GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 3.1 549 area around drill sites across a seismic data grid helps to reconstruct the evolution of the ice sheet dynamics, by distinguishing ice proximal versus ice distal facies. Geological setting . The Ross Sea (Fig. 1) is part of the west Antarctic Rift System, that has evolved in different stages. The water depth is unusually large and may reach 1000 m in the inner shelf. The continental shelf presents a landward inclination due to the advance and retreate of the ice sheet. Three main depocenters was recognized: the Eastern Basin, the Central Trough and Victoria Land Basin. The Eastern Basin contains a thick sedimentary sequence, up to 6000 m, that is a direct record of the WAIS (West Antarctic Ice Sheet); it has not been influenced by ice streams draining the EAIS (East Antarctic Ice Sheet) and by tectonics after the early stages of its formation. Only one site, DSDP 270 was drilled in the Eastern Ross Sea, and recovered glaciomarine sequences ranging from upper Oligocene to early Miocene, with a thin cover of Pleistocene sediments. Erosional hiatuses do not allow a continuous stratigraphic reconstruction of the Easter Basin depositional history, however multichannel seismic reflection integrated the DSDP270 drilling data and help to better understand the origin and the depositional setting of the Ross Sea sedimentary sequences and unconformities (Anderson, 1999). Seismostratigraphy. Five unconformities (RSU) have been recognized in the seismic lines bounding five seismic sequences (RSS) (De Santis et al. , 1995,1999). RSS1 is made by discontinuos, subhorizontal, low amplitude reflectors, that fills tectonic and erosional basins. The seismic horizons of this unit onlap on the basement and are truncated by the Ross Sea Unconformity (RSU6). RSS-2 is characterized by three subsequences that show from the older to the younger: RSS-2A has a prograding wedge geometry, with discontinuous and low amplitude seismic reflectors, downlapping on RSU6 and cut by a sharp erosional surface. RSS- 2B is an aggrading unit thinning seaward made of high amplitude more laretally continuous, subhorizontal strata, downlapping on the red unconformity on top of subsequence RSS-2A. Fig. 1 - Ross Sea bathymetry map.