Morphology and evolution of a modern mixed (turbidite-contourite) depositional system associated with deeply-incised submarine canyons in the Patagonian Continental Margin

Abstract

This study integrates a novel multi-beam bathymetry and high-resolution sub-bottom seismic database with previous works, to investigate a Late Quaternary Mixed (turbidite-contourite) Depositional System (MDS) related to a major submarine canyon system located on the Patagonian Continental Margin (PCM) between water depths of 1500 and 4000 m. The studied MDS exhibits unique and unusual features, including the along-slope deviation of three submarine canyons, large-mounded drifts (>100 ms TWT) forming downstream of canyons, and small patchy drifts (a few tens ms TWT) accumulating in canyon-free slope areas. The genesis of these features is explained by a temporal substitution from contourite to mixed settings and different styles of interaction between along-slope and across- slope processes. The along-slope deviation of the canyons is associated with the temporal substitution of contourite processes dominated period to the establishment of a MDS, marked by increased down-slope activity inferred to have occurred after the Mid-Pleistocene Transition (MPT). The fossil mounded morphologies developed during the dominant contourite period (pre MPT) acted as barriers to the subsequent submarine canyons formed during the increased down-slope activity period (post MPT), causing them to deviate by 90◦ along the slope. After the MPT, spatial intercalation and interactions between along and across slope processes produced patchy and mounded drifts. The patchy drifts are associated with unconfined settings and are interpreted as the outcome of turbidites redistributed by bottom currents. Synchronous interactions between along-slope and across-slope processes appear to have played a crucial role in the formation of large, mounded drifts near sub- marine canyons. This study highlights the temporal and spatial complexity of MDSs and provides new insights into their development within submarine canyon systems. Additionally, this work addresses the role that the stratification of deep-water masses could have played in the distribution of sediments along the PCM during the Late Quaternary.