GNGTS 2008 SESSIONE 3.2 Braitenberg, C., S. Wienecke, and Y. Wang (2006), Basement structures from satellite-derived gravity field: South China Sea ridge, Journal of Geophysical Research, Vol.111, B05407, doi:10.1029/2005JB003938. Braitenberg, C. and J. Ebbing (2007), The gravity potential derivatives as a means to classify the Barents sea basin in the context of cratonic basins, Extendended Abstracts, EGM 2007 International Workshop, Innovation in EM, Grav and Mag Methods: a new Perspective for Exploration, Villa Orlandi, Capri - Italy , 15-18 April 2007 (http://www2.ogs.trieste.it/egm2007/) Braitenberg, C., S. Wienecke, J. Ebbing, W. Born, and T. Redfield (2007), Joint gravity and isostatic analysis for basement studies - a novel tool, Extendended Abstracts, EGM 2007 International Workshop, Innovation in EM, Grav and Mag Methods: a new Perspective for Exploration, Villa Orlandi, Capri - Italy , 15-18 April 2007 (http://www2.ogs.trieste.it/egm2007/), Ebbing, J., C. Braitenberg, and S. Wienecke (2007), Insights into the lithospheric structure and the tectonic setting of the Barents Sea region by isostatic considerations. Insights into the lithospheric structure and the tectonic setting of the Barents Sea region from isostatic considerations, Geophys. J. Int., 171, 1390-1403, doi:10.1111/j.1365-246X.2007.03602.x Förste, C., Schmidt, R., Stubenvoll, R., Flechtner, F., Meyer, U., König, R., Neumayer, H., Biancale, R., Lemoine, J.-M., Bruinsma, S., Loyer, S, Barthelmes, F., and Esselborn, S., 2007. The GeoForschungsZentrum Potsdam/Groupe de Recherche de Geodesie Spatiale satellite-only and combined gravity field models: EIGEN-GL04S1 and EIGEN-GL04C. Journal of Geodesy, doi:10.1007/s00190-007-0183-8. Lane, N. (2007), Mass extinctions – reading the book of death, Nature 448, 122-125. Pavlis, N.K., S.A. Holmes, S.C. Kenyon, and J.K. Factor, An Earth Gravitational Model to Degree 2160: EGM2008, presented at the 2008 General Assembly of the European Geosciences Union, Vienna, Austria, April 13-18 (2008). Pavlov, Yu.A (1995), On recognition of rift structures in the basement of the West Siberian plate, Geotectonics, English Translation (AGU), Vol. 29, no.3, 213-223. Peterson, J.A. and J.W. Clarke (1991), Geology and hydrocarbon habitat of the West Siberian Basin, AAPG Studies in Geology # 32, pp. 96, AAPG, Tulsa, Oklahoma, Saunders, A.D., R.W. England, M.K. Reichow, and R.V. White (2005), A mantle plume origin for the Siberian traps: uplift and extension in the West Siberian Basin, Russia, Lithos, 79, 407-424. Shin Young H., H. Xu, C.Braitenberg, J. Fang, and Y. Wang (2007) Moho undulations beneath Tibet from GRACE-integrated gravity data, Geophys. J. Int., doi: 10.1111/j.1365-246X.2007.03457.x, 1-15. Vyssotski A.V., V.N. Vyssotski, and A.A. Nezhdanov (2006) Evolution of the West Siberian Basin, Marine and Petroleum Geol., 23, 93-126. Wienecke S., C. Braitenberg and H.-J. Götze (2007) A new analytical solution estimating the flexural rigidity in the Central Andes, Geophys. J. Int., 169, 789-794, doi:10.1111/j.1365-246X.2007.3396.x. DINARIC TECTONIC FEATURES IN THE GULF OF TRIESTE (NORTHERN ADRIATIC) M. Busetti1, V. Volpi1, M. Marchi1, C. Zanolla1, E. Barison2, L. Baradello1, M. Giustiniani1, D. Nieto1, R. Nicolich2, R. Ramella1, R. Romeo1, N. Wardell1 1 Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS, Trieste 2 Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Trieste Evidence of a Dinaric fault system in the Gulf of Trieste correlated to offshore structures out- cropping in the Istria Peninsula and buried below the Friuli Plain, as well as the offshore geologi- cal setting at the frontal thrust system of the Karst, have been identified in multichannel seismic pro- files acquired in 2005 by OGS Explora (Busetti et al., in press). The Gulf of Trieste area is the foreland of the NW-SE External Dinaric chains. The foredeep is constituted by the flexured Mesozoic - Paleogenic carbonate Friuli Platform (Della Vedova et al., 2008), filled by the turbidites of the Eocene Flysch formation, consequent to the Late Cretaceous - Paleogene Dinaric compressional activity. Dinaric main features are present on land: in the Karst anticline, in Istria as the Buzet thrust and in the Friuli Plain with buried thrusts, such as the Pal- manova Line, and off-shore the Trieste - Golfo di Panzano Fault. In May and June 2005, 150 km of multichannel seismic (MCS) and gravity data 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 (Fig. 1). The MCS data were acquired for a project to evaluate the geothermal resources, commissioned by the Direzione Centrale Ambiente e Lavori Pubblici – Servizio Geologico of the Regione Autonoma Friuli Venezia Giulia. The exploration wells Cavanel- la 1, Cesarolo 1, and Amanda 1 bis, together with published oil exploration seismic profiles and the 411 GNGTS 2008 SESSIONE 3.2 Fig. 1 – Position map of the multichannel seismic lines acquired by OGS Explora and top carbonate isobath map (modified after Nicolich et al., 2007). deep crustal seismic profile CROP M-18, were used for calibrating the seismic stratigraphy. The Bouguer gravity anomaly has been calculated for the Gulf of Trieste and the surrounding Italian coastal area using the OGS gravity dataset, consisting of 3833 stations. The Bouguer gravimetric anomalies have been calculated with 2,670 kg/m3 density and topographic correction distance up to 167 km from the station considering also the effect of the curvature of the earth. The Cenozoic seis- mic stratigraphy and tectonic evolution of the Gulf of Trieste have been highlighted by the results of the interpretation of multichannel seismic profiles. The Friuli Platform in the Gulf of Trieste is tilted, reaching depths of more than 1200 metres to the East at the front of the external Dinarides Fig. 2 – Multichannel seismic profile G05-4bis across the Gulf of Trieste (modified after Busetti et al., in press). 412 GNGTS 2008 SESSIONE 3.2 Fig. 3 – Multichannel seismic profile showing the dinaric fault system crossing the Gulf of Trieste (modified after Busetti et al., in press). thrusts of the Karst, and a minimum depth of 350 m in the centre of the gulf (Figs. 1 and 2). The carbonate shelf margin of the Friuli Platform presents mainly the NW-SE Dinaric trend, with minor indentations southward with a NE-SW orientation, in agreement with the saw-toothed NW-SE Dinaric and NE-SW antidinaric trends present on land. It is characterised by morphological highs, one at a depth of less than 500 m in the northern part of the Gulf of Trieste, and the second at less than 350 m further south. The depth of the highs constitutes a shallowing trend of the shelf margin from the Cesarolo and Grado Highs at about 800 m and 650 m respectively on land, to the lime- stone outcrops of the Savudrija Rticˇ in the Istria Peninsula (Fig. 1) (Nicolich et al., 2007, Della Vedova et al., 2008). In the Eastern sector of the Friuli Platform, the tectonic activity produced deformation in the car- bonate and in the Flysch sequences. On the seismic profiles, the carbonates are affected by gentle folds and faults all along the foredeep. The Flysch sequence presents the main tectonic deformation with the occurrence of an inverse fault system that produced the development of an anticline with NW-SE orientation (Figs. 2 and 3). The fault strands have up to 30 m of throw each, and SW and SE dip in the westward and eastward side respectively. The uppermost fault strands are linked to low angle deeper faults, and the top of the carbonate probably acts as detachment surface. The South-Eastern part of the tectonic Flysch feature links up to the Dinaric thrusts and folds of the Tin- jan Structure present in the Debelj Rticˇ (Istria Peninsula) where the Flysch outcrops. The spatial dis- tribution of the fault strands and the overall fold trend indicate a Dinaric orientation of the structure, hence related to this compressional phase. Eastward of the Flysch anticline, the Palmanova line was thought to continue across the Gulf of Trieste. However, no evidence of significant thrust faulting disrupting the carbonate is present in the seismic profiles. Instead, less than 2 km from the coast, the carbonate, flexured in front of the external Dinarides thrusts, reaches a depth of more than 1200 m. Considering that the hills along the coast are 100-400 metres high, 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 more than 1500 m of vertical displacement. The Friuli Platform flexure is also supported by indicative Bouguer gravity anomalies, with positive values in correspondence of the carbonate highs, and negative ones at the Dinaric thrusts front. 413 GNGTS 2008 SESSIONE 3.2 References Busetti M. Volpi v., Barison E., Giustiniani M., Marchi M., Ramella R., Wardell N., Zanolla C.; Cenozoic seismic stratigraphy and tectonic evolution of the Gulf of Trieste (northern Adriatic). Proceedings of “ADRIA 2006 – International Geological Congress on Adriatic region”, 19-20 June 2005, Urbino (Italy). GeoActa. In press. Nicolich R., Della Vedova B., Barison E., Vecellio C., Rizzetto D., Masetti D., Cimolino A., Flora O., Ramella R., Busetti M., Volpi V., Zanolla C., Cucchi F., Marocco R.; 2007. “Le acque calde della Pianura Friulana. Realizzazione della Carta Geologico- Tecnica della Risorsa geotermica regionale e definizione delle Linee Guida per il suo utilizzo”. Pubblicazione per conto della Regione Autonoma Friuli Venezia Giulia, Direzione centrale ambiente e lavori pubblici, Servizio Geologico, 27 pp.