PALYNOLOGY OF CHIGNAHUAPAN LAKE, CENTRAL MEXICO

A palynological análisis of sediments from Lake Chignahuapan, allowed the reconstruction of vegetation and climate. Six sediment cores were obtained. The samples were treated with acids, acetolised. The data were analysed with TILIA and CONISS.

Early Holocene, Zone I, 9800-8500 BP

Conspicious oscillations are registered of the Pine forest and the moist forest, with Alnus as an important element. The oak forest remains constant. These changes correspond changes from a humid temperate climate to a temperate subhumid climate, supported by the presence of Abies.

Lower mid Holocene, zone II 8500–5200 BP

Pine forest is dominating, the moist forest disappears but increments at the end of the pollen zone, the oak forest seems to disappear. This period could be by erosion as it is indicated by the presence of sands. This zone corresponds to a temperate climate, without fluctuations.

Upper mid Holocene, zone III, 5200-3,500 BP

This zone is characterized by an increase of the oak forest with a maximum representation. The moist forest shows fluctuations. The pine forest shows low values with oscillations, decline of the oak and moist forest is registered.

Late Holocene, Zone IV, 3500–1300 BP

This zone is characterized by a slight increase of the pine forest, and a decrease of the moist and oak forest, It corresponds to a temperate climate, slightly colder than the preceding zone. Presence of man is indicated by the increase of Cheno-Ams, Asteraceae, Poaceae and the appearance of Cucurbitaceae and Zea mays.

Recent, 1300 till present

This zone is characterized by a continuos increase of grassland, and the pine forest, while the oak forest decreases. Climatic conditions are very similar to actual ones.

Conclusions

Five zones were recognized which show climatic and vegetational fluctuations of the last 10 000 years. Fluctuations are mainly changes in available humidity. Presence of Zea mays, Cucurbitaceae and Cheno. Ams during the last 3000 years is related with agricultural practices. The result confirm other data for the Central Mexican region.