Evoluzione tardopleistocenica-olocenica del delta del F. Tagliamento e delle lagune di Marano e Grado (Golfo di Trieste)

Abstract

The recent evolution of the coastline of the Friuli-Venezia Giulia has been under study since 1976. All the collected data on radiocarbon age (14C) are analysed and reported in this paper with the aim to update the already acquired knowledge. During the last stage of the Wormian glaciation (22,000 to 18,000 yrs B.P.), the Gulf of Trieste was a vast alluvial plain, with a steppe vegetation, characterized by heavy supply of the Isonzo-Natisone-Torre systems on the East and of the Tagliamento River on the West The alluvial phase in the upper paleoplain ended during the Postglacial period; the rivers cut through their old deposits and carried the eroded sediments to the lower plain, whereas the southernmost area of the Adriatic paleoplain began to be progressively submerged by the sea. During the postglacial transgression, because of the paleoplain slope, the sea first reached tha Istrian coast (10,000 yrs B.P.), then the Carso coastline of Trieste and only recently the Veneto-Friuli lower coast The action of the Tagliamento River was so strong here, that the river eastwards and opened an outlet into the pre-existing Marano lagoon present in that area for at last 5,540 yrs, and developed its delta over a period of 2,000 years. Further eastward the Marano lagoon gradually evolved, moving over the adjacent alluvial plain and reaching a configuration very similar to the present one as early as 1,400 years ago. Further eastwards again, the Grado lagoon area was still dry land when the western delta and the lagoon environments had already formed. The Grado lagoon is in fact 4,400 years younger than the Marano lagoon and 900 years younger than the Tagliamento delta. Its western part developed in late-Roman times, the eastern part is even more recent as it dates back to the last diversion eastwards of the Isonzo River, which occurred between the 9th and the 18th century A.D.