Late-glacial deposits on the chalk of South-East England

Abstract

Subaerial deposits of the Late-glacial Period (ca. 12000 to 8300 B.C.) of the Last Glaciation are described at a number of sites in Kent, Surrey and Sussex. The deposits are primarily stratified chalk muds and fine rubbles, produced by frost-shattering and the release of water from melting snow-fields and from frozen ground. The climatic improvement of zone II, or Allerod Oscillation (10000 to 8800 B.C.), is widely reflected stratigraphically by a rendsina soil, containing fragments of wood charcoal, separating two sheets of chalk muds referred to zones I and III. The age of the soil has been confirmed by radiocarbon dating. It is correlated with the Usselo Layer within the Younger Coversands of the Netherlands. There is evidence from two areas, Folkestone and the Medway Valley, that the climate of south-east England became sufficiently cold during zone III to produce fairly intense frost-heaving (cryoturbation). The deposits contain virtually no pollen, but yield a fauna of land Mollusca. Columns of samples were collected from six sections and the assemblages they yielded are presented in the form of histograms, showing the changing vertical abundance of each species. The fauna is a remarkable mixture of diverse zoogeographical elements; its relations are with the Alpine area rather than with the Arctic. The ecological and climatic significance of the changes in the assemblages is discussed. During zone II, the assemblages increase in variety and certain relatively thermophilous species were able to spread widely, most notably the West European and Alpine snail Abida secale. The climate of zone III was probably more humid than that of zone I, and also less cold. In Sussex, due to the proximity of the open sea to the south-west, the climate of zone I may have been relatively milder than in Kent and Surrey; this is suggested by the appearance of thermophilous species perhaps 1000 years before their general expansion on the North Downs. Evidence is put forward from several sites for a minor climatic oscillation within zone I; this is equated with the Bolling Oscillation (zone I b) of north-west Europe. The Late-glacial Period is the last for which there is evidence of active erosion in the Chalk landscape.