ESR dating of the type Cromerian freshwater bed at West Runton, U.K.

Abstract

We performed ESR dating on tooth enamel from three in situ locations within the West Runton Freshwater Bed (FW) bed, which is stratigraphically below fluvial sands of Anglian origin. The teeth contained little uranium, which made ESR ages essentially independent of the choice of uranium uptake model. However, this advantage was offset by a critical dependence of the ESR ages upon the moisture content of the sediments. Care was taken to account for self-shielding effects arising from the large size of the elephant tooth. Using the value of 10% moisture content observed during 1992 in sediments exposed on the cliff face, gives ages of 346±55 (EU) and 350±52 (LU) ka, corresponding to the Oxygen Isotope Stage 11 10 boundary. Additional moisture content measurements of different parts of the FW bed in 1995 yielded a mean value of 25%. Using values of 20 and 30% moisture content, we obtain ages from 420±90 to 460±80 ka (EU, 1σ errors). Because the faunal and floral data indicate that the FW bed was an interglacial deposit, the ESR results suggest that the FW bed could have been deposited in either isotope stages 11 or 13. However, independent faunal and stratigraphic evidence favours a stage 13 age or earlier; this is discussed in relation to the ESR data. These results are consistent with prevailing views (e.g. Bridgland, 1994) that the overlying Anglian deposits correlate with oxygen isotope stage 12.