Abstract
Located at 54ºS in the heart of the Island of Tierra del Fuego, Lago Fagnano occupies the deepest of a chain of en-echelon tectonic depressions along the Magallanes-Fagnano Transform system (MFT). A recent geophysical campaign combining 3.5 kHz (pinger) single-channel with 1 in3 airgun multi-channel systems surveyed more than 100 m of glacio-lacustrine sediments filling two main sub-basins. These data provide a unique opportunity to visualize the most recent lacustrine sequence with high-resolution while simultaneously imaging the oldest infill. A preliminary seismic stratigraphic analysis of the high-resolution 3.5 kHz pinger data allowed the identification of three major seismostratigraphic units (A, the oldest and C, the youngest). While unit A is interpreted as glacially derived sediments, the overlying unit B is interpreted as fining upward sequences of proglacial turbidites reflecting sediment pulses released by the retreating Fagnano glacier during the last deglaciation. A major environmental change occurred during deposition of unit C when pelagic style of sedimentation is intercalated by sequences of downslope mass flow events probably triggered by relatively strong tectonic pulses along the MFT system. Gravity cores show a regular alternation of light and dark laminae occasionally interrupted by homogenous sedimentary units interpreted as turbidites. Ultra-high resolution X-ray fluorescence micro-profiles show fluctuations in major trace elements at mm scale that may indicate seasonal variations in the sedimentary influx. These core data provide a unique record of decadal changes in regional climate that can be compared with other marine and continental archives to improve our understanding of the forcing mechanisms behind climate change.