Geology of the Devizes district : sheet description for the British Geological Survey 1:50 000 Series Sheet 282 (England and Wales)

This Sheet Description provides a summary of the geology for the area of 1:50 000 Sheet 282 Devizes. The Devizes district extends over approximately 600 km2 of north-east Wiltshire, covering much of Salisbury Plain in the south and most of the Vale of Pewsey in the north. Jurassic, Cretaceous and Palaeogene strata crop out at surface and Quaternary deposits include alluvium, peat, river terraces and head. A full account of the stratigraphy is given in this report, based on recent mapping and also drawing from an extensive archive and previous publications. Concealed strata that have been proved in deep boreholes are also included in the description. The Oxford Clay Formation and the Corallian Group, of Jurassic age, crop out in the extreme north-west of the district, beyond a major fault. The uppermost part of the Jurassic; the Kimmeridge Clay formation, Portland and Purbeck groups, crop out in the north-west near Devizes. However, Cretaceous rocks underlie most of the district: the Weald Clay, Lower Greensand, Gault and Upper Greensand formations of the Lower Cretaceous and the Grey Chalk and White Chalk subgroups of the Upper Cretaceous. Palaeogene strata are rare, preserved only as a single isolated outlier capping Sidbury Hill, near Tidworth. T he Quaternary deposits are described in relation to their mode of origin and they include the residual deposits, fluvial and organic deposits, and artificial ground. A section is devoted to applied geological issues such as geotechnical factors that should be taken into consideration in any land development, for example, landsliding has affected the Upper Greensand escarpment in the north-west of the district. The chalk is a major aquifer in the district and an account of its hydrogeology is given. Other resources described include sand and gravel, building stones and brick clays. The Information Sources lists all the BGS publications relevant to the district and gives information on how to gain access to BGS collections and databases, including borehole records, geophysical, geochemical and geotechnical data