Geomorphological Expression of the Last Glacial Maximum (LGM) in Lago Argentino, Southern Patagonian Icefield

Geomorphological mapping is a widely used technique for examining the Earth surface processes responsible for landscape evolution. Moreover, it provides the essential geomorphological framework for establishing glacial chronologies, and therefore also, for paleoclimatic reconstructions. Located to the east of the Southern Patagonian Icefield (SPI), Lago Argentino and the upper Santa Cruz River valley contain well-preserved landforms and deposits critical to understanding past ice sheet behavior during multiple prior glaciations. Darwin (1842) observed large erratic boulders on the upper Santa Cruz River valley, indicative of past glacial activity, and Caldenius (1932) produced the first geomorphological map. Later, Strelin (1995) and Strelin and Malagnino (1996) described deposits associated with up to five Pleistocene glaciations. They proposed that a former `Argentino Glacier' extended eastward from Lago Argentino and that multiple past proglacial lakes existed in the upper Santa Cruz River valley.

Even though recent studies focused on the dynamics of the Patagonian Ice Sheet from 35 ka to present (Davies et al., 2020), little information is available from this region about the chronology of late Pleistocene glaciations, including the LGM. In an effort to reduce uncertainties in the extent and behavior of the Patagonian Ice Sheet during this period in the Lago Argentino region, we conducted two field seasons (2019 and 2020) in the upper Santa Cruz River valley. We surveyed glacial landforms and exposed sediments and then selected and sampled large boulders on moraine crests to obtain cosmogenic radionuclide (CRN) exposure ages of glacial deposits. Furthermore, we surveyed and sampled fluvial terraces of the Santa Cruz River valley to perform Optically Stimulated Luminescence (OSL) dating in order to gain insight into the glaciofluvial evolution of the landscape during the last glacial/interglacial transition. This mapping helps to determine analysis priorities for samples already collected and to identify key sites for future sampling. Moreover, through the use of remotely sensed data, such as satellite imagery and a high-resolution DEM, and by compiling previous work, we are producing a refined geomorphological map to improve the reconstruction of the glacial history in the region.