GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.1 535 GEOPHYSICAL STUDY OF THE OTRANTO CHANNEL N. Bertone 1 , A. Del Ben 1 , G. Brancatelli 2 , R. Geletti 2 1 Dipartimento di Matematica e Geoscienze – DMG, Università di Trieste, Italy 2 Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS, Trieste, Italy Introduction. During the 2015 the OGS research vessel Explora acquired new data in the Otranto Channel - (Otranto Channel gaS Seepages, OCSS_15). The aim of this survey was to study gas seepages, to identify deep-sited coral mounds in the SouthAdriatic Sea, to relate these shallow features to the deep tectonic and morphological structures. At the depth of 900 m the OGS vessel dragged some still-living corals. This was apparently a strange recovery because these corals live below the photic zone hence, how they grow and feed also in other parts of the world has been an interesting question since few decades. There are several cases demonstrating that bio-constructor’s organisms can take advantage of natural gases to form coral banks (e.g. Hovland and Judd, 1988). Gas seepages are already known in the South Adriatic Sea (Del Ben et al. , 2011). However, is not clear the nature and location of the gas reservoirs from which these seepages origin. In the Otranto Channel the gas is mainly accumulated in huge reservoirs on the top of the Apulia carbonate platform and in some minor reservoirs dispersed in the clinoforms of the Plio-Quaternary hemipelagic successions. The peculiarity is the biunivocal relationship between coral mounds seen on the sea floor and gas seepages deriving from the deepest sectors. Methods. To highlight structures and nature of gas reservoir, we used geophysical data collected during the 2015 Explora survey and from public available data; two groups of available data. The first allows to reconstruct the deep structures and the geometry of geological formations. This dataset includes: 1) regional seismic lines with high depth of investigation (DOI) and low- resolution (MS29 and ViDEPI lines – zone F). 2) OCSS_15 seismic lines for a detailed study on the selected area: if compared to the latter they have lesser DOI and higher resolution (Fig.1). The second group is necessary to reconstruct shallower structures. This second dataset Fig. 1- a) Location map of the seismic dataset. b) Contour map of the bright spot (light blue area - values are in TWT) and Apulia Carbonate platform margin (green line) from Del Ben et al. , 2011 – modified.