ESTIMATING THE DURATION OF ARCHAEOLOGICAL ACTIVITY USING ¹⁴C DETERMINATIONS

Abstract

One of the questions that archaeologists have always hoped to be able to answer using radiocarbon dating is: 'How long did this activity last?'. It has for some time been accepted that this question cannot adequately be addressed by simply calibrating single radiocarbon determinations. Rather, it is necessary to find means for coherently relating such determinations to one another and to the archaeology from which they came. In addition, most archaeologists are aware that estimation of duration is likely to be greatly afected by the presence of any aberrant determinations ('outliers ') and that they should, therefore, be allowed for in the estimation procedure.In this paper we look at the issues which relate to solving problems of this type and highlight some diflculties associated with one currently available method for approaching them. By adopting a Bayesian approach to estimating duration, it is possible to provide an explicit and coherent framework within which such investigations can take place and whereby each specijk problem can be considered in its own right.In archaeological terms, this paper has, we hope, clarified the problems involved in estimating the duration of a period of time represented by a series of unordered radiocarbon determinations, and in providing estimates of the calendar dates for its beginning and end. These estimates take in any archaeological evidence available, for example, termini antelpost quos (here the arrival of the Spanish in Peru forms a terminus ante quem), and may be repeated when new evidence becomes available. For the first time, we provide an objective method for identifying outliers in the data and documenting the efect of their removal. We have given an example for the Peruvian Chancay culture to demonstrate the potential of this approach.this problem has proved difficult to tackle in the past is that it is extremely hard to make generalisations. No two situations are alike. For the purposes of this paper, however, we choose to make a very simple distinction between those situations where (before obtaining

A Novel Approach to Selecting Samples for Radiocarbon Dating

“…In previous works (for example Buck et al, 1991Buck et al, , 1994aBuck, Litton & Smith 1992;Buck, Litton & Shennan 1994b;Christen, 1994aChristen, , 1994bChristen & Litton, 1995;Zeidler, Buck & Litton, in press) we have described applications of the Bayesian radiocarbon calibration framework to a number of archaeological dating problems with prior information in a range of forms. Of particular relevance here, for example, we could recompute the risks assuming prior information of several different types (perhaps because different archaeologists had different opinions about the nature or quality of the prior information available).…”

“…The full notation and the detailed models will not be discussed here. These have been supplied, along with considerable background information, in several publications including Buck et al (1991Buck et al ( , 1994a; Buck, Litton & Smith (1992). Here we simply outline the important general features.…”

“…Over the last 5-10 years, however, a framework has been developed which allows relative chronological information to be combined with radiocarbon determinations, in a coherent and consistent manner, at the point of calibration. This framework is built around a statistical paradigm known as Bayesian statistics and a wide range of published material both theoretical and applied, now exists (see, in particular, Buck et al, 1991Buck et al, , 1994aBuck, Litton & Smith 1992;Buck, Litton & Shennan 1994b;Christen, 1994aChristen, , 1994bChristen & Litton, 1995;Zeidler, Buck & Litton, in press). …”

Rolling Out Revolution: Using Radiocarbon Dating in Archaeology

“…This was the state of 14 C dating in English archaeology in the early 1990s when the first papers outlining a new approach for interpreting 14 C dates appeared (Naylor and Smith 1988;Buck et al 1991Buck et al , 1992Buck et al , 1994aBuck et al ,b, 1996Christen 1994). The technical details of Bayesian chronological modeling will be not be covered here, as they are discussed in another paper in this volume (Bronk Ramsey, this issue).…”

New Radiocarbon Calibration Software

“…This is more complex than calibration by itself, and is typically performed via Bayesian inference (see Buck et al 1996 andChristen 1994a for an overview of this type of application). Available packages include OxCal (Ramsey 1995), Bcal (Buck et al 1999), and MexCal (Buck et al 1999), all of which are designed to perform Bayesian calibration of CRAs. These tools are more than adequate for the job at hand, if used correctly.…”