The Pleistocene geology and geomorphology of three gaps in the Midland Jurassic escarpment

Abstract

Previous literature is reviewed and field and laboratory methods are discussed in relation to four areas. The type area of the Itchen drainage basin reveals the composite nature of ice movement within one glacial period. Shallow facies deposits of glacial Lake Harrison have been located and a spillway into the Cherwell, associated with a lake bench at 410 ft. O.D., is considered to have been cut after most of the Older Drift had been deposited. Morphological features and gravel deposits along the Cherwell are described and a tentative link established between the sequence on the Itchen and Avon and that published for the Lower Cherwell-Upper Thames. In the Moreton gap, deposits are related to the history of Lake Harrison. Clays were laid down during the advance of the ice in an 'extra-morainic' lake, while a lake bench is related to a later 'inter-morainic' lake. Possible gaps in the Daventry-Kilsby-Rugby area are obscured by thick drift but glacial spillways may formerly have existed. The evidence suggests several possible overflows from Lake Harrison during the ice advance. The lake ceased to exist when the ice-front reached Moreton-in-the-Marsh but was re-established during the subsequent retreat. At least two levels of ponding and two points of overflow occurred at this time, before damming was suddenly ended and erosion of the present landscape commenced. The sequence of events in Lake Harrison is related to the rivers Cherwell, Evenlode, Stour and Itchen and correlated with those established for the Upper Thames, the Severn-Avon, and other areas.