The BGS Lexicon of Named Rock Units — Result Details

Tarporley Siltstone Formation
Computer Code: TPSF Preferred Map Code: TpS
Status Code: Full
Age range: Olenekian Age (TO) — Anisian Age (TA)
Lithological Description: Heterolithic, comprising interlaminated and interbedded siltstones, mudstones and sandstones in approximately equal proportions. The siltstones are micaceous and interlaminated with mudstones or sandstones; most of the mudstones appear structureless with a blocky habit. The sandstones are mostly very fine- to fine-grained, well sorted, and micaceous. They are typically cemented by ferroan calcite or dolomite. Sandstone beds are commonly less than 0.5m thick, though composite units, consisting of several individual sandstone beds, may reach over 5m thick. Intraformational mudclast conglomerates are common, with mudclasts concentrated at the bases of sandstone beds. Conglomerates with extraformational pebbles are rare and tend to be less than 1m thick; the "Waterstones Conglomerate" of Nottinghamshire is a notable example [Elliott, 1961]. Most mudstone and siltstone beds are reddish brown, though green-grey mottles and laminae are common. Gypsum occurs sporadically in the mudstones as small nodules. The sandstones are grey-brown and substantially paler than the siltstones and mudstones. Bedding is generally planar. Most beds are tabular and laterally extensive, though channel sandstones occur and typically have incised, erosional bases. The upper surfaces of sandstones and coarse siltstones are commonly wave or current rippled; in section the sandstones are usually planar or ripple-laminated, and exhibit sporadic rootlets.
Definition of Lower Boundary: The boundary is diachronous, in most areas interdigitating with the underlying Sherwood Sandstone Group. Within individual sections the boundary is drawn arbitarily within an interbedded, generally upwards-fining gradation from the coarse-grained, cross-stratified sandstone of the underlying Sherwood Sandstone Group to the micaceous mudstone, siltstone and fine sandstone of the Tarporley Siltstone (Warrington et al., 1980). In the Nottingham area, the base of the unit is abrupt and unconformable; it is marked by a patchily distributed basal conglomerate up to 1m thick with a strong calcareous cement (Howard et al., in press; Howard, 2003). At outcrop, the boundary is typically marked by a change in soil type from the sandy soils of the Sherwood Sandstone Group to the more clayey, slightly reddish brown soils (commonly containing fragments of fine-grained micaceous sandstone) associated with the Tarporley Siltstone Formation. A concave break of slope may mark the boundary in some areas.
Definition of Upper Boundary: The boundary is diachronous, and interdigitates with the overlying Sidmouth Mudstone Formation. Within individual sections the boundary is drawn arbitrarily within an upwards-fining, interbedded succession at the level where mudstones of the overlying Sidmouth Mudstone Formation predominate over the siltstones and sandstones of the Tarporley Siltstone Formation. At outcrop, the boundary is typically marked by a change in soil type from the brown, sandy clay soils of the Tarporley Siltstone Formation to the clayey, markedly reddish brown soils of the Sidmouth Mudstone Formation. A concave break of slope is associated with the boundary in some areas.
Thickness: Varies from 20 to 60m in the East Midlands, 50 to 70m in Staffordshire to a maximum of 220m in Cheshire. The 276m-thick succession logged in the Ashley Borehole, Cheshire (Taylor et al., 1963) probably includes a substantial thickness of the overlying Sidmouth Mudstone Formation.
Geographical Limits: The outcrop extends northwards from Warwickshire through Staffordshire, Cheshire, Leicestershire and Nottinghamshire; the formation is also proved by numerous boreholes in the adjacent subcrop. To the south of a line between Wolverhampton and Coventry, the formation passes laterally by interdigitation into the uppermost part of the Sherwood Sandstone Group and has not been differentiated by mapping. To the north of the outcrop, the formation passes laterally into mudstone-dominated facies. It appears to be absent in north and west Lancashire and the central part of the East Irish Sea Basin (Jackson et al., 1987; 1995), where the Sherwood Sandstone Group is directly overlain by a silt- and sand-poor sequence typical of the bulk of the Mercia Mudstone Group farther south. However, in the Solway and Carlisle Basins, a "Waterstones lithology" has been tentatively identified (Jackson et al., 1995) and may correlate with a grey siltstone facies in adjacent offshore areas. On the East Midlands Shelf, although the formation is identified in boreholes in the Grantham and Grimsby districts (Berridge et al., 1999; Berridge and Pattison, 1994), it cannot be identified confidently farther north in the Kingston-upon-Hull district (Gaunt et al., 1992). The lateral transition into mudstone-dominated facies in Eastern England has been described by Smith and Warrington (1971). Coeval strata in the Southern North Sea Basin are in mudstone- and halite-dominated facies (Johnson et al., 1994).
Parent Unit: Mercia Mudstone Group (MMG)
Previous Name(s): Keuper Waterstones [Obsolete Name And Code: Part Of TPSF] (KW)
Sneinton Formation [Obsolete Name And Code: Use TPSF] (SNT)
Retford Formation Plus Colwick Formation (-579)
Sneinton Formation (-1872)
Woodthorpe Formation Plus Colwick Formation (-1873)
Keuper Waterstones (-2322)
Holling Member (-2500)
Waterstones (-4008)
Maer Formation (-3732)
Maer Formation [Obsolete Name And Code: Use TPSF] (MER)
Denstone Formation (-3088)
Waterstones Group (-3089)
Woodthorpe Formation Plus Waterstones Formation (-4935)
Denstone Formation [Obsolete Name And Code: Use TPSF] (DST)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Top of Formation. Radbroke Hall Borehole 562' 0" to 582' 6" (Stockport Memoir, p.150-152) SJ77NE/7. 
Reference Section  Windyharbour Borehole, Staffordshire, SK04SE/16; full sequence cored between 51.57 and 103.16m depth. Curated core held at the National Geosciences Records Centre, BGS Keyworth. Charsley, 1982. 
Type Area  Several sections, which are mostly small exposures, around the village of Tarporley, Cheshire. Earp and Taylor (1986) descibe several exposures in the vicinity of Tarporley village. 
Reference(s):
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. 
Berridge, N G, Pattison, J, Samuel, M D A, Brandon, A, Howard, A S, Pharaoh, T C and Riley, N J, 1999. Geology of the Grantham district. Memoir of the British Geological Survey, Sheet 127 (England And Wales). 
Berridge, N G and Pattison, J, 1994. Geology of the country around Grimsby and Patrington. Memoir of the British Geological Survey, Sheets 90, 91, 81 and 82 (England and Wales). 
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. 
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). 
Evans, W B, Wilson, A A, Taylor, B J and Price, D. 1968. Geology of the country around Macclesfield, Congleton, Crewe and Middlewich. Memoir of the Geological Survey of Great Britain, Sheet 110 (England and Wales). 
Gibson, W G, 1925. The geology of the country around Stoke-on-Trent. Memoir of the British Geological Survey, Sheet 123, (England and Wales). 
Howard, A S. 2003. The Permo-Triassic rocks of Nottingham. 80-91 in The Geology of the East Midlands. Geologists' Association Guide No.63. 
Howard, A S, Warrington, G, Carney, J N, Ambrose, K, Young, S R and Pharaoh, T C. In press. Geology of the country around Nottingham. Memoir of the British Geological Survey, Sheet 126 (England and Wales). 
Hull, E, 1869. The Triassic and Permian rocks of the Midland Counties of England. Memoir of the Geological Survey of Great Britain. 
Jackson, D I, Mulholland, P, Jones, S M and Warrington, G, 1987. The geological framework of the East Irish Sea Basin. 191-203 in Brooks J and Glennie, K (editors), Petroleum Geology of North West Europe. [Graham and Trotman.] 
Jackson D I, and five others. 1995. United Kingdom offshore regional report: The geology of the Irish Sea. [London: HMSO for the British Geological Survey.] 
Johnson, H, Warrington, G and Stoker, S J. 1994. Permian and Triassic of the Southern North Sea. In Knox, R W O'B and Cordey, W G (editors), Lithostratigraphic nomenclature of the UK North Sea. [Nottingham: British Geological Survey.] 
Lamplugh, G W, Gibson, W, Sherlock, R L and Wright, W B. 1908. The geology of the country between Newark and Nottingham. Memoir of the Geological Survey of Great Britain, Sheet 126 (England and Wales). 
Poole, E G and Whiteman, A J. 1966. Geology of the country around Nantwich and Whitchurch. Memoir of the Geological Survey of Great Britain, Sheet 122 (England and Wales). 
Smith, E G and Warrington, G. 1971. The age and relationships of the Triassic rocks assigned to the lower part of the Keuper in north Nottinghamshire, north-west Lincolnshire and south Yorkshire. Proceedings of the Yorkshire Geological Society, Vol.38, 201-227. 
Swinnerton, H H. 1918. The Keuper Basement Beds near Nottingham. Proceedings of the Geologists' Association, Vol.29, 16-28. 
Wills, L J, 1970. The Triassic succession in the central Midlands in its regional setting. Quarterly Journal of the Geological Society of London, Vol.126, 225-285. 
Smith, B, 1924. On the west Cumberland Brockram and its associated rocks. Geological Magazine, Vol.59, 252-257. 
Strahan, A. 1882. The geology of the neighbourhood of Chester. Memoir of the Geological Survey of England and Wales. 
Taylor, B J, Price, R H and Trotter, F M, 1963. Geology of the country around Stockport and Knutsford. Memoir of the Geological Survey of Great Britain. 
Barclay, W J, Ambrose K, Chadwick, R A and Pharaoh, T C. 1997. Geology of the country around Worcester. Memoir of the British Geological Survey, Sheet 199 (England and Wales). 
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. 
Elliott, R E 1961. The stratigraphy of the Keuper Series in southern Notinghamshire. Proceedings of the Yorkshire Geological Society, Vol.33, 197-231. 
Gaunt, G D, Fletcher, T P amd Wood, C J. 1992. Geology of the country around Kingston upon Hull and Brigg. Memoir of the British Geological Survey, sheets 80 and 89 (England and Wales). 
Howard, A S, Warrington, G, Ambrose, K, and Rees, J G. 2008. A formational framework for the Mercia Mudstone Group (Triassic) of England and Wales. British Geological Survey Research Report, RR/08/04. 
Rees, J G and Wilson, A A. 1998. Geology of the country around Stoke-on-Trent. Memoir of the British Geological Survey, Sheet 123 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E109 E137 E139 E096 E097 E098 E110 E122 E123 E124 E138
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