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Optically stimulated luminescence ( OSL ) dating
| Content Provider | Semantic Scholar |
|---|---|
| Author | Jacobs, Zenobia |
| Copyright Year | 2016 |
| Abstract | A small programme of OSL dating was carried out at the site. Although we had some preconceptions that the probable age of the site was c MIS 11, it was important not to let this prior expectation over-ride independent chronometric investigation of the date. Furthermore, it was not known until fieldwork was substantially in progress how much other vertebrate and molluscan material (including Bithynia opercula) that could contribute to dating was present. Therefore, since the site was rich in sand/silt horizons sedimentologically suitable for OSL dating, a series of tube-samples for OSL dating was taken throughout the sequence (Table 14.1). Later, once fieldwork and some preliminary faunal analysis had been completed, it was clear that the most significant archaeological horizon of the site, the Phase 6 clay, which included the elephant skeleton and the flint scatter south of Trench D, was reliably dated to MIS 11 by both independent chronometric means (amino acid dating, Chapter 13) and biostratigraphy (Chapter 9). Therefore, when it came to determining the postexcavation programme, there was evidently little benefit in devoting resources to carrying out OSL dating on sediments that: (a) were already confidently dated to MIS 11 and (b) given this, were in any case at the upper limit of the viability of the method. Nonetheless, a small programme was carried out on some of the horizons at the top of the sequence, for which there was no other dating evidence. The highest level with molluscan and/or other biological remains allowing direct dating was the Phase 6 clay. Above this, the stratigraphic superposition of deposits of Phases 7, 8 and 9 established their relative ages, although it was uncertain whether this sequence was laid down in relatively quick succession following Phase 6, or whether it included significant chronological hiatuses. It was suspected on geo-morphological grounds that the Phase 8 gravels were probably of similar age to the Lower Middle Gravel at Barnfield Pit (ie also MIS 11). However there was no other evidence to support this (apart from, perhaps, the typology of the handaxes from the gravel (see Chapter 20), although dating deposits from their artefactual content should never be relied upon). Also, there was no evidence of a major stratigraphic unconformity between the Phase 8 gravel and the overlying brickearth of Phase 9, nor was there any indication of the date of the brickearth or of the likely passage of time between its deposition and the cessation of fluvial activity associated with the under lying Phase 8 gravels. Therefore OSL dating was initially focused on the top of the sequence, with sand-rich beds from Phases 8 and 9 being analysed (see below). When these results proved surprisingly young, it was decided to carry out a further phase of analysis that: (a) investigated a sand-rich bed at the base of the Phase 8 gravels; and (b) analysed as a control a sand-rich sample from the base of the Phase 5 gravels, well below the Phase 6 deposits that are confidently attributed to MIS 11. As discussed in more detail below, this control analysis provided a dating result significantly younger than compatible with the Phase 6 dating evidence, leading to the suspicion that some of the other OSL results might also be questionable. None theless this programme of OSL work is presented in full here, and serves as a useful and thought-provoking casestudy, demonstrating that, when independently verified by other chronometric, biostratigraphic and geomorphological means, potentially misleading results have been obtained that would otherwise have been unsuspected. As discussed below, it is therefore perhaps now necessary to treat OSL dating results with more caution, and to seek additional independent and stratigraphic controls when applying the technique. |
| File Format | PDF HTM / HTML |
| DOI | 10.4135/9781446247501.n2731 |
| Alternate Webpage(s) | https://library.thehumanjourney.net/2732/91/15-Chapter14.pdf |
| Alternate Webpage(s) | https://doi.org/10.4135/9781446247501.n2731 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
