DATING HUMAN OCCUPATION ON DIATOM-PHYTOLITH-RICH SEDIMENT: CASE STUDIES OF MUSTANG SPRING AND LUBBOCK LAKE, TEXAS, USA

摘要

The Great Plains of North America have a rich archaeological record that spans the period from Late Glacial to Historic times, a period that also witnessed significant changes in climate and ecology. Chronometric dating of archaeological sites in many areas of the Great Plains, however, is often problematic, largely because charcoal and wood-the preferred materials for radiocarbon dating-are scarce in this grassland environment with few trees. Two reference archaeological sites are studied here: Mustang Spring and Lubbock Lake, Texas, USA. We carry out a geochronological approach based on a cross-study of carbon-derived data: combustion yield, δ~(13)C, ~(14)C age differences between high temperature and low temperature released carbon, and the ~(14)C age itself. A study that incorporates multiple approaches is required to solve issues induced by the sedimentological context, which is rich in both freshwater diatoms and phytoliths from quite different origins. Analysis of carbon-derived data allows us to draw a succession model of dry and wet episodes and to associate it with a chronological framework. In this way, we can assert that, for the Mustang Spring site, several human occupations existed from～11 kyr BP to ～8.7 kyr BP along the 110-cm-long series with an interruption of ～150 yr that is associated with a palustrine environment between the Plainview and Firstview occupations.