Palaeoenvironmental evidence for the Late Wisconsin/Holocene transition in the Strait of Magellan, southern Patagonia
A palaeoenvironmental record for the Wisconsin Later Glacial is provided from ten sites in the Magellan Region, southern Chile. Palynological and lithostratigraphical evidence provided by the sites was correlated with other palaeoenvironmental data from the Magellan region using 14C dating and tephrochronology. This enabled the construction of a regional record of environmental change that was compared with records in northern Patagonia and the Southern Hemisphere. Deglaciation of the Strait of Magellan began sometime before 16,590 yrs BP. A large Late Glacial ice advance believed to have occurred in the Strait of Magellan and contemporary with ice advances in northern Patagonia (c. 15,000-14,000 yrs BP) is not compatible with the 14C dating evidence. However, a Late Glacial ice advance along the Strait of Magellan was indicated by the glaciotectonic deformation of, and deposition of glaciolacustrine sediments above the Volcan Reclus tephra layer. Eight 14C dates provided the mean age estimate of 12,010±55 yrs BP for the deposition of the tephra. The erosion of a raised beach into the glaciolacustrine sediments after 7,950±60yrs BP provided the minimum age for the ice advance. Palynological evidence suggested that cold climatic conditions prevailed throughout the Wisconsin Late Glacial. The dominance of eurythermic pollen taxa, components of Patagonian steppe and glacial tundra vegetation, makes it difficult to infer a detailed climatic signal for the Wisconsin Late Glacial. However, a probable climatic deterioration occurred between c. 15,850-14,900 yrs BP. This may have been contemporary with an ice advance in northern Patagonia. A controversial climatic cooling correlated to the Northern Hemisphere Younger Dryas was not evident in the pollen record. The expansion of Nothofagus forest at c. 10,000 yrs BP indicated a change to a warmer environment contemporary with an intense arid phase. Therefore, it is likely that the large Late Glacial ice advance in the Strait of Magellan occurred between c. 12,000-10,000 yrs BP.