BSRs levels in the west Antarctic Peninsula margin: an inventory of seismic indicators of marine gas hydrates

Abstract

European Conference on Gas Hydrate (ECGH 2022), 13-16 June 2022, LyonIn the frame of ICEFLAME project (PID2020-114856RB-I00, Spanish Ministry of Science and Innovation), an inventory of BSRs levels in the west Antarctic Peninsula margin has been carried out. The aim of this inventory is to assess the theoretical transient state of these geological structures due to the global ice-sheet retreat in the Polar Regions.In the west Antarctic Peninsula margin, three areas with characteristics BSR levels have been found: (i) north South Shetland Islands (reported in previous studies, (ii) North Bransfield Island (Bransfield Strait, AP margin), and (iii) Anvers Island (AP margin). North of the South Shetland Islands, BSR levels had been reported in between the Elephant–King George islands accretionary wedge sector (Lodolo et al., 1993). Two extensive and discontinuous BSR levels (named BSR-1 and BSR-2) have been mapped in the inventory. The BSR-1 appears as local, disconnected and discontinuous patches, about 10 km diameter in geographical extension, of high amplitude reflections of inverse polarity. Its burial depth ranges from ca. 150-200 ms TWT (at the base of the accretionary wedge) to ca. 300 ms TWT (in the middle slope). BSR-2 shows more extensive spatial continuity than BSR-1. BSR-2 levels are well-defined high amplitude reflections of inverse polarity. They simulate the seafloor increasing the burial-depth with water depth from ca. 250 ms TWT in the upper slope to ca. 1s TWT at the base of the accretionary wedge. North off Bransfield Island, BSR levels had been reported in the distal continental shelf of the Antarctic Peninsula margin (Oliveira, 2017). The BSR in this area constitutes a continuous high amplitude reflection of inverse polarity. It shows a shallow and homogeneous burial depth ranging from 145 to 170 ms TWT. South of Anvers Island, a BSR level had been reported to the west of the island in the middle continental shelf of the Antarctic Peninsula margin (Solovyov et al., 2017). Here, the BSR forms an isolated patch of ca. 13 km of extension at a burial depth of ca. 150-200 ms TWT. It shows high amplitude, inverse polarity and a clear cross cutting character. All of the above BSR levels seem to be in a transient state with respect to their theoretical locations calculated from both pure methane and thermogenic compositions. We put forward two hypothesis for such situation: isostatic rebound and tectonic uplift and/or the presence of overpressured sediments. References Lodolo, E., Camerlenghi, A., Brancolini, G., 1993. A bottom simulating reflector on the South Shetland margin, Antarctic Peninsula. Antarct. Sci. 5. https://doi.org/10/bfcb22 Oliveira, M.L.L., 2017. Tectonic Characterization of the Central Bransfield Strait Using Seismic Reflection Data, Degree of Bachelor in Geophysics. Universidade Federal Fluminese. Instituto de Geociencias., Niterói – RJ, Brasil. Solovyov, V.D., Levashov, S.P., Yakimchuk, N.A., Korchagin, I.N., Bozhezha, D.N., 2017. The experiment of integrated mobile technologies used for deep hydrocarbon accumulation prospecting and geophysical mapping at the West Antarctic bottom structures. Geofiz. Zhurnal 39, 123–143. https://doi.org/10/gm8mf7Peer reviewe