- 1 Chester Formation (CHES)
- 2 References
- Conglomerate Beds (Hull, 1860a)
- Bunter Sandstone (Hull, 1860b)
- Pebble Beds (Hull, 1860b)
- St Bees Sandstone (Harkness, 1862)
- Bunter Conglomerate/Beds (Bonney, 1880)
- Budleigh Salterton Pebble Bed (Irving, 1888)
- Budleigh Salterton Conglomerate and Sandstone (Hull, 1892)
- Bunter Pebble Beds (Bonney, 1900)
- Pebble Beds (Ussher, 1902)
- Pebble Bed Group (Wills, 1948)
- Budleigh Salterton Pebble Beds (Laming, 1968)
- Budleigh Salterton Pebble Beds Formation (Henson, 1970)
- Kidderminster Conglomerate Formation (Smith et al., 1974)
- Chester Pebble Beds Formation (Warrington et al., 1980)
- Kidderminster Formation (Warrington et al., 1980)
- Cannock Chase Formation (Warrington et al., 1980)
- Nottingham Castle Formation (Warrington et al., 1980)
- Hawksmoor Formation (Charsley, 1982)
- Polesworth Formation (Worssam and Old, 1988)
- Nottingham Castle Sandstone Formation (Charsley et al., 1990)
- St Bees Sandstone Formation (Warrington et al., 1980, Barnes et al., 1994)
Derivation of name
From the City of Chester, Cheshire; renaming the former Chester Pebble Beds Formation
The City of Chester and vicinity, Cheshire
SJ 40 71: City of Chester and vicinity (sites in Earp and Taylor, 1986).
The main sections are in Chester, on the railway line (SO 401 666 to 406 671) and the Shropshire Union Canal 9SO 401 666 to 406 6670; these show 67 to 76 m of red, cross-bedded sandstones and pebbly sandstones.
- SY 060 816: 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.
- SK 0392 4422: Hawksmoor Wood, 2.5 km east-north-east of Cheadle, Staffordshire; >11 m of cross-bedded, pebbly sandstones with thin beds of conglomerate (Chisholm et al., 1988).
- SO 83 76: Kidderminster and its vicinity, Worcestershire. Numerous exposures of conglomerate and sandstone in and around the town (Mitchell et al., 1962).
- SK 569 394: Castle Rock, Nottingham; 40 m-high former river cliff with up to 35 m of cross-bedded, pebbly sandstone exposed (Howard et al., 2009).
- SK 3010 1327: disused quarry at Acresford, Leicestershire, exposing about 10 m of interbedded cross-bedded conglomerates, pebbly sandstones and sandstone (Worssam and Old, 1988).
- SJ 303 735: Burton Point, Wirral (Steel and Thompson, 1983).
- NX 960 156 to NX 958 117: 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).
The formation is exposed on the south Devon coast, in the Dorset and East Devon Coast World Heritage Site (Barton et al., 2011), but across much of east Devon, Somerset and the south Midlands it is not exposed except in quarries. Quarries in Devon, the Kidderminster area and south Staffordshire show good exposures. There are a few exposures in north Warwickshire and south-west Leicestershire. It is well exposed in the city of Nottingham and in places throughout Nottinghamshire and South Yorkshire, up to Doncaster; the formation cannot be distinguished farther north. There are exposures in Staffordshire and Derbyshire, between Cheadle and Ashbourne, and in Cheshire. The formation is well exposed in Merseyside, particularly on the Wirral peninsula. Through Lancashire the formation is largely obscured by superficial deposits and is difficult to distinguish owing to a northward facies change from pebbly sandstones and conglomerates to sandstones. On the Cumbrian coast, the formation is very well exposed.
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.
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.
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 commonly 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.
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 to 627 m) are in Cumbria.
Early Triassic, Olenekian on magnetostratigraphical evidence (Hounslow and McIntosh, 2003) or older (Warrington, 2005).
- Rottington Sandstone Member, St Bees Sandstone Formation, East Irish Sea Basin (Jackson and Johnson, 1996; Chadwick et al., 2001).
- Smith Bank Formation (pars.), Heron Group, Central North Sea (Cameron, 1993).
- Bunter Sandstone Formation, Bacton Group, Southern North Sea Basin (Cameron et al., 1992; Johnson et al., 1994; Bachmann et al., 2010).
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.
- Freehay Member (Chisholm et al., 1988)
- Lodgedale Member (Chisholm et al., 1988)
- North Head Member (Ackhurst et al., 1997)
- Quartzite Breccia* (Old et al., 1991). The status of this unit is uncertain. It was defined by Old et al. (1991) in the Redditch district but renamed the Hopwas Breccia by Powell et al. (2000) in the Birmingham area.