Fossil pollen from Los Toldos locality: A record of the Late-glacial transition in the Extra-Andean Patagonia

Paleoenvironmental changes during the Late-glacial transition are interpret ed from a pollen record from two caves at Los Toldos (47 degrees 22' S; 68 degrees 58' W) in Extra-Andean Patagonia in Argentina. The paleoenvironment al interpretation is based on changes in the ratio between shrub and grass steppe taxa and on comparison with other pollen records from the region. Be tween 12,600 and 8750 yr BP two vegetational changes occurred thought to re flect the establishment of Holocene-type atmospheric circulation patterns. The first change is at ca. 11,000 yr BP expressed by replacement of shrub s teppe with Ephedra by a grass steppe. The second change occured ca. 10,000 yr BP when the grass steppe was replaced by a shrub steppe dominated by Ast eraceae. Before ca. 11,000 yr BP the environmental conditions were extremel y arid with precipitation lower than 200 mm. Between ca. 11,000 and ca. 10, 000 yr BP effective moisture increased, probably related to an increase in precipitation to about 200mm under cold conditions. A grass steppe extended through Patagonia and Tierra del Fuego, at least as far north as 47 degree s S. It is difficult to find modern analogues for pollen associations south of 47 degrees S older than 10,000 yr BP. Possibly at that time climate pat terns were markedly different from today. At about this time of environment al changes Level 11 industry associated with extinct grazing herbivores dev eloped. Starting at ca. 10,000 yr BP, with expansion of the shrub steppe of Asteraceae east of the Andes at 47 degrees to 52 degrees S and forest at 5 1 degrees-54 degrees S west of the Andes, temperature increased while water availability decreased. Precipitation probably was similar to the present, which suggests that the modern climate patterns were established at the be ginning of the Holocene. The Toldense Industry, which is associated with re mains of modern fauna as well as with the last remains of the Pleistocene f auna, developed in this period. The beginning of this development coincides with the extinction of Pleistocene fauna. (C) 1998 INQUA/Elsevier Science Ltd. All rights reserved.