GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 3.1 551 migration where we repacked the horizons and computed new inversion to update the model (Fig. 3). For each line, we obtained two models with their corresponding 2D velocity profiles. 1) The first model was obtained from sequential tomography (horizon by horizon) and it was corrected by the picked horizons in the migrated profile. We reconstructed six surfaces: sea bottom, 4 intermediate horizons and the basement. A visible velocity increase is observed from the sea bottom to the basement and from sea to the land, due to the ice sheet compression. 2) The second model was derived from the first one but including the RSU6 which is one of the principal unconformity in the Ross Sea. We differentiated these two models because the estimate of RSU6 has low reliability due to multiple interference. Conclusions . Sediments below RSU6 present high velocity consistently with their deep location in the sediment column: the deepest sediments are also generally the most consolidated due to fluid loss, diagenesis and the overall overburden sediments load. RSS-2A is characterized by high P-waves velocity and high frequency RSS-2B has velocity lower than RSS-2A. RSS- 2C and RSS-2D have lower velocity than the other two sub-sequence. From the tomographic results we observed an evident increase of seismic velocity below an intermediate surface (the fifth horizon in Fig. 3) between RSS-2A and RSS-2B which can indicate glacial sediments over-compaction by grounding ice sheet, before ice sheet retreat (Fig. 3). These interpretation is consistent with the seismostratigraphic analysis and lithological information from DSDP site 270. References Anderson J.B., 1999; Antarctic Marine Geology; Cambridge University Press, 28 September 1999 Bӧhm G., Rossi G., 2005; 3D Depth interface estimate in travel time inversion from reflected and refracted arrivals; EAGE 67th Conference & Exhibition – Madrid, Spain, 13-16 June 2005 Cat3D User Manual v 4.0, December 2012 Course note series, vol. 3. SEG — Society of Exploration Geophysicists. De Santis, L., Anderson, J.B., Brancolini, G., Zayatz, I., 1995. Seismic record of the late Oligocene through Miocene glaciation on the central eastern continental shelf of the Ross Sea. Geology and Seismic Stratigraphy of the Antarctic Margin. In: Cooper, Alan K., Barker, Peter F., Brancolini, Giuliano (Eds.), Antarctic Research Series, vol. 68. AGU, Washington, D.C, pp. 235–260. De Santis, L., Prato, S., Brancolini, G., Lovo, M., Torelli, L., 1999. The Eastern Ross Sea continental shelf during the Cenozoic: implications for the West Antarctic Ice Sheet development. Glob. Planet. Change 23, 173–196. Hayes D.E., Frakes L.A., 1975; Initial Report of the Deep Sea Drilling Project ; Vol.28, U.S Government printing Office, Washington, DC. Kraus C. et al. , Late Oligocene to early Miocene glacimarine sedimentation of the central Ross Sea and implications for the evolution of the West Antarctic Ice Sheet. AGU poster 2015 Vesnaver A., Bӧhm G., 2000; Staggered or adapted grids for seismic tomography? The Leading edge, 9, 944-950 Zecchin M., Catuneanu O., Rebesco M., 2015; High-resolution sequence stratigraphy of clastic shelves IV: high- latitude settings; Marine and Petroleum Geology 68 (2015) 427-437. Fig. 3 - Velocity model obtained from the picked horizons in the migrated profile, line BGR80-007A.