Lacustrine sediments provide one of the best continental archives to reconstruct environmental processes. Located at ~54°S in the Island of Tierra del Fuego, Lago Fagnano is the biggest (~110 km long), southernmost non-ice covered lake in the world outside Antarctica. The lake occupies two basins forming part of a chain of tectonic depressions along the Magallanes-Fagnano transform system (MFT). In addition to its tectonic origin, the lake evolved under the reach and influence of past Andean glaciations. Therefore, its sediments contain a unique record of past tectonic and climatic events.

A multi-proxy approach combining seismic reflection profiling and detailed analyses of long sedimentary cores retrieved from Lago Fagnano allowed addressing questions regarding past regional environmental changes. More than 800 km of geophysical survey, combining simultaneously high-resolution 3.5 kHz (pinger) single-channel and 1 in³ airgun multi-channel systems, allowed visualizing both the most recent lacustrine sediments and the oldest deposits, respectively. The concepts of seismic sequence stratigraphy were applied to the sedimentary infill to reconstruct past environmental conditions. The combination of geophysical data from the lacustrine basin with geomorphological studies allowed assigning a sequence of subaquatic moraines within Lago Fagnano seismic stratigraphy. During the Last Glacial Maxima, the Fagnano glacier occupied the lake basin spreading through three different lobes and reaching a maximum length of ~130 km. A set of submerged frontal moraines covered by lacustrine infilling identified in the seismic survey suggests occasional eastward re-advances of the paleo-glacier within the overall westward deglaciation pattern. Radiocarbon dating permitted estimation of sedimentation rate providing an indirect age for one of these intervals of glacier re-advance. This major glacier advance seems to be synchronous with the Antarctic Cold Reversal (ACR) and was probably more severe in magnitude in this region than the Northern Hemisphere Younger Dryas Chronozone (YDC).

Seismic profiling was complemented with sedimentary cores obtained at the deep basin assisting in the calibration of the seismic signal and permitting a core-to-seismic correlation. This exercise improved the understanding of the seismic architecture of the basin infill. Several piston and gravity cores were retrieved in the deeper parts of the lake generating composite sections for the eastern and western basins. The age model relies on a well-dated tephra layer and several AMS-¹⁴C samples obtained on wood and pollen remains. The Holocene sedimentary record was reconstructed through the multi-proxy study of selected cores. The sediments consist of laminated sequences occasionally interrupted by homogenous beds several tens of cm thick interpreted as megaturbidites. Detailed petrophysical, sedimentological and geochemical studies of the laminated intervals reveal fluctuations in major and trace elements as well as content of total organic matter and palynological data that display an apparent cyclicity. These results provide a unique dataset that is further compared with other regional marine and continental archives. This comparison allowed identifying known intervals of Late Holocene climate fluctuations and to constraint the timing of the onset of the Southern Westerlies in Tierra del Fuego. This exercise serves to validate the outcome of existing ocean and atmospheric climatic models for the Southern Hemisphere and as a first step for interhemispheric climate correlation.

The combined geophysical, sedimentological and geochemical record of Lago Fagnano revealed recurrent mass wasting events during the entire Holocene. The spatial and temporal distribution of twenty-two megaturbidite events was catalogued within the lake. Simultaneously-triggered basin-wide lateral slope failure and formation of megaturbidites are interpreted as fingerprints of paleo-seismicity along the MFT fault zone. The proposed age model revealed an 800-1000 years recurrence of slope failure and megaturbidite formation. These results provide unique data about the frequency and plausible magnitude of Holocene earthquakes in Tierra del Fuego. Hence, this first record of past slope failure in Lago Fagnano is a corner-stone for further studies related to geohazards in Tierra del Fuego.