Holocene environmental change in the Zacapu Basin, Mexico: a diatom-based record

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Abstract
The Zacapu basin, Michoacán, Mexico, is one of a series of internally drained lake basins in the central highlands of Mexico. The basin has a history of occupation spanning at least 2000 years and before the arrival of the Spanish was a major centre for the Purépecha culture. Results are presented of diatom studies from four lacustrine sediment sequences which have Holocene radiocarbon dates: CEMCA Point 1, CEMCA Point 4, the Zacapu core and Zacapu Section 1. These lie along a transect from the former marsh floor up to the western slopes of the basin. Zacapu Section 1 indicates a deep lake in the basin at some time, but the date on this section is thought to be unreliable and the sediments are probably Pleistocene in age. The other sequences record few major changes in water level in the basin, although dry episodes occurred about 4500 BP and, more severely, about 1000 BP. A period of marked catchment disturbance about 7000 to 6000 BP is believed to be the result of volcanic activity on the western flank of the basin. Major anthropogenic disturbance is recorded over the Postclassic and Hispanic periods (since about AD 900).