Oxidizable carbon ratio dating is a method of dating in archaeology and earth science that can be used to derive or estimate the age of soil and sediment samples up to 35,000 years old. The method is experimental, and it is not as widely used in archaeology as other chronometric methods such as radiocarbon dating.
Contents
The methodology was introduced by Archaeology Consulting Team from Essex Junction in 1992.
Process
This dating method works by measuring the ratio of oxidizable carbon to organic carbon. If the sample is freshly burned there will be no oxidizable carbon because it would have all been removed by the combustion process. Over time this will change and the amount of organic carbon will decrease to be replaced by oxidizable carbon. By measuring the ratio of oxidized carbon to organic carbon (the OCR) and applying it to the following equation the age of the sample can be determined with a very low standard error.
Evaluations and applications of the method
It is important to note that the OCR dating method is, like any scientific procedure, subject to testing, evaluation, and refinement.
The Oxidizable Carbon Ratio method was the subject of a Point–CounterPoint feature of the Society for American Archaeology Bulletin in 1999. In that article, Killick, Jull, and Burr suggest that the OCR method has (1) never been described in a peer-reviewed journal article, (2) that no "scientifically acceptable" demonstration of the accuracy and precision of OCR dating has been published, and (3) that the equation underlying the OCR method is questionable because of site-specific environmental factors. Frink's rejoinder to these comments points out that (1) the OCR method has indeed been described in a peer-reviewed journal article, (2) that the accuracy and precision of the method have been reported in multiple venues and that the concept of "scientifically acceptable" is context- and person-specific (and therefore a red herring), and that (3) the equation underlying the OCR method takes into account the seven factors of soil formation, and that these factors are routinely used in soil science applications without question. In the end, Frink concludes that the OCR method—like any scientific advance—warrants further study, and he points out that even the now venerable "scientifically acceptable" method of radiocarbon dating was much maligned when it was first introduced.
Frink and others have published multiple studies demonstrating that OCR dates can correlate well with radiocarbon dates (see list of published references provided below). Fullen's study of the Sarah Peralta site in Louisiana found that the OCR method served as an effective means of inferring time at the site in the absence of radiometrically dateable charcoal. He concludes that whereas debate remains concerning the OCR procedure, "the well-corroborated dates that the LSU Museum of Natural Science has had returned on material processed with OCR and conventional radiocarbon dating...the dates returned on material from Zone 3 will be considered accurate until such time that OCR dating is proven invalid." (ibid. p. 65)
The OCR method has been used in a large number of archaeological and geomorphological studies, and an incomplete list of published references is provided below. It has been used to evaluate soil development in a range of temperature regimes including arid, semi-arid , thermic, mesic, and frigic. It has also been applied to a variety of landforms including stratified fluvial deposits, desert pavements and vessicular soils, and glacial deposits. Analyses also include monumental earthworks and geoglyphs.