A LATE-GLACIAL COLLUVIAL SEQUENCE AT WATCOMBE-BOTTOM, VENTNOR, ISLE-OF-WIGHT, ENGLAND

In a dry valley near Ventnor, Isle of Wight, thick subaerial slope dep osits of Devensian Late-glacial age overlie the Chalk. The deposits ar e crudely stratified chalk muds and rubble produced by frost-shatterin g, and moved downs[ope by the release of water from melting snow-field s and frozen ground. A laterally extensive humic horizon of a rendzina soil occurs within the sequence, clearly reflecting a period of relat ive slope stability. In places this horizon divides and its upper surf ace appears to have been disturbed, possibly by cryoturbation. Micromo rphological and other analyses confirm the pedogenic origin of this hu mic horizon, but also demonstrate the occurrence of pedological featur es both above and below it. The humic horizon therefore is not a 'buri ed' soil in the strictest sense, but is part of a vertical sequence re presenting a single complex soil with transported, accretionary and we lded components. Molluscan analyses reveal that the sequence can be di vided into four local mollusc zones, showing a progressive increase in faunal diversity throughout the profile. This succession is broadly s imilar to other Late-glacial sequences described from south-east Engla nd. Minute fragments of charcoal from the lower part of the humic hori zon have yielded an AMS dale of 11690 +/- 120 yr BP, demonstrating for mation during the 'Allerod phase' of the Late-glacial Interstadial. Th is humic horizon is correlated provisionally with the 'Pitstone Soil', even though existing dates from its type-site in Buckinghamshire are somewhat younger.