Depositional patterns observed at Drift 7, Antarctic Peninsula

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The continental rise west of the Antarctic Peninsula is characterized by 12 asymmetric sediment mounds, which elevate up to 1000 m above the surrounding sea floor and are interpreted as drifts (Rebesco et al. 2002). The drifts are separated by erosional channels starting at the base of the continental slope and running seaward down to the abyssal plains. Investigation of high-resolution multichannel reflection seismic profiles carried out at Drift 7 enabled the identification of six seismostratigraphic units representing a pre-drift (sedimentary units M6 and M5), drift growth (sedimentary units M4 and M3), and drift maintenance (sedimentary units M2 and M1) stage (Rebesco et al. 1997, 2003). Boundaries between the defined seismostratigraphic units were tracked along previously interpreted and not-interpreted seismic lines crossing Drift 7 within an interpretation system database (LANDMARKTM). Post-cruise work on sedimentary sequences recovered at ODP Leg 178 Site 1095, which is located at the distal flank of Drift 7, and Site 1096, which lies near its crest, allowed the conversion of the acoustic depths of the boundaries between the seismostratigraphic units into vertical subbottom depths as well as the assignment of these boundaries to chronostratigraphic ages (Volpi et al. 2001,Barker et al. 2002).The analysis of the different sedimentary unitss distribution reveals the following depositional pattern: Whereas units M6 (>25 Ma) and M5 (15-25 Ma) still rest close to the continental slope, we see a huge build-out for unit M4 (9.5-15 Ma). After that a retreat in the location of the depocentre back towards the continental slope can be detected. A channel between Drift 7 and the continental slope cannot be observed at any stage. Towards Drift 6, we observe channel development starting at the M5/M6 boundary (25 Ma).Those observations indicate modification in sediment supply and transport. Before 15 Ma a SW-setting, near bottom contour current deflected the moderate sediment input towards the southwest, where the material was deposited on and on the lee-side of a basement ridge. Sediment supply strongly increased between 15 and 9.5 Ma indicating turbidity currents, which were much stronger than the bottom current. We regard this as indications for a major advance of the Antarctic ice shelf. Since 9.5 Ma turbidity currents appear to have diminished with the bottom current again taking up the more important role.

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Conference (Talk)
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XXVIII SCAR Open Science Meeting, 25-31 July, Bremen, germany..
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Uenzelmann-Neben, G. , Hillenbrand, C. D. and Rebesco, M. (2004): Depositional patterns observed at Drift 7, Antarctic Peninsula , XXVIII SCAR Open Science Meeting, 25-31 July, Bremen, germany. .

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