Quaternary paleoecology of Fuego-Patagonia

Abstract

The paleoecology of Quaternary events in Fuego-Patagonia derives from biogenic deposits emplaced before, during, and following the last glacial maximum. Paleoecological data center on the palynology of stratigraphic sections of (1) biogenic beds in a proglacial delta of finite and infinite age at Lago Fagnano, and of (2) selected sites of radiocarbondated, late-glacial and postglacial, mire/lacustrine deposits at Puerto Harberton, Lago Fagnano, and Bahía Inútil in Fuegia and at Punta Arenas and Torres del Paine in Patagonia. Events embrace noteworthy sequences involving vegetation and climate, atmospheric circulation, fire, human presence, land-sea level relations, and volcanism. Data from peaty horizons in the Pleistocene delta at Lago Fagnano, dated at about 40000 and >;58000 yr BP, indicate treeless steppe/tundra under a cold, dry, interstadial climate. Younger deposits, formed following the last glacial maximum dated at >; 16590 in the Estrecho de Magallanes and >;14640 yr BP in Canal Beagle, show climatically variable, late-glacial episodes of woodland - steppe/tundra interaction. In the warmer early Holocene, progressive development of closed forest replacing open woodland and steppe, is a general feature of the vegetation; evident after 5000 yr BP, under a cool-temperate, more humid climate, are the increased presence of closed forest and the spread of mires on the landscape. Apparent from the Holocene vegetation pattern is the greater frequency/intensity of cyclonic storms of the prevailing westerlies crossing Fuego-Patagonia after 5000 yr BP. Charcoal, in addition to fossil pollen in the records, is ascribed to Paleoindian burning, as purposely practiced during hunting to congregate game. On Isla Grande de Tierra del Fuego, where volcanic activity and lightning are not considered to be causal agents of fire, burning attributed to Paleoindian hunters is traceable from late-glacial charcoal remains as earlyas 13280 yr BP. Fires in Fuego-Patagonia, judged from the frequency of charcoal, wete commonplace in the early Holocene and later more occasional, possiby reflecting changes in size and routes of migration in human populations.