Some aspects of the geomorphology of three Chiltern wind-gaps

Abstract

Although there have been many publications dealing with the general geomorphology of the Central Chilterns and Vale of Aylesbury, none has yet dealt satisfactorily with the problems of the age, origin and development of the wind-gaps and their associated superficial deposits. Three gaps, the Wendover, Tring and Dagnall, have been selected for detailed study. The morphological features have been mapped on the 6 inch scale, the soils and gravels examined, and the pattern of soil series distribution related to the landforms. The various features of the gaps have then been compared, and suggestions made as to the possible evolution of the gaps. The principal hypotheses so far put forward postulate that the gaps were initiated: - 1) by pre-glacial rivers; 2) as glacial overflow channels; 3) by marine erosion in Pliocene times; 4) by pre-glacial rivers and modified by glacial melt-water. The last of these, with amplifications, seems most in accord with the field evidence accumulated in the course of the present study. Thus a hypothesis of major south-east flowing captured Mid-Tertiary consequents is submitted for the origin of the wind-gaps at Wendover and Tring. Subsequently each gap was affected by the Calabrian marine invasion and later modified both by glacial and periglacial processes. An early cold period in the Chilterns is suggested by the head deposits in the gaps and both drift and glacial gravels in the vicinity of the Tring Gap show that a tongue of Lowestoft Ice projected into the Vale of Aylesbury. At this stage, the gaps may have been modified by the passage of melt-water. The later Gipping Advance is represented by boulder clays to the north of the Vale, and extensive coombe deposits on its floor, and was possibly the agent responsible for the blocking and reversal of the former Ouzel-Dagnall consequent. Postglacially the drift has been all but removed and the coombe material dissected. In conclusion, it is shown that this sequence of events is generally compatible with that established in adjacent areas.