Mudwave activity and current-controlled sedimentation in Powell Basin, northern Weddell Sea, Antarctica

Abstract

An area of mudwave development has been identified from the northwestern Powell Basin, northern Weddell Sea, Antarctica. The wave-field is located near the base of the continental slope in water depths of 2800–3100 m, along the pathway of Antarctic Bottom Water (AABW) flow from the Weddell Sea. The waves are presently active, migrating up a low angle (0.6°) slope to the northwest. They are typically 20–50 m in amplitude and 2–4 km in wavelength, and cover an area greater than 1000 km 2. Swath mapping and high-resolution multi-channel seismic reflection profiling across the area show that the waves developed in association with basin floor channels and strongly current-influenced sediments. Acoustically, the sediments can be divided into three units. The uppermost unit, C, is 0.5 s twt (two-way time) thick with highly continuous, parallel reflectors displaying well-developed waveforms mimicking those at the seabed and, towards the southeast, a basin floor channel. Unit B is up to 0.8 s twt thick, with strong and continuous subhorizontal reflectors. In the mid-upper section of B are developed buried sinusoidal wave-forms and a base of slope depression or `moat' and a sediment drift which is infilled and buried, the reflector pattern suggesting sediment supply under current control alongslope, interpreted as contouritic sediments. A lower transparent unit, A, is 1–1.5 s twt thick, with occasional reflectors. The original construction of the waves may have been by turbidity currents predominantly supplied from the basin floor channels. Present-day deposition across the waves is maintained by fine-grained sediment as a result of the lateral transfer of distal turbidites from the basin floor channels by bottom currents. It is suggested that the initiation of current-influenced sedimentation was closely linked to the onset of AABW flow during the Early Miocene, following the separation of the South Orkney Microcontinent and the opening of the Powell Basin during the Late Oligocene.