Geophysical evidence of multiple glacier advances in Lago Fagnano (54°S), southernmost Patagonia

Abstract

The Island of Tierra del Fuego, at the southernmost extreme of Patagonia, is located in one of the most extensively glaciated areas of the Southern Hemisphere outside Antarctica during the late Pleistocene. The Lago Fagnano region, at ∼54°30′S and ∼68°W, has experienced several phases of glacier growth and retreat since the Last Glacial Maximum (LGM). We illustrate these phases using combined geomorphological, geophysical and coring surveys in Lago Fagnano itself, a ∼105 km-long, E–W-oriented glacio-tectonic basin. We identify and map a complex set of submerged frontal, central and lateral moraines covered by lacustrine sediments using seismic stratigraphic analysis of multi-channel profiles imaging the sub-lake floor. We then combine these geophysical data with field observations and regional maps of similar structures around the lake to reconstruct the spatial behavior of the Fagnano paleo-glacier since the LGM. We interpret the preserved frontal moraines as having formed during at least 20 re-advance stages of the glacier within a long-term deglaciation interval post-LGM. Preliminary tephrochronological dating of a ∼7.5 m long core indicates a step-wise deglaciation pattern comprising a final glacier re-advance stage at ∼11.2 ka BP.