The BGS Lexicon of Named Rock Units — Result Details

Tarporley Siltstone Formation

Computer Code: TPSF Preferred Map Code: TpS
Status Code: Full
Age range: Anisian Age (TA) — 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 0.5 m thick, though composite units, consisting of several individual sandstone beds, may reach over 5 m 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 1 m 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. On palynological evidence, the formation is Mid Triassic (Anisian) in age.
Definition of Lower Boundary: The boundary is diachronous, and in most regions there is interdigitation with the underlying Sherwood Sandstone Group. Within individual sections, the boundary is drawn arbitrarily within an interbedded, generally upward-fining gradation at the level where the micaceous mudstones, siltstones and fine sandstones of the Tarporley Siltstone predominate over the coarser grained, cross-stratified sandstone of the underlying Sherwood Sandstone Group (Warrington et al., 1980). Locally, for example above the Kibblestone Formation of the Stafford Basin (Rees and Wilson, 1998), the lowest part of the formation is dominated by sandstones. In these circumstances, the boundary is placed at the base of micaceous, flaggy and fine-grained sandstones, typical of the Tarporley Siltstone Formation, but differing markedly from the coarser, cross-stratified sandstones in the underlying Sherwood Sandstone Group. In the Cheshire Basin the junction between the Tarporley Siltstone Formation and the underlying Helsby Sandstone Formation is complex, being both transitional and diachronous, and locally there is a lateral passage between the two formations. For example, in the south-east of the basin, in the Stoke-on-Trent district (Rees and Wilson, 1998), siltstones, mudstones and thin sandstones (like those of the Tarporley Siltstone) alternate with thicker sandstones of Helsby Sandstone type; here the finer grained lithologies are included within the latter formation. This succession passes laterally into one where mudstones are dominant, assigned to the Tarporley Siltstone Formation. In the Nottingham area, the base of the unit is unconformable and is marked by a patchily distributed basal conglomerate up to 1 m thick with a strong calcareous cement (Howard, 2003; Howard et al., 2009). Where not exposed, the boundary is typically marked by a change in soil type from the sandy soils of the Sherwood Sandstone Group to the heavier, brown sandy clay 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. Where not exposed, 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 60 m in the East Midlands, 50 to 70 m in Staffordshire to a maximum of 220 m in Cheshire. The 276 m-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. Where, south of that line, correlatives of the formation have been recognised, for example the Sugarbrook Member of the Redditch area (Old et al., 1991), they are typically included in the upper part of the Sherwood Sandstone Group and have not been mapped separately. An exception is the Holling Member of the Worcester area, included in the Eldersfield (now Sidmouth) Mudstone Formation by Barclay et al. (1997) and here re-assigned to the Tarporley Siltstone Formation. To the north of the outcrop, the formation passes laterally into a 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). 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 confidently identified 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 (Cameron et al., 1992; Johnson et al., 1994).
Parent Unit: Mercia Mudstone Group (MMG)
Previous Name(s): Waterstones [Obsolete Name and Code: Use DST, SGBK, TPSF] (-4008)
Maer Formation [Obsolete Name and Code: Use TPSF] (MER)
Woodthorpe Formation plus Colwick Formation [Obsolete Name and Code: Use TPSF] (-1873)
Denstone Formation [Obsolete Name and Code: Use TPSF] (DST)
Sneinton Formation [Obsolete Name And Code: Use TPSF] (SNT)
Holling Member [Obsolete Name and Code: Use TPSF] (-2500)
Keuper Waterstones [Obsolete Name and Code: Use TPSF] (KW)
Retford Formation plus Colwick Formation [Obsolete Name and Code: Use TPSF] (-579)
Waterstones Group [Obsolete Name and Code: Use TPSF, SGBK, HEY] (-3089)
Woodthorpe Formation plus Waterstones Formation [Obsolete Name and Code: Use TPSF] (-4935)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Windyharbour Borehole, Staffordshire (SK 04SE/16) [SK 0854 4100] between 51.57 and 103.16 m. (Charsley, 1982). Curated core held at the National Geosciences Records Centre, BGS, Keyworth. 
Reference Section  Cropwell Bridge Borehole (SK63NE/28) [SK 6773 3547], Nottinghamshire between 170.70 and 214.33 m (Charsley et al., 1990; Howard et al., 2009). Curated core held at the National Geosciences Records Centre, BGS, Keyworth. 
Reference Section  Fulbeck F/B1 Borehole, Lincolnshire (SK 85SE/25) [SK 8889 5053] between 301.58 and 375.24 m (Berridge et al., 1999). Curated core held at the National Geosciences Records Centre, BGS, Keyworth. 
Partial Type Section  Surface section, former railway cutting, Colwick Road, Sneinton, Nottingham [SK 5924 3968 to 5920 3980]. Exposes lower boundary and lowermost 20 m of the formation (Charsley, 1989; Benton et al., 2002; Howard, 2003; Howard et al, 2009). 
Type Area  Several sections (mostly small exposures) around the village of Tarporley, Cheshire (Warrington et al., 1980). Earp and Taylor (1986) descibe several exposures in the vicinity of Tarporley village. 
Reference(s):
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. 
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. 
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). 
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. 
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). 
Jackson, D I et al. 1995. United Kingdom offshore regional report: the Geology of the Irish Sea (London: HMSO for the British Geological Survey). 
Gaunt, G D, Fletcher, T P and 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). 172pp. 
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.) 
Charsley, T J. 1989. Geology of the Nottingham (south) district: 1:10,000 Sheet SK63NE and part of 1:50,000 Sheet 126 (Nottingham) and Sheet 142 (Melton Mowbray). British Geological Survey Technical Report, Onshore Geology Series, 89/4. 
Old R A, Hamblin, R J O, Ambrose, K, and Warrington G. 1991. Geology of the country around Redditch. Memoir of the British Geological Survey, Sheet 183 (England and Wales). 
Wills, L J. 1976. The Trias of Worcestershire and Warwickshire. Report of the Institute of Geological Sciences, No.76/2. 
Benton, M J, and three others. 1994. A review of the British Middle Triassic tetrapod assemblages. 131-160 in In the shadow of the dinosaurs. Fraser, N C, and Sues, H-D (editors). (Cambridge: University Press, Cambridge.) 
Smith, B. 1912. The Green Keuper Basement Beds in Nottinghamshire and Lincolnshire. Geological Magazine, Vol. 59, 252-257. 
Warrington, G. 1970. The stratigraphy and palaeontology of the 'Keuper' Series of the central Midlands of England. Quarterly Journal of the Geological Society of London, Vol. 126, 183-223. 
Warrington, G, and four others. 1999. Stratigraphy and sedimentology. 10-40 in The Cheshire Basin: basin evolution, fluid movement and mineral resources in a Permo-Triassic rift setting. Plant, J A, Jones, D G, and Haslam, H W (editors). (Keyworth, Nottingham, British Geological Survey.) 
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. 
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. 
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). 
Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. 
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). 
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). 
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. 2009. 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.] 
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. 
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