GNGTS 2013 - Atti del 32° Convegno Nazionale

Zanferrari, 2008). In the MCS collected in the gulf, the Carnian Unconformity is a prominent, well-defined reflector, and is also the lowest interpretable horizon, occurring at about 1.8 - 2.0 seconds. The Friuli Carbonate Platform developed mainly in the Mesozoic. During the Paleogene, carbonate deposition occurred locally in intraplatform basins, as documented by the Grado-1 well that recovered about 400 meter of Paleogene limestones, similar to those present on land in the Karst and Istria (Cimolino et al. , 2010). On the seismic reflection profiles from our study area, several kilometres wide tectonically-controlled intraplatform basins occur, filled by well- stratified horizons (Fig. 2). TheMesozoic extensional phase with NW-SE oriented extensional faults is still recognizable at the paleomargin of the carbonate platform, in the western part of the Gulf of Trieste. The tectonic structure of the margin-slope carbonate system is characterized by the master normal fault verging westward, associated with antithetic east-verging normal faults exhibiting block rotation and syntectonic sedimentation. The south-westward propagation of the Dinaric thrust system that started in the late Cretaceous reached the study area in the Eocene. The foredeep of the External Dinarides thrust system was filled by the turbidites of the Eocene Flysch. Presently the Dinaric frontal ramp is located at the coastline, where it is called the Trieste Thrust, that involves both the carbonates and the overlying Flysch with a vertical component of displacement exceeding 1000 m (Busetti et al , 2010a, b). North-westward contination of this structure, covered by the Plio-Quaternary sediments of the Friuli Plain, is the Palmanova Thrust, that is separated from the Trieste Thrust by the sinistral Sistiana Fault. The Palmanova Thrust originated in the Dinaric thrusting episode and was subsequently reactivated as a frontal structure of the Late Cenozoic South Alpine thrust system (Poli and Zanferrari, 2008). South-eastward into Slovenia and Croatia, the Dinaric frontal ramp continues into the Črni Kal Thrust (Placer, 2008; Placer et al. , 2010). The foredeep was affected by compressional tectonic, producing a series of folds and thrusts in approximately NW-SE orientation, with the detachment level at the top of carbonates (Busetti et al. , 2010a, b). A post-thrusting tectonic phase produced subvertical transpressional Fig. 2 – Multichannel seismic profiles across the intraplatform basin filled by Paleogene carbonate recovered in the Grado-1 well. The tectonically controlled basin is filled by well stratified limestones. In the post Miocene the faults were reactivated in a transpressional style. The fault strands disrupted the Messinian-Pliocene unconformity with 10-20 meter of vertical displacement. Above the fault zones, the Quaternary sediment have low amplitude signals, suggesting pervasive occurrence of fluids seeping through fracture zones. 31 GNGTS 2013 S essione 3.1