Palaeoenvironmental significance of a benthic foraminiferal fauna from an archaeological excavation in the Lagoon of Venice, Italy

An archaeological excavation at S. Francesco del Deserto Island in the Lagoon of Venice has revealed a lagoon sedimentary sequence containing the remains of a settlement from the 5th century. From this sequence, 11 samples were obtained and their foraminiferal content analysed. A statistical analysis of the relative foraminiferal abundance for different total counts has indicated that, even in palaeoenvironments, about 300 individuals form the optimal assemblage for a quantitative study. Cluster analysis applied to the optimal benthic assemblage has identified four foraminiferal biotopes in the sedimentary sequence. The foraminiferal faunas do not appear to be affected by post-depositional dissolution of the calcareous tests. arison with the present day faunas suggests that the site evolved from lagoonal conditions to salt marsh conditions. The salt marsh environment, which forms the base of the old settlement, is followed by another period of lagoonal conditions before forming the present day Island of S. Francesco. The presence of a salt marsh morphology, which defines the palaeo sea level, together with the paving of the 5th century settlement, indicates an average rate of subsidence of 1.37 mm/yr for the last 15 centuries.