Holocene glacial variations in Central Patagonia, Aisen, Chile: geomorphological evidences.

Abstract

During the Holocene, the patagonian glaciers were characterized by geomorphologically registered advances and retreats. This paper presents the geomorphological evolution and evidences of Holocene glacial advances within a segment in Central Patagonia Cordillera. This area will be used as a reference for studying the postglacial paleoclimatic evolution in the southernmost part of South America. The study area is the Rio Blanco basin (45º30’S), located in Central Patagonia (Aisen Region, Chile). Radiometric dating of organic sediments, within terminal moraines, provides preliminary data of two glacial advances. The first one is represented by the Lake Elizalde frontal moraine, which yielded a 14C age of 9.370±50 years BP (10,700 to 10,480 cal. yr BP). According to this chronological age, this glacial event took place in the Early Holocene. This glacial advance, being 100 to 200 years older than that observed immediately south of the study area, on the eastern edge of General Carrera Lake (or Buenos Aires Lake, in Argentina) and approximately 100 years younger than the event recorded in the Puerto Banderas I moraine (Argentino Lake, 50ºS). These results show that the behavior patterns of the Central Patagonia glaciers differ from that observed both in the Lake District (41ºS, Chile) and in the Magallanes District (54°S, Chile), where there are no traces of glacial readvancement recorded during the Early Holocene. After a major retreat to the west, a more recent glacial advance occurred in the Quetro river valley (a tributary river of the Blanco river), at an age prior to 2.250±40 BP (2.340 to 2.150 cal. yr BP), comparable to the cold stage of the Middle Neoglacial, interpreted to have occurred in different parts of Patagonia. Confronting these results with previously published pollen records, we postulate that the cause of both glacier fluctuations is regional variations in the atmospheric temperature and precipitations.