The BGS Lexicon of Named Rock Units — Result Details

Helsby Sandstone Formation

Computer Code: HEY Preferred Map Code: Hey
Status Code: Full
Age range: Anisian Age (TA) — Anisian Age (TA)
Lithological Description: Fine- to medium-grained, locally micaceous, cross-bedded and flat-bedded sandstones, weathering to sand near surface. Sandstones are of fluvial (sub-angular to sub-rounded grains) and aeolian (well-rounded grains) facies. Pebbles may be common, particularly near the base of the formation, and thin units of hard intraformational conglomerate occur in the south-west. Thin lenticular beds of reddish brown siltstone and mudstone occur and may be common in fining-upward sequences; calcretes and rhizocretions occur at some horizons in the south-west (Purvis and Wright, 1991; Hounslow and McIntosh, 2003; Newell, 2006).
Definition of Lower Boundary: Rests disconformably on the Wilmslow Sandstone Formation and unconformably on the Chester Formation in different areas of the country. In the west Midlands and Lancashire, it is placed at the base of the lowest pebbly bed or conglomerate. In Cumbria, it is placed where aeolian sandstones overlie a thick fluvial sandstone sequence assigned to the Wilmslow Sandstone Formation. It is not a formational boundary with characteristic features on borehole geophysical logs.
Definition of Upper Boundary: Transitional into the overlying Tarporley Siltstone Formation or, where that is absent, the Sidmouth Mudstone Formation of the MMG.
Thickness: It is locally absent in areas that were contemporary high ground such as Charnwood Forest, Breedon Hill and Mountsorrel, and possibly the Lickey Hills. The formation is thinnest in the Warwickshire, Derbyshire and north Staffordshire areas. The thickest known development (up to 500 m) is in the Worcester Basin. It thins northwards to around 250 m in the Cheshire - Lancashire area and is 90 to over 176 m thick in Cumbria. The maximum known thickness there is 176.42 m in the Sellafield 13B borehole where the top was not proved.
Geographical Limits: The formation crops out almost continuously from the south Devon coast, northwards, to near Taunton, Somerset. There is one outcrop in north-west Gloucestershire around Newent, and extensive outcrops in north Worcestershire and in Staffordshire, up to near Stoke-on-Trent. There is continuous outcrop from Warwick to Nuneaton with outcrops elsewhere in Warwickshire and extensive but broken outcrops in south Derbyshire and north-west Leicestershire, including the north side of Charnwood Forest. Further fragmentary outcrops occur in Cheshire and south-west of Manchester, with more continuous outcrops around Merseyside and in southern Lancashire. The formation crops out very locally on the Cumbrian coast and more extensively in the Eden valley.
Parent Unit: Sherwood Sandstone Group (SSG)
Previous Name(s): BASEMENT BEDS
Alternative Name(s): none recorded or not applicable
Reference Section  Bromsgrove, north Worcestershire (Warrington, et al., 1980); basal Burcot Breccia exposures (Wills, 1976, p 37); other localities (Old, et al., 1991, p 18-30).  
Reference Section  Small outcrops in river banks north of Longtown, Cumbria (Dixon et al, 1926). 
Reference Section  Sellafield Borehole 13B, Cumbria. BGS Registered No. NY00SW/42 
Type Section  Helsby Hill, Cheshire (Earp and Taylor, 1986, p.26; Thompson, 1970). 
Reference Section  Between Hollington and Alton, Staffordshire 
Reference Section  Sea cliffs between Budleigh Salterton and Sidmouth,south Devon (Hounslow and McIntosh, 2003).  
Thompson, D B, 1970. The stratigraphy of the so-called Keuper Sandstone Formation (Scythian-?Anisian) in the Permo-Triassic Cheshire Basin. Quarterly Journal of the Geological Society of London, Vol.126, p.151-181. 
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. 
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). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E109 E123 E137 E096