Sediment deposition and erosion at the Argentine continental slope: evidence for an intensification of deep ocean circulation during the Late Neogene


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Jens.Gruetzner [ at ] awi.de

Abstract

A complex history of sediment deposition at the Argentine continental margin during the Plio-Pleistocene is indicated by the presence of a canyon system, submarine channels, sediment drifts and sediment waves. We use a dense grid of seismic reflection profiles together with bathymetric data to identify sedimentary units, map depocenter geometries, separate along-slope from down-slope processes and relate depositional stages to past changes in climate, oceanography and tectonics. The topmost seismic unit in the working area (40 to 48°S) exhibits a variety of co-occurring seismic and morphological features that are diagnostic for both down-slope and along-slope sediment redistribution. In general, current controlled sedimentation is more obvious south of 45°S (“terraces sector”) while in the northern part (“canyons sector”) of the working area contouritic features are reshaped by cross-slope erosion through canyons. Within the canyons sector an extensive field of migrating sediment waves is observed at a water depth of 2500 to 3500 m. The waves are 1.5 to 4 km wide and 30 to 100 m high. Buried waves overlying reflector AR7 (~6 Ma) indicate that the field has been active since the Early Pliocene. Seaward of the 3500 m isobaths a slope plastered drift with a thickness of ~400 - 600 m and a width of ~10 - 20 km and can be traced for ~100 km within the working area. These features likely are northward extensions of a current derived unit identified in the terraces sector and indicate that during the Plio-Pleistocene strong current controlled sedimentation occurred close to the interface between Circumpolar Deep Water (CDW) and Antarctic Bottom Water (AABW). Erosion via slope cutting canyons is most extensive in ~3000 m water depth at the central Argentine margin (43.5°S, 57.5°W) where multiple branches of the Ameghino canyon system join. None of the canyons in the working area cut into reflectors AR5/AR6 (~14 – 17 Ma), and only the main branches of the Ameghino canyon cut into reflector AR7 (~6 Ma) on the upper slope. Together with the fact that no buried canyons are observed this suggests that canyon development most likely occurred during the late Neogene possibly due to the buildup of slope instabilities caused by vigorous bottom current circulation. Such intensification during the Pliocene is evident in the terraces sector and may be related to stronger production of North Atlantic Deep Water (NADW) commencing around 6 Ma as well as an enhanced flow of NADW into the South Atlantic following the restriction of the Panamanian Isthmus at ~5 Ma.



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Conference (Talk)
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Primary Division
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Not peer-reviewed
Publication Status
Published
Event Details
30th IAS Meeting of Sedimentology, 02 Sep 2013 - 05 Sep 2013, Manchester, UK.
Eprint ID
33908
Cite as
Gruetzner, J. , Uenzelmann-Neben, G. and Franke, D. (2013): Sediment deposition and erosion at the Argentine continental slope: evidence for an intensification of deep ocean circulation during the Late Neogene , 30th IAS Meeting of Sedimentology, Manchester, UK, 2 September 2013 - 5 September 2013 .


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