The BGS Lexicon of Named Rock Units — Result Details
Chester Formation
| Computer Code: | CHES | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Olenekian Age (TO) — Olenekian Age (TO) | ||
| Lithological Description: | The formation shows a progressive change in lithology northwards, from a coarse-grained, typically well-cemented proximal facies to a fine-grained, less well-cemented distal facies. The Devon outcrops are closest to the presumed source, in northern France, and comprise brown, horizontally-bedded conglomerate with subordinate lenticular beds of trough cross-bedded pebbly sand and sand (Smith, 1990; Smith and Edwards, 1991). The gravel is composed of well-rounded pebbles, cobbles and boulders in a coarse to fine granulestone and silty sandstone matrix. The clasts are mainly (84 to 90 per cent) metaquartzite, together with porphyry, vein quartz, tourmalinite, and conglomerate. From just south of Hillhead, east Devon [ST 067 136], locally derived Devonian and Carboniferous clasts begin to appear. Near Milverton, Somerset, the formation is a massive calcareous conglomerate with limestone clasts. Northwards into the Worcester Basin, West Midlands, Staffordshire (Steel and Thompson, 1983), Cheshire and Leicestershire, the formation comprises conglomerates and reddish brown, cross-bedded, pebbly sandstones with subordinate beds of red-brown mudstone. The conglomerates have a reddish brown sandy matrix and consist mainly of pebbles of brown or purple quartzite, with quartz conglomerate and vein quartz. In these areas the formation generally fines upwards, from dominantly conglomerates at the base, to interbedded conglomerates and sandstones, with sandstone and pebbly sandstone predominant in the upper part, and rare mudstones. In Nottinghamshire, the formation comprises pinkish red or buff-grey, medium- to coarse-grained, pebbly, cross-bedded, friable sandstone. In north Staffordshire, it consists of red-brown, yellow, or yellow-mottled, very fine- to coarse-grained sandstones that are commonly cross-bedded, locally micaceous, silty or argillaceous, pebbly or conglomeratic, and generally friable. Northwards from Nottingham the pebbles gradually die out; the farthest north they have been seen consistently is around Doncaster. West of the Pennines they occur in the Wirral-Liverpool area but disappear farther north in Lancashire, where the formation cannot be distinguished. On the Cumbrian coast, the formation is represented by a distal facies comprising red-brown, very fine- to medium-grained, commonly micaceous sandstones, which are generally cross-bedded, with some parallel lamination; mudstone clasts are locally common and subordinate thin beds of greenish grey sandstone occur. The formation has subordinate lenticular beds of reddish brown mudstone or siltstone throughout; these are more common in Cumbria. | ||
| Definition of Lower Boundary: | The lower boundary varies across the country. The formation rests conformably, unconformably or disconformably on Permian rocks, and unconformably on rocks of mainly Carboniferous or older Palaeozoic and Precambrian age. | ||
| Definition of Upper Boundary: | The upper boundary is, in parts of the country, overlain unconformably by sandstones or pebbly sandstones of the Helsby Sandstone Formation, or generally laminated mudstones, siltstones and sandstones of the MMG. Elsewhere it is conformable and generally transitional to the Wilmslow Sandstone Formation. In places the boundary is taken arbitrarily at the gradational upward change from the highest pebble bed to the overlying silty sandstones of the Wilmslow Sandstone Formation. In Cumbria it is placed at the sharp upward change from generally fine-grained, well-cemented sandstones, with features typical of fluvial deposition, to coarser, more friable sandstones with common well-rounded aeolian grains. A feature of the Chester Formation on borehole geophysical logs is the sonic velocity which is always higher than in the bulk of the overlying formations, and often higher than in the underlying formation. The gamma-ray response is more variable. The top of the formation is not always clearly defined on the gamma-ray logs when compared to the known downhole appearance of pebbles. | ||
| Thickness: | The formation shows a wide range of thicknesses across the country. It is thinnest (less than 50 m), in Dorset, and up to 220 m in most other regions. In north Staffordshire it is up to 300 m thick; the thickest proven sequences (340-627 m) are in Cumbria. | ||
| Geographical Limits: | The formation extends from the south Devon coast northwards, up to the Cumbrian coast on the west side of England, and to the Doncaster area on the east side. From Doncaster northwards, to Teesside, and in parts of Lancashire, the Sherwood Sandstone Group is undivided. | ||
| Parent Unit: | Sherwood Sandstone Group (SSG) | ||
| Previous Name(s): | Budleigh Salterton Conglomerate And Sandstone
(-5126)
Budleigh Salterton Pebble Bed [Obsolete Name and Code: Use BSP, CHES] (-3877) Budleigh Salterton Pebble Beds Formation [Obsolete Name And Code Use: CHES] (BSP) Bunter Conglomerate Beds (-5128) Bunter Pebble Beds [Obsolete Name And Code: Use CHES] (BNP) Bunter Sandstone [Obsolete Name and Code: Use SSG, CHES] (-1199) Cannock Chase Formation [Obsolete Name And Code Use: CHES] (CCF) Chester Pebble Beds Formation [Obsolete Name And Code Use: CHES] (CPB) Conglomerate Beds (-5130) Hawksmoor Formation [Obsolete Name And Code Use: CHES] (HAW) Kidderminster Conglomerate Formation (-990) Nottingham Castle Formation [Obsolete Name and Code: Use NTC, CHES] (-3590) Nottingham Castle Sandstone Formation [Obsolete Name And Code Use: CHES] (NTC) Pebble Bed Group (-5131) Pebble Beds [Obsolete Name and Code: Use BSP, CHES] (-1399) Polesworth Formation [Obsolete Name And Code Use: CHES] (PLWF) St Bees Sandstone [Obsolete Name and Code: Use SBS, CHES] (-1162) St Bees Sandstone Member (SBS) Kidderminster Formation [Obsolete name and code, use CHES] (KDM) |
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| Alternative Name(s): | Smith Bank Formation Rottington Sandstone Member Bunter Sandstone Formation |
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| Stratotypes: | |||
| Type Area | The City of Chester and vicinity, Cheshire. | ||
| Type Section | The main sections are in Chester, on the railway line and the Shropshire Union Canal; these show 67 to 76 m of red, cross-bedded sandstones and pebbly sandstones. | ||
| Reference Section | Sea-cliff at Budleigh Salterton, south Devon; sharp base on the Littleham Mudstone Formation (Aylesbeare Mudstone Group), and overlain, above a palaeosol and ventifact bed (Wright et al., 1991), by aeolian sands at the base of the Helsby (formerly Otter) Sandstone Formation. | ||
| Reference Section | Hawksmoor Wood, 2.5km east-north-east of Cheadle, Staffordshire; >11 m of cross-bedded, pebbly sandstones with thin beds of conglomerate (Chisholm et al., 1988). | ||
| Reference Section | Kidderminster and its vicinity, Worcestershire. Numerous exposures of conglomerate and sandstone in and around the town (Mitchell et al., 1962). | ||
| Type Section | City of Chester and vicinity (sites in Earp and Taylor, 1986). | ||
| Reference Section | Castle Rock, Nottingham; 40 m-high former river cliff with up to 35 m of cross-bedded, pebbly sandstone exposed (Howard et al., 2009). | ||
| Reference Section | Disused quarry at Acresford, Leicestershire, exposing c. 10 m of interbedded cross-bedded conglomerates, pebbly sandstones and sandstone (Worssam and Old, 1988). | ||
| Reference Section | Burton Point, Wirral (Steel and Thompson, 1983). | ||
| Reference Section | Coast and quarry sections at St Bees Head, Cumbria, between Saltom Bay and St Bees, exposing >200 m of red, cross-bedded sandstones with thin mudstone beds (Benton et al., 2002). | ||
| Reference(s): | |||
| Ambrose, K, Hough, E, Smith, N J P, and Warrington, G. 2014. Lithostratigraphy of the Sherwood Sandstone Group of England, Wales and south-west Scotland. British Geological Survey Research Report RR/14/01. | |||
| Bachmann, G H, Geluk, M C, Warrington, G, Becker-Roman, A, Beutler, G, Hagdorn, H, Hounslow, M W, Nitsch, E, Röhling, H-G, Simon, T, and Szulc, J. 2010. Triassic. 148-173 in Petroleum Geological Atlas of the Southern Permian Basin Area. Doornenbal, J C, and Stevenson, A G (editors). (Houten: EAGE Publications b.v.) | |||
| Barnes, R P, Ambrose, K, Holliday, D W, and Jones N S. 1994. Lithostratigraphical subdivision of the Triassic Sherwood Sandstone Group in west Cumbria. Proceedings of the Yorkshire Geological Society, Vol. 50, 51-60. | |||
| Barton, C M, Woods, M A, Bristow, C R, Newell, A J, Westhead, R K, Evans, D J, Kirby, G A, and Warrington, G. 2011. Geology of south Dorset and south-east Devon and its World Heritage Coast. Special Memoir of the British Geological Survey, Sheets 328, 341/342, 342/343 and parts of 326/340, 327, 329 and 339. | |||
| Benton, M J, Cook, E, and Turner, P. 2002. Permian and Triassic Red Beds and the Penarth Group of Great Britain. Geological Conservation Review Series, No. 24. (Peterborough: Joint Nature Conservation Committee.) | |||
| Cameron, T D J, Crosby, A, Balson, P S, Jeffery, D H, Lott, G K, Bulat, J, and Harrison, D J. 1992. United Kingdom offshore regional report: the geology of the southern North Sea. (London: HMSO for the British Geological Survey.) | |||
| Cameron, T D J. 1993. 4. Triassic, Permian and pre-Permian of the Central and Northern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. | |||
| Chadwick, R A, Jackson, D I, Barnes, R P, Kimbell, G S, Johnson, H, Chiverell, R C, Thomas, G S P, Jones, N S, Riley, N J, Pickett, E A, Young, B, Holliday, D W, Ball, D F, Molyneux, S G, Long, D, Power, G M and Roberts, D H. 2001. Geology of the Isle of Man and its offshore area. British Geological Survey Research Report, RR/01/06. | |||
| Charsley, T J, 1982. A standard nomenclature for the Trassic formations of the Ashbourne district. Report of the Institute of Geological Sciences, No. 81/14. | |||
| Charsley, T J, Rathbone, P A and Lowe, D J, 1990. Nottingham: A geological background for planning and development. British Geological Survey Technical Report WA/90/1. | |||
| Chisholm, J I, Charsley, T J and Aitkenhead, N. 1988. Geology of the country around Ashbourne and Cheadle. Memoir of the British Geological Survey, Sheet 124 (England and Wales). | |||
| Earp, J R and Taylor, B J, 1986. Geology of the country around Chester and Winsford. Memoir of the British Geological Survey, Sheet 109 (England and Wales). | |||
| Henson, M R, 1970. The Triassic rocks of south Devon. Proceedings of the Ussher Society, Vol.2, p.172-177. | |||
| Hounslow, M W, and McIntosh, G. 2003. Magnetostratigraphy of the Sherwood Sandstone Group (Lower and Middle Triassic), south Devon, UK: detailed correlation of the marine and nonmarine Anisian. Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 193, 325–348. | |||
| Howard, A S, Warrington, G, Carney, J N, Ambrose, K, Young, S R and Pharaoh, T C. 2009. Geology of the country around Nottingham. Memoir of the British Geological Survey, Sheet 126 (England and Wales). | |||
| Hull, E. 1860. On the south-easterly attenuation of the lower secondary formations of England; and the probable depth of Coal Measures under Oxfordshire and Northamptonshire. Quarterly Journal of the Geological Society of London, Vol. 16, 63–81. | |||
| Hull, E. 1860. On the new subdivisions of the Triassic rocks of the central counties. Transactions of the Manchester Geological Society, Vol. 2, 22–34. | |||
| Hull, E, 1892. A comparison of the red rocks of the south Devon coast with those of the Midland and Western counties. Quarterly Journal of the Geological Society of London, Vol.48, p.60-67. | |||
| Jackson, D I and Johnson, H, 1996. Lithostratigraphic nomenclature of the Triassic, Permian and Carboniferous of the UK offshore East Irish Sea Basin, British Geological Survey, Nottingham. | |||
| Johnson, H, Warrington, G and Stoker, S J. 1994. 6. Permian and Triassic of the Southern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. | |||
| Laming, D J C, 1968. New Red Sandstone stratigraphy in Devon and West Somerset. Proceedings of the Ussher Society, Vol.2, p.23-25. | |||
| Mitchell, G H, Pocock, R W, and Taylor, J H. 1962. Geology of the country around Droitwich, Abberley and Kidderminster. Memoir of the Geological Survey of Great Britain, Sheet 182 (England and Wales). | |||
| Smith, S A and Edwards, R A, 1991. Regional sedimentological variations in lower Triassic fluvial conglomerates (Budleigh Salterton Pebble Beds), southwest England: some implications for palaeogeography and basin evolution. Geological Journal, Vol.26, p.65-83 | |||
| Smith, D B, Brunstrom, R G W, Manning, D I, Simpson, S and Shotton, F W. 1974. A correlation of Permian rocks in the British Isles. Geological Society of London Special Report No. 5. | |||
| Ussher, W A E. 1902. The Geology of the country around Exeter. Memoir of the Geological Survey of Great Britain, Sheet 325. (England and Wales). | |||
| Warrington, G, Audley-Charles, M G, Elliott, R E, Evans, W B, Ivimey-Cook, H C, Kent, P E, Robinson, P L, Shotton, F W and Taylor, F M. 1980. A correlation of the Triassic rocks in the British Isles. Special Report of the Geological Society of London, No.13. | |||
| Wills, L J, 1948. The palaeogeography of the Midlands. London, Liverpool. | |||
| Worssam, B C and Old, R A, 1988. Geology of the country around Coalville. Memoir of the British Geological Survey, Sheet 155 (England and Wales) | |||
| Bonney, T G. 1880. Note on the pebbles in the Bunter Beds of Staffordshire. Geological Magazine, Vol. 17, 404–407. | |||
| Bonney, T G. 1900. The Bunter Pebble Beds of the Midlands and the source of their materials. Quarterly Journal of the Geological Society of London, Vol. 56, 287–306. | |||
| Harkness, R. 1862. On the sandstones and their associated deposits in the Vale of Eden, the Cumberland Plain and the south-east of Dumfriesshire. Quarterly Journal of the Geological Society of London, Vol. 18, 205–218. | |||
| Irving, A. 1888. The red-rock series of the Devon coast section. Quarterly Journal of the Geological Society of London, Vol. 44, 149–163. | |||
| Smith, S A. 1990. The sedimentology and accretionary styles of an ancient gravel-bed stream: the Budleigh Salterton Pebble Beds (Lower Triassic, south-west England). Sedimentary Geology, Vol. 67, 199–219. | |||
| Steel, R J, and Thompson, D B. 1983. Structures and textures in Triassic braided stream conglomerates (‘Bunter’ Pebble Beds) in the Sherwood Sandstone Group, North Staffordshire, England. Sedimentology, Vol. 30, 341–367. | |||
| Warrington, G. 2005. The chronology of the Permian and Triassic of Devon and south-east Cornwall (UK): a review of methods and results. Geoscience in south-west England, Vol. 11, 117–122. | |||
| Wright, V P, Marriott, S B, and Vanstone, S D. 1991. A ‘reg’ paleosol from the Lower Triassic of south Devon: stratigraphic and palaeogeographic implications. Geological Magazine, Vol. 128, 517–523. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||