GNGTS 2015 - Atti del 34° Convegno Nazionale

34 GNGTS 2015 S essione 3.1 an isothermal surface, mimicking and crosscutting the reflectors of the stratigraphic succession. 2) The gas-hydrate BSR displays high seismic amplitude with reverse polarity often accompanied by lowered frequency (low-frequency shadow) due to attenuation by free gas (Vanneste et al. , 2002). On a global scale, abiotic or abiogenic CH 4 is produced inmuch smaller amounts respect biogenic CH 4 , and is generally not recognized in economically exploitable reservoirs. In many geological environments, biotic and abiotic gases are mixed, and in many cases it is not easy to distinguish them. From scientific literature, magmatic process and gas-water-rock reactions trigger the production of abiotic CH 4 (Etiope and Sherwood Lollar, 2013). The most widely abiotic CH 4 generation mechanism in natural settings is the serpentinization of ultramafic rocks. The two options presented are both compatible with the few available data on the geothermal gradient in the south Scotia Sea (yield values of 86.89 mW/m 2 at 2918 m water depth in the Scan Basin, Barker et al. , 2013). During the year 2013, a sub-project has been presented and funded by the PNRA to explore these alternative possibilities in the context of the project VALFLU. Geological setting. The Scotia Sea region is mainly of oceanic crustal structure and origin. It is bounded by the Drake Passage to the west and by the Scotia Arc on three sides. The Scotia Arc consists of the North and South Scotia Ridges, which are an assemblage of islands, submarine fragments of continental crust and deep basins, and of the South Sandwich island arc to the east. Oceanic magnetic anomalies suggest an Oligocene–Early Miocene age for the first sedimentary unit covering the basement of the Scotia Sea (Maldonado et al. , 2006). Lindeque et al. (2013) highlighted a diachronic opening �� ��� ������ ��� ���������� ����� ��� ������ ���� ����� �� ���� in the Scotia Sea (17.3–12.0 Myr): the oldest part would be near the Antarctic Peninsula, while toward northwest it becomes younger� ��� ���� ����� �� � ����� . The Dove Basin is a small NNE-SSW oriented sigmoidal depression located in the South Scotia Ridge. It is positioned between 60.5 and 58.5° S, and between 45 and 40° W, about 200 km long and 150 km wide. A NNE-SSW elongated ridge (Dove Ridge), about 50 km long, occupies the central part of the basin, where MORB-type tholeiitic basalt rocks have been recovered. In the basin depocenter, the sedimentary succession overlying the oceanic basement reaches more than 1.5-s TWT. Fig. 1 – Physiographic map of the southern margin of the Scotia Sea, with the indication of the principal banks and basins. The study area is in the white circle.