Geomorfologia e stratigrafia tardo-quaternaria dei fondali italiani tra Punta Tagliamento e Cortellazzo (Adriatico Settentrionale)

This work considers the north sector of the Adriatic Sea and investigates an area of circa 1200 km2 located between the Venice Lagoon and the Istrian Peninsula. In this area the maximum depth of the sea floor is less than 35 m and it has been investigated in detail for the beach nourishment of the Venetian coastline. The aim of this research is to improve the knowledge of the deposits that settled during the Last Glacial Maximum (LGM) when the coast of the Adriatic Sea was in the Mid Adriatic Depression (MAD). During that period the seafloor of the north sector of the Adriatic Sea that can be observed today was exposed to the subaerial conditions and was characterized by alluvial processes. For this purpose numerous seismo-acoustic profiles, obtained with the CHIRP technique, and two cores have been studied; these data were collected during two oceanographic cruises, VE04 and VE05, that were organised by CNR-ISMAR Bologna in July 2004 and May 2005 respectively. The initial part of the work consisted in the recognition of the main reflectors in a single CHIRP profile and then relating them to other profiles. To carry out this step, the use of a 2D/3D view was essential and that was provided by the software Move. Five units are present between the main reflectors, these are useful to find channels or other particular structures which can be related to channels, like bars or fluvial ridges. Then, using the programme SeisPhro, it was possible to pick points on the reflectors and, subsequently, recreate the surfaces made by the reflectors with the software ArcGis, a Geographic Information Sytem (GIS). The last step was to study the CHIRP profiles and to find some of the typical features of the signal that indicates the presence of fluvial channels. It has been possible to recognize four river channel belts and to observe that three of them follow the direction East-West and they are almost straight, while the last one presents an important curve. At the moment it is not possible to confirm if this last channel is related with one of the others or not, because the avaible radiocarbon datings made in the two cores can only suggest that they formed between LGM and 9.000 years ago, when the area was covered by the sea. The 14C dating was carried out on peat layers present in the cores and suggesting that the main reflectors formed slighty before and in the first part of the Last Glacial Maximum. The cores show an alternation of continental sand and peat horizons. As said previously it has been possible to recognize profiles that transversely intercept channels and this setting helps to observe and measure the width and depth of fluvial ridges and bars. A transgressive deposit has been also observed and it was recognized by the typical light CHIRP signal produced by this unit, as already highlighted in the geological sheet “Venezia” NL33-7 of the Geological Map of the Italian Seas at scale 1: 250.000. This work shows the importance and the potential of the high resolution seismo-acoustic profiles in understanding the processes that happened in the North Adriatic beetween 30.000 and 9000 years ago. Moreover this research studied an area that undergone the last phase of the post-LGM trangression and it can suggest some information about the erosive processes that the present coastline is going to experience in the next future because of the increasing sea-level river.