Evoluzione paleoambientale dell'area archeologica sommersa di S. Leonardo in Fossa Mala (Laguna di Venezia)

Palaeoenvironmental evolution of the Venice Lagoon: the submerged archaeological area of S. Leonardo in Fossa Mala

Abstract

Palaeoenvironmental investigation has been carried out in the sub-bottom of the submerged medieval archaeological area called S. Leonardo in Fossa Mala in the Venice Lagoon (Italy). Ten 6 m long continuous cores were obtained in the site and sedimentological, micropalaeontological and radiochronological analyses were performed in order to reconstruct the Holocene depositional history of the site. The alluvial sediments at the base of the sequence took place first as levee and crevasse splay sand, interested by a soil on the top, followed by overbank fines and crevasse splay deposits. The following lagoon beach deposits, subsequent to a sedimentary gap phase, are linked to the last marine ingression. Lagoon deposition was interrupted by a fluvial event, followed by high energy beach environment, dated back to the last phases of II millennium B.C. (2910 ± 50 years BP), and by a low energy intertidal plane. The upper part of the sequence is characterized by salt marsh environment, starting from III-IV century A.D. (1750 ± 50 years BP), an emerged area, where a Monastery was founded and inhabited from the XI century to the XIII-XIV century A.D.. The age of the salt marsh of the site is linked to a regional scale phase of low marine level and lagoon areas emersion, confirmed in Venice basin by geoarchaeological and historical data. The site, located near the bank of the important artificial channel Malamocco-Marghera, is nowadays submerged and subjected to significant erosional processes.