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.
Highlights
El sur de Chile tiene condiciones excepcionales para estudios paleoclimáticos debido a su emplazamiento en la vertiente barlovento de los Andes, bajo la influencia de los vientos húmedos del Oeste
This paper presents the geomorphological evolution and evidences of Holocene glacial advances within a segment in Central Patagonia Cordillera
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 and approximately 100 years younger than the event recorded in the Puerto Banderas I moraine (Argentino Lake, 50oS)
Summary
El sur de Chile tiene condiciones excepcionales para estudios paleoclimáticos debido a su emplazamiento en la vertiente barlovento de los Andes, bajo la influencia de los vientos húmedos del Oeste. Durante la Última Glaciación y hasta una edad aproximada de 14.600 años 14C Antes del Presente (AP), la Cordillera Andina estaba invadida por glaciares de circo, de valle y de piedemonte al norte de los 42oS, mientras que entre esta latitud y el extremo sur, extensos campos de hielo cubrían la mayor parte del relieve andino (Heusser, 2003; Laugenie, 1982) (Fig. 1). Con una fecha de inicio más tardía y un retroceso más temprano es el avance glaciar admitido en el frente del lago Argentino, en la vertiente oriental del Campo de Hielo Sur (Fig. 1); representado por la morrena interna de Puerto Banderas (50oS) la que ha sido datada de una edad superior a 10.390 e inferior a 11.170 años 14C AP (Strelin y Denton, 2005). Los resultados de la presente investigación proponen, a partir de evidencias geomorfológicas y dataciones 14C de materia orgánica contenida en sedimentos lacustres, la ocurrencia de al menos dos avances glaciares holocénicos en el margen oriental de la Cordillera Andina de Aisén (Patagonia Central): el primero habría ocurrido durante el Holoceno Temprano (10.000 a 8.000 14C AP) y el segundo, durante el Neoglacial
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