Late Neogene intensification of deep ocean circulation: evidence from seismic profiling of a mixed turbidite - contourite system at the Argentine Margin

• Main Authors: Gruetzner, Jens, Uenzelmann-Neben, Gabriele, Franke, Dieter
• Format: Conference Object
• Language: unknown
• Published: 2013
• Subjects: Antarctic; Argentine; Antarc*
• Online Access: https://epic.awi.de/id/eprint/33334/; https://hdl.handle.net/10013/epic.41795

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 and sediment drifts. 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 a slope plastered drift occurs in ~3000 m water depth seaward of the 3000 m isobath. The drift has a thickness of ~400 - 600 m and a width of ~10 - 20 km and can be traced for ~100 km within the working area. The feature likely is a northward extension of a current derived unit identified in the terraces sector and indicates that during the Plio-Pleistocene strong current controlled sedimentation occurred close to the interface between Lower Circumpolar Deep Water (LCDW) 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 ...