Resumo

CABALLERO, Margarita; LOZANO-GARCIA, Socorro; VAZQUEZ-SELEM, Lorenzo  e  ORTEGA, Beatriz. Evidence for climatic and environmental change in high central Mexico basins during the last glacial maximum. Bol. Soc. Geol. Mex [online]. 2010, vol.62, n.3, pp.359-377. ISSN 1405-3322.

Significant information is available regarding glacial history, lake level and vegetation history from several basins and volcanoes during the late Pleistocene in the Transmexican Volcanic Belt (TMVB). Here we present a synthesis and compilation of that information to establish the climatic conditions in this region during the Last Glacial Maximum. The data is organized in four time windows: Early Glacial: 25000-22000 cal BP, Last Glacial Maximum: 22000-18000 cal BP, Late Glacial: 18000-15000 cal BP and Terminal Glacial 15000-12000 cal BP. The late Pleistocene geomorphological evidence from Iztaccihuatl volcano offer the most complete record of glacial advances during the last 30000 yr; at other elevations the glacial history is fragmentary (due to volcanic activity) or more limited (due to lower altitudes). For the Early Glacial no evidence of glacial advance is recorded but data from the lacustrine basins indicate low lake levels. During the Last Glacial Maximum a decrease in temperature of 6 to 8° C is estimated, and the equilibrium line altitude is reconstructed at 3940 m for Iztaccíhuatl, 3400 m for Tancítaro,and 3650 m for Cofre de Perote. A downward displacement of ~ 1000 m for the limit of Pine forests with alpine vegetation, as well as changes in vegetation composition and distribution, are documented for the Late Glacial Maximum on the basis of palynological data. During this period low lake levels are recorded in the lakes of the Mexico and Lerma basins, while in the western sector of the TMVB most of the basins show low lake levels (Zirahuen, Zacapu and Cuitzeo) and only the record of Lake Patzcuaro suggests high stands for this period. Based on the synthesis of the data, a humidity gradient from the coasts towards the interior of the TMVB is inferred. For the Late Glacial period, a glacier retreat of ~100 m compared to the Last Glacial Maximum is detected at Iztaccíhuatl volcano. At the beginning of the Terminal Glacial all the glaciers retreated slowly and intermittently, then markedly after 14000 cal BP. At several lakes such as Tecocomulco, Texcoco, Cuitzeo and Zacapu sedimentation hiatus are recorded, indicating drier conditions.

Palavras-chave : Late Glacial; central Mexico; glacial history; paleolimnology; palynology; Transmexican Volcanic Belt.

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