LAUSR

Abstract The reconstruction of glacial paleolake formation and evolution allows the understanding of glacier advance and retreat behavior for longer periods of time. New datings obtained from paleolacustrine deposits in the Argentinian Patagonian Andes (Northwestern region of Santa Cruz Province) reveal that glacial lakes formed before the Last Glacial Maximum, they being as old as 31,278 cal yr BP, and evolved until 6900 cal yr BP. The interpretation of stratigraphic profiles described in different sectors of the Perito Moreno National Park (PMNP) allows reconstructing lacustrine, glaciolacustrine, glacial till and delta paleoenvironments. In each sector, organic-rich sediments were also sampled to obtain four absolute ages through AMS methodology. Thus, the paleogeographic reconstructions proposed are based on paleobathymetries performed from digital elevation models, datings and facies distribution of lacustrine deposits (mainly composed of laminated silts with subordinated sands and muds). Based on these new data, the paleogeography of this area is characterized by two lakes at 880 m.a.s.l at 31,200 ca yr BP, one directly related to modern Belgrano lake, while the other is probably related to the Burmeister lake but more than 10 km toward the East as respect to its current position. The paleogeography reconstruction shows, between 11,731 cal yr BP and 10,819 cal yr BP, the existence of a major paleolake at 900–920 m.a.s.l. which was connected to several modern lakes. Finally, a decrease of the paleolake level between 900 and 890 m.a.s.l. was recorded at 6900 cal yr BP which produced two major lacustrine systems separated by moraine deposits.