Origin of an esker-like ridge — erosion or channel-fill? Sedimentology of the Monington ‘esker’ in Southwest Wales

Abstract

A ridge of stratified gravel and sand near Cardigan in southwest Wales has previously been interpreted as an esker. Its sedimentology is exposed in sand pits and consists of cross-bedded gravel and sand incised into a complex of climbing ripple cross-laminated sand interbedded with silt and clay. The succession records the progradation of fluvial channels across a former lake floor. There is no clear sedimentological evidence that the sediments were deposited in an ice-contact setting and therefore the feature should not be called an esker. The interpretation favoured here is that the ridge is an erosional remnant, either of a formerly more extensive outwash plain, or of a kame terrace deposited when the adjacent valley was filled with dead ice. Recognition of an esker needs to be based on sedimentology and regional setting as well as on geomorphology.