HOLOCENE ENVIRONMENTAL-CHANGE IN THE ZACAPU BASIN, MEXICO - A DIATOM-BASED RECORD

The Zacapu basin, Michoacan, 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 ar rival of the Spanish was a major centre for the Purepecha culture. Res ults are presented of diatom studies from four lacustrine sediment seq uences which have Holocene radiocarbon dates: CEMCA Point 1, CEMCA Poi nt 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. Za capu Section 1 indicates a deep lake in the basin at some time, but th e date on this section is thought to be unreliable and the sediments a re probably Pleistocene in age. The other sequences record few major c hanges in water level in the basin, although dry episodes occurred abo ut 4500 BP and, more severely, about 1000 BP. A period of marked catch ment disturbance about 7000 to 6000 BP is believed to be the result of volcanic activity on the western flank of the basin. Major anthropoge nic disturbance is recorded over the Postclassic and Hispanic periods (since about AD 900).