Interaction of processes and importance of contourites: insights from the detailed morphology of sediment Drift 7, Antarctica

Abstract

As the definition of contourites has widened to embrace a large spectrum of sediments in so-called mixed systems, the distinction between contourites and turbidites has become at times vague. The case history of sediment Drift 7 off the Antarctic Peninsula is analysed in this paper in the light of newly acquired swath bathymetry data. The co-existence of various sedimentary processes is reflected in a complex morphology: erosional gullies produced by debris flows on the upper part of the continental slope; deeply incised channels at the slope base; main trunk-type inter-drift turbidity channels separating the drifts; slide scars; undulating depositional bedforms interpreted as bottom-current sediment waves; fluid escape structures perhaps associated with deep-water coral bioherms. The data suggest that Drift 7 is a genuine sediment drift in which bottom currents pirate the sediment of the turbidity currents. Finally, we propose that the control on location and elongation of the drift is inherited from an older margin structure. The relationships between bottom current and deposition are investigated through a comparison with the SE Greenland continental margin, an analogous counterpart in the northern hemisphere.

Paleocurrent directions from paleomagnetic reorientation of magnetic fabrics in deep-sea sediments at the Antarctic Peninsula Pacific margin (ODP Sites 1095, 1101)

“…At Sites 1095 and 1101, this approach produces a generally NW-SE trending paleoflow direction for the Miocene through the Pleistocene. At Site 1095, Drift 7, this azimuth direction matches the elongation of the sediment wave described by Rebesco et al (2007), who similarly interpret the sediments as deposited by contour currents rather than by turbidity currents. We similarly interpret the results at Site 1101, which also show a NW-SE trend, as indicative of deposition from contourites.…”

“…A recent study by Rebesco et al (2007) allows us to compare the paleocurrent directions at Site 1095 with the morphology of the ocean floor. According to these authors, sediment at Drift 7 is interpreted as the product of weak flowing bottom currents pirating the suspended fine material from turbidity currents.…”

“…According to these authors, sediment at Drift 7 is interpreted as the product of weak flowing bottom currents pirating the suspended fine material from turbidity currents. The NE side of Drift 7 is characterized by an undulating depositional bedform as revealed by seismic profiles, interpreted as a sediment wave field (Camerlenghi et al, 1997a,b;Rebesco et al, 2007). Just north of Site 1095, the Alexander Channel extends for some 100 km with a NW-SE orientation.…”

Arctic and Antarctic submarine gullies—A comparison of high latitude continental margins

“…One key difference is the greater prevalence of thin hemipelagic/contouritic sediments on parts of the Arctic continental slope, which form weak interglacial layers interbedded between the glacigenic sediments Vorren, 1995, 2000;Laberg and Camerlenghi, 2008). Although large mounds, interpreted as sediment drifts produced by bottom currents, occur on some areas of the Antarctic continental rise (Rebesco et al, 1996(Rebesco et al, , 2007Weber et al, 2011), little evidence exists for weak geological layers on the Antarctic upper slope .…”

Glacial contourites on the Antarctic Peninsula margin: insight for palaeoenvironmental and palaeoclimatic conditions

“…Sediments across the continental shelf were transported mainly by ice-streams and delivered to the continental slope and rise during the periods of maximum glacial expansion. The continental rise hosts a number of large sediment drifts separated by dendritic deep-sea channel systems that originated on the lower continental slope in alignment with the reaches of each glacial trough (Amblas et al 2006;Rebesco et al 2007).…”