The Powell basin oceanic spreading and sedimentary filling during Scotia Arc development (Antarctica)

Group GSI.IR
Location International Geological Congress,oslo 2008
Author Rodriguez Fernandez, Jose۱; Galindo-Zaldivar, Jesus۲; Schreider, Anatoly۳; Suriٌach, Emma۴; Bohoyo, Fernando۵; Maldonado, Andres۱
Holding Date 03 September 2008

The Powell Basin is a small restricted ocean basin located at the NE end of the Antarctic Peninsula. Its geometry is a result of the asymmetric opening produced by the drifting towards the E of the South Orkney Microcontinent. This fragmentation process was part of the Scotia Arc development that formed since the Oligocene.
The oceanic crust of Powell Basin is bounded by NE and SW passive continental margins, and NW and S transcurrent and transtensional margins. The NE margin, steep and starved, and the SW with smooth bathymetry and a greater sediment accumulation, evidence the asymmetric architecture of the basin and its sedimentary infill. The basin is only open to deep oceanic circulation in the SE, where basin connects with the Weddell Sea and Jane Basin, and no prominent relief is recognized. The topography of the basin shows a central region between the basin plain and the footslope depressed by 2-3 km relative to the adjacent margins. This region is divided into two sub-basins to the E and W of a marked central arcuate old spreading centre of NW-SE average trend.
Magnetic anomalies obtained in a marine cross section of Powell Basin shows two fitting possibilities. The youngest one suggests a spreading period between 6B and 5D anomalies (Early Miocene). However a good model, that takes into account the possibility of an overlapping spreading centre, points that oceanic spreading may occurred in between anomalies 12 and 7A (Oligocene).
Two main sedimentary sequences are identified in the sedimentary infill of the basin. The lowest sequence is located from the distal continental margin and basin plain to the NW-SE oriented axis, where they onlap the flanks of the extinct mid-oceanic ridge. The upper one covers the entire basin and the oceanic spreading centre. It is two or three times thicker than the lower unit. Its geometry is a broad downward convex lens with an irregular bottom; the top is the flat basin floor and display an expansive geometry onlapping the footslope of continental margins. The basin filling was controlled by the interaction of the tectonic processes that opened the basin, the deep oceanic flows that transport most of the accumulated sediments, and the sedimentary dynamics of the surrounding continental margins.
To determine the variation of the sedimentation rates over time, the sedimentary record was decompacted during backstripping analyses. The Powell Basin has acted like a trap for sediments coming mainly from outside of the basin. During some periods strong and deep anticlockwise currents associated with the Weddell Gyre generated large contouritc sediment in its northern half. The remarkable thickness of accumulated sediments over the last sequence has been also favoured by the glacier dynamics of the region.