Sedimentary Model for Mixed Depositional Systems: Conceptual Implications

Along- and down-slope processes are fairly common processes along continental margins. The aforementioned processes and their interaction can build large mixed / hybrid (turbiditic-contouritic) depositional systems. These systems are characterized by a variability and complexity of features. Globally, several mixed systems have been identified on the Cenozoic, however their representation in the Mesozoic remains severely understated. This issue is aggravated if we consider that the diagnostic criteria for mixed systems is not fully defined and, therefore, not used to improve the examples already described in the literature. This work aims to contribute to a better understanding of the dynamics between along- and down-slope processes, by identifying significant modifications in physiographic features and stacking architectures, and by discriminating the mechanisms responsible for the formation of each feature and how they operate through time. To approach these objectives, we are studying two key areas: 1) a modern example on the Pacific Margin of the Antarctic Peninsula, characterized by a remarkable depositional system with several contourite mounded drifts and turbidite channels in the continental lower slope and continental rise; and 2) the Cretaceous record on the Argentine Margin, which comprises an extensive mixed system on the continental slope. This study is based on a compilation of swath multibeam bathymetry, high- and low-resolution seismic reflection datasets, well borehole data and sediment cores. The two examples share similar downslope elongated mounds along the lower slope and rise with asymmetric morphologies, marked by a smooth, aggradational side and a steep, eroded side with signs of mass movements. However, while the Antarctic Peninsula has a dendritic network of gullies and channels on the upper continental slope that converge into single turbidite channels on the lower slope and rise, the Argentine Margin is characterized by individual large channels that start at the continental shelf / upper slope and cut through the topography. The interpretation and integration of these results aims to propose a conceptual model for depositional mixed systems that will clarify the role and influence of bottom currents versus turbidity currents.