Prof Christopher Ramsey

Abstract:

AbstractBayesian models have proved very powerful in analyzing large datasets of radiocarbon (14C) measurements from specific sites and in regional cultural or political models. These models require the prior for the underlying processes that are being described to be defined, including the distribution of underlying events. Chronological information is also incorporated into Bayesian models used in DNA research, with the use of Skyline plots to show demographic trends. Despite these advances, there remain difficulties in assessing whether data conform to the assumed underlying models, and in dealing with the type of artifacts seen in Sum plots. In addition, existing methods are not applicable for situations where it is not possible to quantify the underlying process, or where sample selection is thought to have filtered the data in a way that masks the original event distribution. In this paper three different approaches are compared: “Sum” distributions, postulated undated events, and kernel density approaches. Their implementation in the OxCal program is described and their suitability for visualizing the results from chronological and geographic analyses considered for cases with and without useful prior information. The conclusion is that kernel density analysis is a powerful method that could be much more widely applied in a wide range of dating applications.

Abstract:

As part of a major international research project, The Times of Their Lives, a programme of radiocarbon dating and Bayesian modelling was undertaken to refine the chronology of activities in one small but important part of the extensive Late Neolithic and Bronze Age settlement on Links of Noltland on the island of Westray, Orkney. The selected area (Trench D) is well known for having produced, next to a wall, the remains of a heap of at least 15 red deer carcasses, on top of which had been placed a large cod, a gannet’s wing along with part of a greater black-backed gull, and a pair of large antlers. This remarkable deposit had been preceded by, and was followed by, periods of cultivation and the deposition of domestic refuse. Refined date estimates have been produced, based on 18 radiocarbon determinations obtained from 16 samples from Trench D (including nine newly obtained dates, three from individual deer in the heap). These clarify when, during this long sequence of activities, the deer were heaped up: probably in the 22nd century cal bc, around the same time as Beaker pottery was deposited elsewhere on the Links. This allows comparison between the dated activities in this part of the site with activity elsewhere on the Links and also with other episodes of deer deposition in 3rd-millennium cal bc Orkney. It encourages exploration of the possible reasons for what appears to be a remarkable act of structured deposition. The significance of an earlier, much larger scale deposit featuring cattle remains at Ness of Brodgar is discussed in exploring the nature of Orcadian society and practices during the second half of the 3rd millennium cal bc.

Abstract:

The 60 AMS 14C determinations on cremated and non-burnt human bone presented here have provided a robust chronological framework for the interpretation of the main use phase at Knowth. This large series was seen as necessary to overcome the problem presented by the late fourth-millennium BC calibration plateau. To a large extent this strategy has been successful, but as is usually the case with modelling, there is not necessarily a single, clear-cut answer to questions of chronology, and much still depends on archaeological interpretation. Although the use of individual tombs is more variable, largely because of smaller sample sizes, overall modelling of funerary activity at Knowth consistently places the main phase of use as lasting between 100 and 300 years, maximum, in the period 3200-2900 BC (in a statement that now appears prescient, George Eogan (1991, 112) more than two decades ago suggested a date range of 3200-3000 cal. BC for the main phase of passage tomb construction and use at Knowth).