GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 3.1 33 Taner, M. T., Koehler, F. and Sheriff, R. E.; 1979: Complex seismic trace analysis . Geophysics, 44 , 6, 1041-1063. Thomson, K.; 2007: Determining magma flow in sills, dykes and laccoliths and their implications for sill emplacement mechanisms . Bull. Volc., 70 , 183-201. Thomson, K. and Schofield, N.; 2008: Lithological and structural controls on the emplacement and morphology of sills in sedimentary basins . Thomson, K., Petford, N. (Eds.), Structure and Emplacement of High-Level Magmatic Systems. Geological Society, London, Special Publication, 302 , 31-44. White, R.E.; 1991: Properties of instantaneous seismic attributes. Geophysics: The leading edge of exploration, 26- 32. Yushun, D., Zhaoquan, P., Lingbang, Z. and Mingbo B.; 2011: Carbonate reservoir and gas-bearing property detection using sweetness . SEG San Antonio 2011 Annual Meeting, 1197-1201. Zhang, L., Gao, R.X. and Lee, K.B.; 2006: Spindle Health Diagnosis Based on Analytic avelet Enveloping . IEEE Transactions On Instrumentation And Measurement, 55 , 5, 1850-1858. SEISMIC ANALYSIS OF A BSR IN THE DOVE BASIN (SOUTH SCOTIA SEA) A. Mocnik 1 , D. Civile 2 , A. Del Ben 1 , R. Geletti 2 1 Dipartimento di Matematica e Geoscienze, University of Trieste, Italy 2 OGS, Trieste, Italy Introduction. In this paper we report the results from the seismic analysis of the part of the seismic profile IT95-167 that crosses a main part of the Falkland Plateau (Del Ben and Mallardi, 2004), the Dove Basin, located in the south Scotia Sea, with a N-S direction (Fig. 1). This analysis shows the presence of a high amplitude reflector that cuts the folded reflections related to the sedimentary infilling of the Dove Basin and mimics �� the shape of the seafloor. This Bottom Simulating Reflector (BSR) lays at about 750 ms. TWT below the seafloor, which is at a depth of more than 4200 m. The Dove Basin is an oceanic basin bordered by the Pirie and Bruce Banks, respectively to its west and east margins, and by the continental slope of the South Scotia Ridge, to the south. It �� shows a roughly sigmoidal shape with an abyssal plain characterized by an average depth of about 3500 m. A prominent NNE-SSW elongated ridge (Dove Ridge), about 50 km long, is positioned in the central part of the basin and it is considered as an extinct spreading centre (Eagles et al. , 2005; Galindo-Zaldivar, 2014). The seismic facies and the geometrical setting of the anomalous reflector identified suggested us to explore the origin of this BSR. Somoza et al. (2014) highlighted the presence of BSRs at three different levels in the Scan Basin located immediately to the east of the Bruce Bank. The authors interpreted the two deeper BSRs as fossil diagenetic fronts caused by elevated geothermal gradients respectively during the early and the middle Miocene; while the shallowest BSR would be originated by the presence of gas hydrates. The presence of the seismic anomaly observed in the Dove Basin could be related to: 1) presence of Opal-A/Opal-CT transformation associated to a fossil diagenetic front; or 2) presence of a gas hydrate BSR in the Dove Basin. This second hypothesis should suggest the presence of abiogenic gas, derived by the serpentinization of basaltic rocks (Rajan et al. , 2012), which compose the oceanic basement of the Dove Basin. 1) Fossil diagenetic fronts are due to several varieties of silica minerals: amorphous quartz (opal-A), cryptocrystalline quartz (opal-CT/-C) and microcrystalline quartz (chalcedony, quartzine, etc). At low temperatures opal-A is generally precipitated inorganically or biogenically fromnatural aqueous solutions. During diagenesis siliceous deposits undergo mineralogical changes from opal-A to opal-CT/-C to microcrystalline quartz (Flörke et al. , 1982). This results in a density increase across the interface between the two forms of opal, producing a strong reflection with a positive polarity. This reflection follows