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

Mixed (turbidite-contourite) depositional systems are formed by a complex interplay of deep-water processes. Anevaluation of their morphological elements and their lateral and spatial distribution is crucial to better understandthe interplay of transport and depositional processes, involving along-slope bottom currents and downslopeturbidity currents. This work investigates extensive and still active mixed depositional systems developedalong 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 investigatediverse morphological elements at a high-resolution spatial scale (10–100 m), using multibeam bathymetry andacoustic sub-bottom profiles. Four main seismic units define distinct evolutionary stages for the Pleistocene topresent day record: a) 1.3–1 Ma, characterized by aggradational mounded drifts built by a dominant along-slopebottom current; b) 1–0.6 Ma, built by synchronous interactions between a SW-flowing bottom current and NWdirectedturbidity currents; c) 0.6–0.2 Ma, characterized by deposition of thick gravitational deposits across themargin 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 speedfluctuations, and ephemeral turbidity currents led to intercalations of turbidites, contourites, reworked turbiditedeposits and hemipelagites. Alternations in the stratigraphic stacking pattern suggest cyclic spatial and temporalvariations of gravity-driven down-slope processes and along-slope bottom currents, which were responsible forthe construction of these modern mixed depositional systems and which themselves were controlled by glacialinterglacialchanges. The new results are compared with similar mixed depositional systems to decode the mainprocesses involved in their formation, explore their interactions at short- and long-term time scales, and proposea conceptual sedimentary model.