Meso-Cenozoic seismic stratigraphy and the tectonic setting of the Gulf of Trieste (northern Adriatic)

The Friuli Plain - Gulf of Trieste area is the foreland of both the East/West Alpine and North-West/South-East External Dinaric chains; it presents a flexure in correspondence of the Mesozoic carbonate Friuli Platform. The geological setting is quite well known on land, on the contrary it is poorly investigated offshore. In June 2005, 150 km of multichannel seismic and gravity profiles have been acquired by R/V OGS Explora in the Gulf of Trieste together with 37 km of multichannel seismic profiles from the inner to the external part of the Grado and Marano Lagoon. Seismo-stratigraphic analysis provides new insights into the Mesozoic carbonate Friuli Platform geological setting, in particular: a) the NW-SE orientation of the shelf margin; b) the presence, at the Friuli Platform margin, of carbonate highs of about 500 m and 350 m below sea level in the Gulf of Trieste, as a consequence of the southward shallowing trend of the shelf margin; c) the flexuring and gentle folding of the overall Friuli Platform that reaches depths of more than 1200 metres at the front of the Karst. The seismic profiles do not show evidence of reverse faults with significant vertical throw in the carbonate sequence, but it can be inferred that the Karst coastal front, up to 2-3 km offshore, constitutes the accommodation zone of the Dinaric thrust system with about 1400 m of vertical displacement. Moreover, in the Gulf of Trieste, a compressional tectonic structure with Dinaric orientation, is linked to the NW-SE thrusts and folds of the Tinjan Structure presents on land where the Flysch outcrops. The Friuli Platform flexure is testified also by indicative Bouguer gravity anomalies, with positive values in correspondence of the carbonate highs, and negative values at the Dinaric thrusts front.