Sedimentary model for mixed depositional systems along the Pacific margin of the Antarctic Peninsula: Decoding the interplay of deep-water processes

Abstract

Mixed (turbidite-contourite) depositional systems are formed by a complex interplay of deep-water processes. An evaluation of their morphological elements and their lateral and spatial distribution is crucial to better understand the interplay of transport and depositional processes, involving along-slope bottom currents and down-slope turbidity currents. This work investigates extensive and still active mixed depositional systems developed along the Pacific margin of the Antarctic Peninsula, which comprise large asymmetric mounded drifts, dendritic channel-complex systems and wide trunk channels. These systems offer a unique setting to investigate diverse morphological elements at a high-resolution spatial scale (10–100 m), using multibeam bathymetry and acoustic sub-bottom profiles. Four main seismic units define distinct evolutionary stages for the Pleistocene to present day record: a) 1.3–1 Ma, characterized by aggradational mounded drifts built by a dominant along-slope bottom current; b) 1–0.6 Ma, built by synchronous interactions between a SW-flowing bottom current and NW-directed turbidity currents; c) 0.6–0.2 Ma, characterized by deposition of thick gravitational deposits across the margin under a weak SW-flowing bottom current comprising modified Lower Circumpolar Deep Water (LCDW); and d) 0.2 Ma – present, when synchronous interactions between the bottom current, characterized by flow speed fluctuations, and ephemeral turbidity currents led to intercalations of turbidites, contourites, reworked turbidite deposits and hemipelagites. Alternations in the stratigraphic stacking pattern suggest cyclic spatial and temporal variations of gravity-driven down-slope processes and along-slope bottom currents, which were responsible for the construction of these modern mixed depositional systems and which themselves were controlled by glacial-interglacial changes. The new results are compared with similar mixed depositional systems to decode the main processes involved in their formation, explore their interactions at short- and long-term time scales, and propose a conceptual sedimentary model.