Temporal frequency distributions of alluvium in the American Southwest: taphonomic,paleohydraulic, and demographic implications

The use of radiocarbon frequency distributions to reconstruct prehistoric human and animal populations must account for taphonomic loss and other factors that affect the archaeological and paleontological records. Surovell et al. (JAS, 36, 1715–1724) have recently proposed a correction for “taphonomic bias” that is based on the radiocarbon frequency of a global sample of volcanic deposits. Analysis of 717 radiocarbon dates sampled from the alluvium of the San Pedro and Santa Cruz rivers and their tributaries in southeastern Arizona shows that discovery and scientific biases also play an important role in the creation of radiocarbon frequency distributions, and that the rate of “taphonomic bias” in prehistory is not predicted by the radiocarbon frequency of volcanic deposits. The latter principle is further argued using a sample of 123 Pliocene to Clovis-age proboscideans from the San Pedro Valley. We propose an alternative model that is based on the nature of the stratigraphic record, with discovery bias, scientific bias, taphonomic loss, and the shape of the calibration curve all operating to influence the temporal frequency distribution of radiocarbon-dated prehistoric phenomena.