental conditions around the site changed from a brackish-marine environment, which persisted until 2800 cal yr BP, when temporarily fresh-water conditions prevailed. A renewed marine influence led to the development of salt marsh conditions. A second short period of fresh-water conditions is reflected from the record from near the top of the boreholes. Mean sedimentation rates were in the order of 0.76 mm/yr before human impact and subsequently rose to ca. 1.1 mm/yr. There is evidence for a temporary cessation of sea-level rise shortly after 2800 cal. yr BP, which may be linked to cooler, wetter climatic conditions and a decline of solar activity. Thermal contraction of ocean water during the early Subatlantic may have played a role.