Internal structure of a contourite drift generated by the Antarctic Circumpolar Current

Koenitz, D. and White, N. J. and McCave, I. N. and Hobbs, R. W. (2008) Internal structure of a contourite drift generated by the Antarctic Circumpolar Current. G3 Geochemistry Geophysics Geosystems, 9 (6). Q06012. ISSN 1525-2027 DOI

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We describe the internal structure and stratigraphy of a well-imaged contourite drift from the Southern Ocean. This drift, which we have named the South Falkland Slope Drift, lies on the northern flank of the Falkland Trough due south of the Falkland Islands. Drifts which occur directly in the path of the Antarctic Circumpolar Current (ACC), downstream of the Drake Passage gateway, are of considerable paleoceanographic significance since their detailed stratigraphic record will help to constrain the history of the ACC. We have reprocessed a grid of seismic reflection profiles generously provided by WesternGeco Ltd. in order to enhance imaging of the South Falkland Slope Drift and of drift deposits within the trough. The resultant high-quality images enable us to map the internal architecture of these drifts in unprecedented detail. By combining seismic stratigraphic mapping with measured sedimentation rates from nearby boreholes, we have inferred ages of the principal mappable horizons. With minor adjustments to sedimentation rates through time, we can show that these ages correspond to significant Southern Ocean events. We propose that the South Falkland Slope Drift initiated at 24.5–20.5 Ma, in accordance with some, but not all, published estimates of ACC establishment. A highly reflective horizon with an estimated age of 14.5 Ma corresponds to growth of the East Antarctic Ice Sheet, which led to a period of significant global cooling. A similarly bright reflective horizon with an estimated age of 9 Ma is thought to be related to a reorganization of bottom current flow which just predated establishment of grounded ice sheets on the Antarctic Peninsular shelf. Finally, a prominent early Pliocene unconformity at 4.5 Ma may be linked with the onset of major Northern Hemisphere glaciation or with Antarctic ice sheet expansion. We conclude that this well-imaged drift is an important, and largely continuous, stratigraphic record of ACC activity and suggest that it would be an excellent drilling target.

Item Type: Article
Uncontrolled Keywords: 08AREP IA55
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: G3 Geochemistry Geophysics Geosystems
Volume: 9
Page Range: Q06012
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:02
Last Modified: 23 Jul 2013 10:07

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