Molluscan evidence for differentiation of interglacials within the ‘Cromerian Complex’

Abstract

Usage of the term ‘Cromerian’ differs between countries. In the Netherlands, four interglacial stages (and associated cold stages) are included within the so-called ‘Cromerian Complex’. In Britain, where the Cromerian stratotype is located, all ‘Cromerian’ sites have, until fairly recently, been attributed to different parts of a single interglacial stage. The first suggestion that this view might over-simplify reality was based on vertebrate evidence, in particular the occurrence of Arvicola terrestris cantiana, rather than Mimomys savini, in some deposits. Molluscan assemblages also exhibit significant differences between sites that have been attributed to the same interglacial stage. Valvata goldfussiana appears to characterize fluvial assemblages in the early part of the Cromerian Complex, whereas Valvata naticina typifies several of those that occur later. Combining molluscan and vertebrate evidence, it seems likely that as many as five distinct stages have been conflated and that the stratotype at West Runton occurs early in the Cromerian Complex, rather than immediately preceding the Anglian Stage.