T90 Topics in Geoarchaeology: Reconstructions of Ancient Landscapes and Paleoenvironments

Monday, 10 October 2011
8:00 AM - 12:00 PM
Room 101FG

PALEOENVIRONMENTAL RECONSTRUCTION AND OCCUPATION HISTORY AT THE U2 ARCHAEOLOGICAL FEATURE, RIO VIEJO, OAXACA

Paper number: T90-4
Program: Technical Sessions
Time: 8:35 AM – 8:50 AM

Authors

Abstract

Over 20 years of archaeological and geoarchaeological work in the lower Rio Verde Valley, Oaxaca, Mexico reveal a varied spatial relationship with the land in this dynamic floodplain region over the last 3 kyrs. Significant demographic expansion occurred by the Late Formative period following floodplain aggradation, alluviation, and a change in stream morphology. During the Classic and Postclassic periods, major shifts in settlement and land use occurred, primarily from the productive floodplain to the piedmont (which today has limited productivity). These changes appear to have occurred as a result of political developments. Previous paleoenvironmental reconstructions indicate periods of land use and abandonment by local farmers through time. These data provide limited spatial coverage for comparison with the archaeological record, thus precluding examination of human decision making involv­ing landuse, subsistence, and labor allocation which occur at much finer spatial and temporal scales.

To improve our spatial understanding of landuse trends we collected multiple sediment cores from throughout the floodplain. We discuss here paleoenvironmental analysis of sediments collected from a large U-shaped platform (U2) at the site of Rio Viejo, which was occupied from the Middle Formative to the Early Postclassic and was an urban center and political capital of the region during the Terminal Formative and again in the Late Classic. At least 3 other artificial depressions associated with mounded architecture occur at Río Viejo. These features range in size from 1-2 ha and are up to 4 m below the associated platform and at least 1 m below the level of the floodplain. The depression at U2 retains water today into the dry season. The original purpose of the features is unclear, although it is hypothesized that they were water-control features, possibly for specialized agriculture.

Continuous auger samples were collected to a depth of 3.5 m from the U2 feature. Multi-proxy data analysis was undertaken, specifically loss on ignition, macroscopic charcoal, carbon isotope, pollen and opal phytoliths. Chronology is based upon AMS radiocarbon dates and ceramics. The charcoal, pottery and carbon isotopes show a distinct pattern of site occupation and abandonment.