Multi-disciplinary surveys for the new geologicla maps of the low Friuli plain (Italy)

The study site is located in the central area of the Friuli Venezia Giulia (Italy) and is covered by geological map sheets 087 Palmanova and 108 Lignano Sabbiadoro. The area under consideration extends between the spring horizon to the north and Marano lagoon to the south. It covers a total area of 760 km2. The zone under consideration is characterised above all by the presence of alluvial deposits dating back to the Last Glacial Maximum (LGM; 30,000-17,000 b.C.) and by the presence of deposits originated by the activity of resurgent rivers including Stella, Zellina, Corno and Aussa. The western sector of the Lignano sheet also includes deposits that can be ascribed to the post-LGM activity of river Tagliamento (last 17,000 years). Along the coastline post-LGM deposits reach a thickness of 10 m. Along the lagoon fringe there are territories that were reclaimed in the Twentieth century where lagoon deposits outcrop. The project was conducted within the framework of the GEO-CGT by the Regional Geological Survey – DG Environment and Public Works of the autonomous region of Friuli Venezia Giulia and the University of Trieste and Udine. It involved the preparation of 1:10,000 geological maps of Friuli Venezia Giulia which integrated new geological data (surveyed and processed to this very aim) into already existing information. Reference criteria for the cartographic representation and digitalisation are those set by the Italian Government for the preparation of the new national geological cartography at a scale of 1:50,000 (CARG project). The Technical Geological Map (CGT) has been the primary source of grain-size and geotechnical information as far as the soil and the immediate subsoil of the areas taken into consideration. The bibliography collected has been integrated with the most recent studies and data on the geology and pedology of the areas involved. Also archaeological aspects have been taken into consideration to better define the history ad evolution of more recent deposits. The map representing microrelief, together with the observation of aerial photographs taken in different years and satellite images, has proven a useful tool to analyse and define the area of the most frequent morphologies connected with river erosion and deposition phenomena. This information has been subsequently cross-checked during surveying campaigns. More in detail, historic maps helped identify natural and/or man-made modifications of the hydrographic network ad of the use of soil in recent past. Some information on the age of the deposits were also taken from the numerous Roman archaeological sites present in the study areas. Field surveys were aimed at identifying geomorphological landforms and sedimentologic characteristics and at defining the age of deposits. As the areas observed are plain ones and no deep natural outcrops are present, particular attention was given to the stratigraphy of the deposits that outcrop along the walls of artificial excavations. In the areas with no significant outcrops and in the most interesting ones, borehole logging was performed by means of a manual Edelmann probe. These boreholes reached a depth of 2-3 m and sometimes 6 m. The sediment samples collected were tested for grain-size distribution and carbon-14 dating. Simultaneously, mechanical surveys were performed on the whole area reaching a depth of 10 m plus approximately a hundred static penetrometer probes reaching a 30 m depth. The comprehensive geomorphological, sedimentological and geotechnical data collected permitted to define stratigraphic units, sedimentation environments, texture of surface deposits and the main landforms that characterise the western low Friuli plain. The last surveying phase consisted in organising and processing the data collected thanks to the special functions of GIS. The entire project was conducted using a comprehensive set of hardware and software tools which permitted to maintain a close relation between the data collected on the field (database) and their digital geo-referenced map representation (geo-database). Data could therefore be viewed and interpreted according the standards set within the framework of the CARG project.