Seismic study of the structure, stratigraphy and evolution of the Ross Sea (Antarctica)

On the basis of a large dataset of seismic lines performed by Italian geophysical expeditions, the regional structure and stratigraphy of the Ross Sea Embayment area in Antarctica have been reconstructed. The tectonic and seismostratigraphic conditions of the explored area are illustrated by numerous interpreted seismic lime examples distributed on all the most important existing regional features. Three seismic horizons have been interpreted and mapped over the whole Ross Sea area imvestigated: Base Plio-Quaternary (Horizon "A"), Top Oligoceme (Horizon "M") and Acoustic Basement (Horizon "S"). Moreover four other useful horizons have been locally identified and are given in specific figures to show the sedimentary cycles of the area. Isopach of the total sedimentary cover is also presented as a useful document for basin analysis and evaluation of the tectonically controlled deposition. The present paper updates with more controlled details the structural setting of the basement and sedimentary cover of the whole Ross Sea Embaymemt area. Sophisticate reprocessing of some segments or entire key lines gave much more seismic definition of basement shape and of sedimentary macro-cycles associated with rift phases. Seismic stratigraphy and fault-pattern analysis indicated that three distinct tectonic phases stretched the lithosphere of the area. An Early Rift Phase in the Mesozoic (Upper Jurassic-Lower Cretaceous) generated the first troughs of the Eastern Basin, Central Basin and Victoria Land Basin which then began to trap sediments. In the Victoria Land Basin it also seems possible to distinguish an older deposition interval of supposed Paleozoic age. During these depositions the Central High and Coulman High remained emergent. A second Main Rift Phase of Paleogene age determined a generalized crustal stretching with accentuation of the previously created troughs and highs and deposition of a relatively thick tectono-sedimentary cycle that at the end completely covered the Embayment area. The Late Rift Phase of the Neogene. Quaternary affected almost exclusively the Western Victoria Land area (Discovery Graben), while in the remaining part of the Ross Sea Embayment, a foundering process and flat sedimentary deposition due to thermal subsidence and isostatic adjustment continued.The deformation pattern of the whole Ross Sea region seems to indicate that the lithospheric stretching is due to a general transtensive process with the creation of combined distensive and strike-slip faults. From seismic exploration of the basement, a total cumulative elongation of about 130 km (from an initial 830 km to a final 960 km) for all three phases has been calculated. Special processing with an innovative dereverberation technique showed a clear Moho discontinuity signal on a seismic lime crossing the Coulman High.