EVIDENCE OF LANDUSE AND CLIMATE CHANGE FROM EL CHARQUITO, OAXACA, MEXICO

Archaeological and paleoecological research in the Río Verde Valley, Oaxaca, has developed a detailed and complex understanding of human land interactions over the past 4000 yr. Settlement in the valley appears to be associated with dynamic changes in the Río Verde, which underwent a morphological shift from a deep meandering channel to a broad, shallow braided form by ~3200 cal B.P. and the associated development of a broad rich floodplain. While archaeological settlement data from the valley can be traced to the Early Formative (4120-2755 cal B.P.) significant population increases occurred and culminated in the Terminal Formative (2065-1620 cal B.P.) with the development of an urban center at Río Viejo (RV), located on the western side of the river. During the Early Classic (1620-1330 cal B.P.) RV declined in size from 200 to 75 ha as occupation switched to the western piedmont. RV saw a renaissance during the Late Classic (1330-1060 cal B.P.) growing to 250 ha but declined again and was abandoned during the Postclassic (1150-428 cal B.P.) when occupation refocused across the river into the eastern piedmont.

Paleoecological reconstructions throughout the western floodplain and southern coastal region have determined shifts in land use generally paralleling settlement data patterns. In this paper we present a ~2500 yr reconstruction from a freshwater lake, El Charquito (0.2 km²), which is situated approximately 10 km north of RV. Carbon isotope, maize pollen, and macroscopic charcoal records indicate episodic agricultural activity ~2300, 1800, 1400, 1200 and 950 cal B.P. This agricultural activity is typically associated with high magnetic susceptibility levels suggesting erosional inputs. Significantly, macroscopic charcoal concentrations drop to negligible amounts between 740-500 cal B.P. indicating a cessation of burning. Burning did not resume until the latter end of the Colonial period. Elevated carbonate levels (inferred lake drawdowns) occurred at ~ 1700, 1000, 900 cal B.P. and from 750- 500 cal B.P., indicating multi-decadal droughts which culminated in centennial long drought coincident with the Late Postclassic. This is the first evidence for climatic changes in the valley. The data will facilitate a more complete model of the history of human-environment interactions throughout the valley.