PUMA
Istituto di Scienze Marine     
Donda F., Brancolini G., De Santis L., Trincardi F. Seismic facies and sedimentary processes on the continental rise off Wilkes Land (East Antarctica): evidence of bottom current activity. In: Deep-Sea Research Part Ii-Topical Studies in Oceanography, vol. 50 (40429) pp. 1509 - 1527. Pergamon-elsevier Science Ltd, 2003.
 
 
Abstract
(English)
"The slope and rise areas off Wilkes Land (East Antarctica) encompass three large-scale composite sediment ridges dissected by two broad deep-sea valleys (Jussieu Canyon and WEGA Channel). Large-scale depositional architecture, revealed from multi-channel seismic profiles acquired during the WilkEs Basin GlaciAl History (WEGA) cruise, indicates a wide temporal and spatial variability in the dominant depositional processes delivering or redistributing sediments on the slope and rise. All three sediment ridges are built on a flat seafloor and resulted from the growth of a thick sediment section (at least 2 km) with a depositional relief in the order of hundreds of meters on the adjacent deepsea valleys. The sediment ridges show their maximum internal complexity in areas shallower than 3000m, where they are also substantially thicker (as much as 1-1.5 s. in two-way travel time). High amplitude sediment waves (typically 20-30m and up to 50-70m) have wavelengths ranging from 1500 to 3500m and occur in the deepest sectors of the continental rise, where the sediment ridges toe out. In the lower rise, the sediment waves display a consistent decrease in wavelength with increasing water depth. On seismic profiles, the relief of the sediment waves decreases from older to younger sequences, possibly indicating a decrease in bottom current intensity throughout their formation. Sediment waves occur also at the seafloor, which is dominated elsewhere by irregular topography and widespread evidence of erosion. However, no conclusion can be drawn on the possible modern activity of these large-scale bedforms. In shallower, upper-rise areas, where the sediment ridges are thicker, sediment waves are evident in the upper stratigraphic units, while the remaining section is characterized by the development of channel-levee complexes (seen as small-scale erosional channels, bordered by depositional reliefs consisting of variable-amplitude reflector packages wedging out away from the channels). Channel-levee complexes are locally associated with poorly developed sediment waves. The origin of these features is likely related to transport by turbidity flows from the edge of the Antarctic shelf and implies the presence of a more temperate glacial regime than the one dominating since the Late Miocene. The formation of the sediment waves, both in this more proximal area and on the deep rise, is indicative of the impact of bottom-hugging currents during intervals of the Cenozoic history of the margin. No constrains are available at present on the nature of these currents nor on the timing of their activity; down-slope turbidity currents, downwelling dense waters or slope parallel contour currents are possible mechanisms. Despite this substantial uncertainty, the observed progressive upward attenuation of the wave amplitudes indicates that substantial variations of sediment delivery and dispersal occurred through time. We suggest that the interval of more complex depositional geometry in the proximal areas reflects higher bottom current velocity and/or increased sediment input perhaps during conditions of temperate, wet-based ice sheet on the continent. These conditions were conducive to high rates of melt-water production, formation of dense plumes, and enhanced sediment input. (C) 2003 Elsevier Science Ltd. All rights reserved."
DOI: 10.1016/S0967-0645(03)00075-4
Subject turbidity currents
transantarctic mountains
water production
rockall trough
north-atlantic
weddell sea
waves
margin
circulation
deposition


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