Holocene evolution of the Northern Adriatic Platform: morphologic and stratigraphic evidence

The northernmost part of Adriatic Sea lies between Istria, Karst and the Friulian Plain and it is divided between Italian, Slovenian and Croatian waters. A robust chrono-stratigraphic framework of the Northern Adriatic shelf was supported by the geophysical, bathymetric and stratigraphic data collected during cruises VE2004, VE2005 and RISA2009, that led to the production of the geological map of the Italian seabed. Moreover, in the last years Harpha Sea Inc. carried out a multibeam bathymetric survey of the Slovenian waters, leading to the production of a very high-resolution DEM. This was a key tool for understanding the sea-floor morphologies. During cruise NAD2012 the oceanographic vessel “Urania” surveyed the Italian and Slovenian shelf, acquiring 750 km of CHIRP-sonar seismo-acoustic profiles and 10 gravity cores. These new data allowed for the first time to observe in continuity the transition from the rocky coast of Istria to the Friuli plain. The area between Monfalcone and Piran Bay is characterized by a mud-dominated body, consisting of Holocene marine deposits, with a maximum thickness of about 25 m in Piran Bay and that thins toward the Friulian coast, where the delta system of Isonzo River (Soca in Slovenian) is present. The marine sediments seal the alluvial plain that characterized the area until ca. 7.5 ka BC, when sea-level rise led the Adriatic to re-occupy the Gulf of Trieste. The ancient alluvial plain is characterized by a complex network of fluvial ridges fed by the valleys draining Karst and Istria; moreover, DEM highlight an incised meandering paleochannel, recognizable from the Italian shelf to Koper Bay. The evolution of the Trieste Gulf was constrained by a main morphologic threshold corresponding to the deep morpho-structural depression existing in front of Savudrija Promontory. Some very large submarine dunes are connected to this incision.