Pre-Devensian glaciation of Lincolnshire (eastern England) and adjacent areas

Abstract

Recent work by several authors relating to older (pre-Devensian) glacial deposits in eastern England is evaluated. Different interpretations of till stratigraphy and lithology, pattern of ice flow, and age of the deposits render necessary an examination of the various methods and techniques employed. Perrin, Rose and Davies concentrated on till matrix analysis (Perrin et al., 1979), but their data and its spatial representation could be unduly influenced by sampling bias, and interpretation of their results weakened by failure both to acknowledge that North Sea ice followed several routes into eastern England and to appreciate the variety of materials that contributed to the tills. Field observations permit identification of several till facies and determination of distinctive assemblages of clasts of local rocks which in turn allow the inference of specific directions of ice flow. These, referable to the later phases of glaciation, are shown to be generally southward, in contrast to the massive movement of ice through the Wash gap and west and northwest over Lincolnshire claimed by Perrin et al. (1979). Such contrasting patterns might be reconciled if tills belong to different glaciations as claimed by some workers. However, an argument is presented for a Wolstonian age for the tills in Lincolnshire and around the Fenland, and is extended to consider the limit to which the Wolstonian ice sheet reached. Because general southerly flow of ice over Lincolnshire does not account for the transfer of north Lincolnshire rocks to the West Midlands, a dynamic model for the pattern of ice flow during the Wolstonian glaciation of eastern England is outlined. In this model the central mechanism comprises North Sea ice crossing the northern Lincolnshire Wolds, in force, to occupy central and northwest Lincolnshire and the lower Trent valley before being replaced and deflected southwest and south by the more powerful Vale of York ice, while coastal North Sea ice passed over the central Lincolnshire Wolds, the Wash gap and west Norfolk to reach the Brecklands and Cambridgeshire.