GNGTS 2013 - Atti del 32° Convegno Nazionale

Neotectonic reactivation of Meso-Cenozoic structures in the Gulf of Trieste and its relationship with fluid seepings M. Busetti 1 , F. Zgur 1 , M. Vrabec 2 , L. Facchin 1 , C. Pelos 1 , R. Romeo 1 , L. Sormani 1 , P. Slavec 3 , I. Tomini 1 , G. Visnovich 1 , A. Zerial 3 1 OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Italy 2 Faculty of Natural Sciences and Engineering, University of Ljubljana, Slovenija 3 Harpha Sea d.o.o. Koper, Slovenija Introduction. In 2005 and 2009 the Italian part of the Gulf of Trieste was investigated by geophysical survey, which provided insight into the deep structure and stratigraphy of the area, and also suggested the possibility of recent tectonic activity (Busetti et al. , 2010a, b). The existing survey was recently extended to Slovenian waters with the 2013 multichannel seismic and high resolution seismic data, collected in Italian - Slovenian collaboration. The complete datas et al lows the correlation of offshore geological structures with the structures that are exposed in the coastal part of the Istria peninsula. The seismic profiles provide evidences of not only of the deep structure, but also of neotectonic deformation that drives, along the main active fault zones, the migration of fluids, such as biogenic gas seeping and thermal springs. Geological setting. The Gulf of Trieste and the surrounding coastal areas belong to the northern part of the Adriatic Foreland, consisting of the Mesozoic-Paleogene carbonate platform, overlaid by Eocene turbidites, and buried below the Plio-Quaternary marine and continental sediments of the Friuli Plain and the Northern Adriatic Sea. During the Jurassic rifting the extensive carbonate platform of Triassic Dolomia Principale fragmented into separate paleogeographic units. In the Belluno Basin to the west, deepwater carbonates (Jurassic-Cretaceous) were deposited, followed by the Scaglia Alpina marly limestones (Eocene-lower Aptian), and Gallare Marls (Eocene) which filled the basin. In the east, the Friuli Carbonate Platform, a northern part of the Adriatic carbonate platform, persisted until Cretaceous. In the Tertiary Dinaric and Alpine compressive phases, the carbonate platform was flexured and buried by Eocene turbidites (Flysch) and by Late Miocene continental and coastal Molassa deposits. During the Messinian marine regression the subaerial exposure and erosion produced complex morphology with valleys and ridges. In the western part of the Gulf of Trieste, Pliocene marine progradation draped the Messinian erosional topography with marine sediments, followed by further regression in the Late Pliocene. In the Pleistocene regression and transgression cycles, forced by glacial and interglacial periods, the alternation of marine, transitional and continental sediments was deposited (Busetti et al. , 2010a, b). The pronounced NW-SE-trending structural grain of the area is defined by compressional structures of the Dinaric fold-and-thrust system. The main structure is the topographically prominent Dinaric frontal ramp, running along the north-eastern coast of the Gulf. Belonging to the same system structural system is the Palmanova Thrust in the Friuli Plain and its eastward continuation along the north-eastern boundary of the Istria Peninsula (Busetti et al. , 2010a, b; Placer et al. , 2010). The foredeep in front of the ramp has been inverted by compressional tectonic, with thrusts dissecting and deforming the Flysch, such as the Buzet and Buje thrusts that were mapped onshore (Placer et al. , 2010). The main detachment of this frontal thust system is following the contact of Flysch with the underlying carbonates (Busetti et al. , 2010a, b). The seismic dataset. The offshore geology of the Gulf of Trieste has been investigated in several geophysical surveys. In the Italian part of the Gulf, in 2005 and 2009 were acquired 524 km of multichannel seismic (MCS) and high resolution Chirp profiles. The 2013 survey in Slovenian territorial waters, done in collaboration with the University of Ljubljana and the 29 GNGTS 2013 S essione 3.1