LATE HOLOCENE PALAEOENVIRONMENTS AND HUMAN IMPACT IN THE ARCHAEOLOGICAL AREA OF CA’ TRON, AT THE MARGIN OF THE LAGOON OF VENICE (ITALY)

The palaeonvironmental evolution of the Ca’ Tron area, in the alluvial plain near the shores of the Lagoon of Venice, has been investigated within the framework of a geoarchaeological project started in 2000, funded by Fondazione Cassamarca. The prominent archaeological feature in the study area is a stretch of the Roman road Via Annia, built in the 2^nd century B.C., but archaeological evidences span since the Iron Age to the Middle Age. The main upbuilding of the alluvial plain took place during the last glacial maximum. The post-glacial deposits belong to the Late Holocene. In the 2^nd millennium B.C., a high energy river of alpine origin, the Piave River, crossed the study area following the course of the underground water-fed Sile River, and flowed into the lagoon. At that time, the lagoon was less extended towards the mainland. It reached the maximum estension, bordering the study area, only in Medieval times. Apart from this event, the Late Holocene palaeohydrographic network was mainly related to minor rivers originated in the plain, fed both by underground water and local runoff. They usually followed the larger, Late Pleistocene palaeochannels. Fossil pollen in the muddy, organic-rich infilling of one of these abandoned channels, the paleoalveo della Canna, has been studied. The bottom of this ca. 15 m wide and 2.5 m thick sedimentary body, has been radiocarbon dated to 795 - 390 cal BC. The sub-vertical banks and almost rectilinear planform of the palaeochannel suggest human intervention on the river, possibly already in pre-Roman times. Pollen analysis shows that during the Iron Age up to the beginning of the Roman Age the land was used for farming practices (evidences of Hordeum, Avena-Triticum, Plantago lanceolata pollen), grazing animals and cultivating fruit- and nut-bearing trees and shrubs (Juglans, Corylus, Rosaceae Maloideae, Vitis). Human activities did not reduce the broadleaf plant communities (arboreal pollen percentage ranging from 30 to 55 % of the total upland plant pollen). Aquatic plant communities were formed by typical marsh and swamp fresh-water species. The paleoalveo della Canna was crossed by the Roman Via Annia by means of a stone bridge, while in the Middle Age a small wooden bridge existed in the same location (archaeological excavations are being carried out by under the direction of F. Ghedini).