Evaluating the Reliability of AMS Dates on Food Residue on Pottery from the Late Prehistoric Central Plains of North America

Abstract

ABSTRACT. Age offsets of accelerator mass spectrometry (AMS) assays on food residue taken from pottery vessels are well-documented in Europe and Asia in cultural contexts were freshwater aquatic products are attested, but are less well studied in North America. The present study examines a series of residue dates from the late prehistoric Central Plains of North America, comparing them with context dates run on annual plant remains. At least 13 of 23 assays are either incongruent with ages on annual plant remains, inconsistent among themselves within a site, or not credible for their cultural context. The conclusion is that food residue from ceramics does not produce consistently accurate dates. Some possible factors that may serve to introduce old carbon to residue samples are discussed. It also is noted that one's conclusions about the reliability of residue may be conditioned by the precision of the age determinations and by the goals of a specific chronology-building effort.

A Re-Evaluation of the Reliability of AMS Dates on Pottery Food Residues from the Late Prehistoric Central Plains of North America: Comment on Roper (2013)

“…There seems, then, no necessary chronological association between the residue and the hackberry seeds. Further, if Roper's interpretation of the residue is correct, it seems she would attribute it to the old-wood effect to which she attributes 14 C ages on charcoal of similar time depths from the region (Roper and Adair 2011;Roper 2013).…”

“…If so, the concentrations of dead carbon from fish needed to produce offsets in the hundreds of years would be unlikely. However, because Roper (2013) has not established the extent of any ancient carbon reservoirs from the period of time in question by obtaining 14 C assays on fish bone from the various drainages, we cannot calculate the DCP in fish and thus firmly establish the likelihood of significant FROs in cooking residues. Table 4 Dead carbon percent in the modeled residues in Table 3.…”

“…Roper and Adair (2011:7) listed five 14 C ages on wood charcoal from this site that range from 720 ± 110 to 1090 ± 110 BP. Roper (2013) does not compare the 14 C ages on the residues to these ages, perhaps because of their large standard deviations and the potential for an old-wood effect.…”

“…There is also considerable variation in 14 C ages from different lodges at single sites. For example, 14 C ages on maize from what are inferred to be two different lodges at 14LV1071 (Logan 1998) vary by 130 14 C yr. Roper (2013) does not explore the variances of 14 C ages on annual plants. Rather, she focuses only on offsets between 14 C ages on residues and annuals or charcoal and those that do not meet her current hypothesis of culture-history chronology when context 14 C ages are not listed.…”

“…For 14OT5, Roper (2013) treats lodges 1 and 2 as separate sites with no contextual 14 C ages. However, there are four 14 C ages on annual plants and two on wood charcoal from two other lodges at Re-Evaluation of Reliability of AMS Dates on Pottery Food Residues this site (Roper and Adair 2011:6, 11).…”