Scarp-Face Dry Valleys near Wantage, Oxfordshire

This paper discusses the morphology of dry valleys cut into the Chalk escarpment near Wantage, and stresses the significance for their development of processes active under periglacial conditions. Investigations led to the discovery of chalky silts and rubbles which line the bottoms of the valleys and extend as fans into the Vale of White Horse. In the Vale the fans overlie Zone II (Allerod Interstadial) marker deposits. The fans were largely formed during a marked phase of physical weathering in Zone III of the Late Devensian. Erosion during this period led to the enlargement of all the valleys examined and some of the coombes may have been cut mainly in this interval. THE short, steep-sided coombes cut into the Chalk scarps of southern England have attracted much attention over a number of years. Many studies have shown the significance of structural and climatic controls for their development, but, despite a great deal of work, opinion is still divided on the importance of processes determining valley morphologies. Some researchers argue that spring sapping and 'normal' stream erosion are the principal agents involved. Advocates of this viewpoint stress headward erosion by springs and, to a lesser degree, corrosion, soil creep and slumping (Chandler, 1909; Fagg, 1923, 1954; Lewis, 1949; Pinchemel, 1954; Sparks and Lewis, 1957; Small, 1957, 1962, 1964, 1965). It is maintained that the fall in the water table which left the valleys dry can be explained either in terms of a lowering of the base level resulting from the normal processes of denudation or to a change in climate. A second school of thought emphasizes that a periglacial environment may have provided conditions conducive to the development of Chalk valleys (Reid, 1887, 1892; Bull, 1936, 1940; Kerney, Brown and Chandler, 1964; Brown, 1966; Sheail, 1971). Particular significance is attached by those supporting this view to the effects of periods of intense physical weathering, freeze-thaw processes and erosion by meltwater streams. It is, however, unfortunate that heavy emphasis has often been laid in previous interpretations on extreme views and that, apart from the studies of Sparks and Lewis (0957) and Kerney, Brown and Chandler (1964), relatively little attention has been given to the detailed relationships of superficial deposits in the vicinity of valleys. By examining the relationships between deposits and local landforms along a io km length of the Chalk escarpment between Ashbury and Sparsholt (Fig. i), this paper stresses the factors influencing valley development in this area and touches upon several of the issues raised by previous authors. Although a number of accounts have been given of the geological features and Pleistocene deposits in the Wantage area (Kay, 1934; Arkell, 1939; Sandford, 1924, 1965; Webster, 1966; Poole, et al, 1971; Jarvis, 1973), only brief mention has been made of the escarpment valleys (Arkell, 1947; Beckinsale, 1954). Arkell argued for a spring-sapping hypothesis to explain the Manger and implied that this valley was cut during Atlantic times when the water table was higher and springs flowed more copiously. THE PHYSICAL SETTING The Chalk escarpment in this area rises abruptly above the gently sloping Vale of White Horse

Archaeology · Face (sociological concept · Fault scarp · Geography · Sociology · Geological formations and processes · Geology · Geology and Paleoclimatology Research · Paleontology · Soil erosion and sediment transport

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