Holocene evolution of the Ombrone alluvial plain (Tuscany, Central Italy)

The Late Holocene sedimentological and palaeoecological evolution of the Grosseto alluvial plain (Tuscany, Italy) was studied using approximatly 120 lithological borehole descriptions, palaeoecological records and five C-14 dates. During the Holocene, the Ombrone River migrated laterally, but did not avulse. New radiocarbon dates allow average sedimentation rates to be calculated in the order of -0.9 mm/yr before 2800 cal yr BP and similar to 1.4 mm/yr between 2800 cal yr BP and the present. This is considerably lower than hitherto presumed. The new C-14 ages can be related to the relative sea-level curve for the Tyrrhenian Sea. The results of macro- and micro-fossil analysis suggest increasing human influence since similar to 2800 cal yr BP and an environmental change from brackish-marine to freshwater conditions. Recent marine influence led to saltmarsh conditions.