Late-glacial history of Lago Argentino, Argentina, and age of the Puerto Bandera moraines

In the west-central part of Lago Argentino, the Puerto Bandera moraines are clearly detached from longer, more prominent moraines of the last glaciati on and from shorter and smaller Neoglacial moraines, Scientists have long s peculated about the age of the Puerto Bandera moraines, Detailed geomorphol ogic studies in the western area of Lago Argentino, including stratigraphic profiles at Bahia del Quemado in the northern branch (Brazo Norte), indica te that the Puerto Bandera moraines were deposited by three pulses of ice. Each of the three pulses is represented by single moraine ridges and belts of tightly arranged ridges. The timing of the three glacier advances was es tablished by radiocarbon dating, including data published by John Mercer. T he oldest moraine system, formed during the Puerto Bandera I substade, was deposited ca. 13,000 C-14 yr B.P. Moraines of the Puerto Bandera II substad e were deposited ca, 11,000 C-14 yr B.P. The youngest moraine system was de posited during a minor readvance, shortly before 10,390 C-14 yr B.P., and t hus appears to have occurred some time during the European Younger Dryas in terval. After this third substade, the ice tongues retreated into the inter ior branches of Lago Argentino and have remained there since. Evidence foun d at Bahia del Quemado, together with data provided by other authors, attes ts to a significant climatic change by the middle Holocene, which we believ e occurred during the Herminita advance, the first Holocene glacial readvan ce recognized within the area. (C) 2000 University of Washington.