HOLOCENE VARIATIONS OF AMEGHINO GLACIER, SOUTHERN PATAGONIA

This study reports new data concerning the Holocene glaciation of Ameg hino Glacier, an eastern outlet of the Southern Patagonia Icefield. Th e lowest 7 km of the valley occupied by Ameghino Glacier is now ice-fr ee, of which the upper 3.7 km is a moraine-dammed proglacial lake. Man y glacial features are present in the Ameghino Valley. Across the vall ey floor, four terminal moraines have been identified, each representi ng a Neoglacial advance. Prominent vegetation trimlines are associated with the youngest of these moraines (M IV) which dammed the proglacia l lake. Samples for C-14 dating collected at the trimlines and from th e valley floors indicate that the formation of M IV, the culmination o f the recent maximum glaciation, occurred c. AD 1600-1700, and that de position of the valley train occurred c. AD 1500. Large standing trees which were buried and killed by this period of deposition have subseq uently been exhumed by river erosion. The glacier may have remained at the trimline level until around AD 1870-1880, the date obtained by Ni chols and Miller (1951) from dendrochronological analyses. The number of Neoglacial advances (4) identified in the Ameghino Valley is the sa me as that recently identified at two other Patagonian glaciers, Upsal a and Tyndall, and the date of the latest glacial episode, the 'Little Ice Age', is found to be synchronous. However, the ages of the earlie r three Neoglacial episodes remain unknown.