J Archaeol Sci 30 (8)

The sub-pixel spectral detectability of obsidian and ceramic artefacts against typical soil backgrounds from two study areas were analytically evaluated to determine the usefulness of remote sensing as a tool for artefact detection [in the visible (VIS), near-infrared (NIR), and/or thermal-infrared (TIR) portion of the spectrum]. In the VIS/NIR, surface concentrations of pottery needed to be 85% or greater to be detected against backgrounds of soil, rock, and vegetation. At the same wavelengths, obsidian is spectrally similar to shade and cannot be uniquely detected unless the effects of shade are independently removed. In cases where shade is not a major factor, obsidian at concentrations of 2-3% can be detected. In the TIR, pottery thresholds ranged from 12% to 48%, depending on the composition of the background. Obsidian detection thresholds ranged from 4% to 25% cover. These results indicate that surface mapping using remote sensing in the TIR has the potential to be an effective tool for prioritizing large areas for future ground surveys. USA sites used as test case.

Describes artificial heating experiments that were used as a model for the events that give rise to archaeological assemblages of charred grains. Samples of Triticum aestivum L. seeds were heated at 150, 200, 225 and 250 °C for periods of up to five hours. There were two distinct patterns of weight loss during heating, one due to expulsion of water and the other involving more substantial organic changes. Blue fluorescing material, typical of the intermediate compounds in the Maillard reaction, was observed after longer periods of heating and/or exposure to the higher temperatures. At each temperature there was a sharp initial decrease in the DNA content of the seeds followed by a gradual reduction in the rate of decay. At 150 and 200 °C, the DNA decay appeared to level off with very little additional breakdown occurring after two hours, but at 225 and 250 °C the DNA content of the seeds reached undetectable levels at some point during the heating period. Polymerase chain reactions (PCRs) were used to study the degradation of the nuclear and mitochondrial genomes. PCRs were successful with seeds heated at 150 and 200 °C for all time points up to and including 5 hours. At 225 and 250 °C, both PCRs failed after shorter periods of heating. The mitochondrial product was more resistant to heating, as expected as the mitochondrial genome is present at a higher copy number than the nuclear genome. PCR products from the mitochondrial locus were cloned and sequenced to determine if heating had any effect on the accuracy of sequence information obtained from charred wheat seeds. The frequencies of sequencing errors were similar, and low, in all six samples that were studied. All aspects of seed and DNA degradation were delayed in low-oxygen samples compared with the equivalent aerobic material.