Radiocarbon dates from the ‘Allerød soil’ in Kent

Abstract

In the 1960s, Kerney reported the widespread occurrence in southern Britain of a fossil rendzina soil in many chalkland valley sequences of Late-glacial age. He concluded that this soil had formed during the ‘Allerod Interstadial’, a conclusion partly supported by two conventional radiocarbon dates of c . 11 900 yr bp from Dover Hill, Folkestone and from Brook, both in Kent. AMS determinations are reported here from charcoal from the upper and lower halves of the Dover Hill palaeosol and from the equivalent horizons at Upper Halling, a previously undated site in north Kent. These determinations are significantly younger than the conventional dates and fall in the range 10 900–11 220 yr bp , which are much closer to expected values. In the case of Dover Hill, the discrepancy between the original conventional date and the new AMS dates has been shown to result largely from a simple error of transcription, Q-463 published as 11 934 ± 210 yr bp , should have been quoted as 11 550 ± 135 yr bp . This revised date fits perfectly with other AMS dates recently obtained from the same horizon in Holywell Coombe, 2 km west of Dover Hill. Some new dates are also reported from Brook. Two pairs of determinations have been measured on the ‘humic’ and ‘humin’ fractions from an organic detritus mud from ‘Borehole III’, previously dated at 11 900 ± 160 yr bp , using both conventional and AMS techniques. The results are remarkably consistent and give a pooled mean of 12 190 ± 30 yr bp . Charcoal from a ‘marsh soil’ about 15 cm above the organic detritus mud yielded an AMS date of 11 170 ± 70 yr bp . These results demonstrate that it is the ‘marsh soil’ that equates with the ‘Allerod’ soils elsewhere in Kent, and not the organic detritus mud, as previously supposed. Another AMS date of 11 575 ± 75 yr bp was obtained from the ‘Allerod soil’ at College Farm, Brook.