Environmental evolution of the Marsala sound, Sicily, during the last 6000 years

Fossil molluscan assemblages from 12 radiocarbon-dated short cores have been considered and integrated with information from archaeology, tectonics, and relative sea-level change in order to define the Holocene evolution of the Stagnone di Marsala, a sound along the western coast of Sicily that experienced at least 3000 years of human impact, since the Phoenician times. During the considered time span, we have no evidence of emersion, though the occurrence of a very restricted circulation is recorded at the base of very shallow cores dated 1240 +- 50 and 1560 +- 40 years BP. We hypothesise that the Phoenician road, now submerged, connecting the Island of Mozia with the Sicilian mainland, was critical in isolating a marshy environment along the southeastern coast of the Stagnone before about 1600 years BP. Our cores show that the molluscan association typical of the superficial muddy sand in sheltered areas (SVMC) has been always dominant at the basin scale, conformably to the present-day situation. Multivariate statistical analyses were performed on abundance data of molluscan associations resulting in four clusters that describe different aspects of the SVMC biocoenosis: the first characterised by the sediment-related SVMC species, and the other three associated with a more mud-rich sediment, with a prevalence of taxa related to the leaf stratum of Posidonia, Cymodocea, or to seaweeds. In contrast with the present-day situation, we record a past occurrence of Posidonietum in the northern basin at about 3600 years BP, corresponding to a period of more open circulation. This phenomenon was induced by channels, now closed by saltworks, that cut the present-day Isola Grande into islets.