The Geological Framework of the Frome-Piddle Catchment Integrated Geoscience Surveys - Southern Britain Commissioned Report CR/02/197 N BRITISH GEOLOGICAL SURVEY COMMISSIONED REPORT CR/02/197N The Geological Framework of the Frome-Piddle Catchment Newell, A J, Royse, K R, Barron, A J M and Woods, M A The National Grid and other Ordnance Survey data are used with the permission of the Con- troller of Her Majesty’s Station- ery Office. Ordnance Survey licence number GD 272191/1999 Key words Geology, Dorset, Chalk, Palaeo- gene, Structure Front Cover Shaded relief image of the Frome-Piddle Catchment Bibliographical reference Newell, A J, Royse, K R, Barron, A J M and Woods, M A. 2002. The Geological Framework of the Frome-Piddle Catchment. British Geological Survey Com- missioned Report. 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Forde House, Park Five Business Centre, Harrier Way, Sowton, Exeter, Devon EX2 7HU 01392-445271 Fax 01392-445371 Geological Survey of Northern Ireland, 20 College Gardens, Bel- fast BT9 6BS 028-9066 6595 Fax 028-9066 2835 Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB 01491-838800 Fax 01491-692345 Parent Body Natural Environment Research Council, Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1EU 01793-411500 Fax 01793-411501 www.nerc.ac.uk Contents 1 Introduction 1 1.1 Regional Geological Setting ............................................................................................... 1 1.2 Analysis of catchment area surface geology ....................................................................... 1 2 Solid geology of the Frome-Piddle Catchment .................................................................... 3 2.1 Jurassic-Early Cretaceous Strata ......................................................................................... 3 2.1.1 Lower Jurassic strata ............................................................................................................................. 3 2.1.2 Inferior Oolite Formation ...................................................................................................................... 3 2.1.3 Fuller's Earth Formation ........................................................................................................................ 3 2.1.4 Frome Clay Formation .......................................................................................................................... 3 2.1.5 Forest Marble Formation ....................................................................................................................... 3 2.1.6 Cornbrash Formation............................................................................................................................. 3 2.1.7 Kellaways Formation ............................................................................................................................ 3 2.1.8 Oxford Clay Formation ......................................................................................................................... 3 2.1.9 Corallian Group ..................................................................................................................................... 4 2.1.10 Kimmeridge Clay Formation ............................................................................................................ 4 2.1.11 Portland Group ................................................................................................................................. 4 2.1.12 Purbeck Group .................................................................................................................................. 4 2.1.13 Wealden Group ................................................................................................................................. 4 2.2 ‘Early-Upper Cretaceous’ strata .......................................................................................... 4 2.2.1 Lower Greensand Formation ................................................................................................................. 4 2.2.2 Gault Formation .................................................................................................................................... 4 2.2.3 Upper Greensand Formation ................................................................................................................. 4 2.2.4 Chalk Group .......................................................................................................................................... 4 2.3 Palaeogene strata ................................................................................................................. 6 2.3.1 London Clay Formation ........................................................................................................................ 6 2.3.2 Poole Formation .................................................................................................................................... 6 2.3.3 Branksome Sand Formation .................................................................................................................. 6 2.3.4 Creech Barrow Limestone Formation ................................................................................................... 6 3 Drift geology of the Frome-Piddle catchment ..................................................................... 7 3.1 Clay-with-flints ................................................................................................................... 7 3.2 Head .................................................................................................................................... 7 3.3 River terrace deposits .......................................................................................................... 7 3.4 Alluvium .............................................................................................................................. 7 3.5 Subsidence hollows and sink holes ..................................................................................... 7 4 Structural Framework of the Frome-Piddle Catchment ........................................................ 8 4.1 Introduction ......................................................................................................................... 8 4.2 Notes on major structures .................................................................................................... 8 4.2.1 Abbotsbury-Ridgeway Fault ................................................................................................................. 8 4.2.2 Purbeck Fault/Disturbance .................................................................................................................... 8 i 4.2.3 Litton Cheney Fault ............................................................................................................................... 8 4.2.4 Winterbourne Abbas Fault .................................................................................................................... 8 4.2.5 Watchet-Cothelstone Fault .................................................................................................................... 8 4.2.6 Compton Valence Dome ....................................................................................................................... 9 4.2.7 Wareham Basin ..................................................................................................................................... 9 5 Structure Contour Maps .................................................................................................... 10 Appendix 1 Table showing current solid lithostratigraphic terms (black) against equivalent obsolete terms (blue) used on some 1:10 000-scale maps. ................................... 11 Appendix 2 Table of boreholes used in modelling. ........................................................... 15 Appendix 3 Modelling Data Sources ................................................................................ 19 Appendix 4 Modelling methodology ...............................................................................