Sherwood Sandstone Group
| Sherwood Sandstone Group | |
|---|---|
| Stratigraphic range: | |
 St Bees Sandstone, St Bees South Head, Cumbria | |
| Type | Group |
| Unit of | New Red Sandstone Supergroup |
| Sub-units | Hopwas Breccia Formation, Chester Formation, Wilmslow Sandstone Formation, Helsby Sandstone Formation Formation |
| Underlies | Mercia Mudstone Group |
| Overlies | Roxby Formation, Cumbrian Coast Group, Aylesbeare Mudstone Group and others |
| Thickness | over 2000m |
| Lithology | |
| Primary | sandstone |
| Other | conglomerate, siltstone, mudstone |
| Location | |
| Country | United Kingdom |
| Extent | widespread |
| Type section | |
| Named for | Sherwood Forest |
The Sherwood Sandstone Group is a Triassic lithostratigraphic group (a sequence of rock strata) which is widespread in Britain, especially in the English Midlands. The name is derived from Sherwood Forest in Nottinghamshire which is underlain by rocks of this age.[1] It has economic importance as the reservoir of the Morecambe Bay gas field,[2] the second largest gas field in the UK[3], and the Wytch Farm oil field in Dorset, the largest onshore oilfield in Western Europe. [4]
Geographical extent
[edit]In Northwest England, the Sherwood Sandstone Group is found in Carlisle and in the Vale of Eden. It extends down the Cumbrian coast, into Lancashire and Cheshire. It is mostly obscured by superficial deposits but the highest coastal cliffs in northwest England at St Bees Head are formed in the Chester Formation, the lowermost formation within the group.[5]. Offshore to the west, the Sherwood Sandstone Group is also present as the bedrock underneath much of the eastern Irish Sea, as well as the northeastern Isle of Man.[6]
The Sherwood Sandstone is also found in southern Scotland around Annan and Gretna).
The Sherwood Sandstone is also found in Northern Ireland, although much of the unit is buried beneath younger rocks [7]. The Sherwood Sandstone crops out north and east of Limavady, east of Cookstown, between Dungannon and Armagh and along the Lagan Valley beneath Belfast and Newtownards and on the Antrim coast.[8]
In northeastern England, the Sherwood Sandstone Group extends from Hartlepool south through the Vale of Mowbray and the Vale of York, then south through Nottinghamshire into the English Midlands, though is largely concealed by superficial sediments.
The Sherwood Sandstone occurs widely through the Midlands and notably in an outlier at Leek, Staffordshire [9].
Southwards, the Sherwood Sandstone is continuously present beneath Worcestershire, Gloucestershire, Wiltshire and Hampshire, and beyond there through Somerset, Dorset and Devon, however outcrops are very limited and it is largely buried under younger sedimentary rocks [10]. The only substantial outcrop in this area is the cliff section from Budleigh Salterton[11] to Ladram Bay and Sidmouth [12] on the coast of East Devon.
The Group comprises different sequences in each of the various basins in which it is developed as described below.
Cheshire Basin rock succession
[edit]The sequence is most thickly developed in the Cheshire Basin, which also extends into north Shropshire. It comprises the following formations:
Helsby Sandstone Formation
[edit]The Helsby Sandstone Formation (named from the Cheshire village of Helsby where the type section is exposed at Helsby Hill) comprises around 250m thickness of sandstone with conglomerate and siltstone which occurs across the Cheshire Basin. Older literature includes it as part of the Lower Keuper Sandstone.[13] It is often divided into an upper Frodsham Member and a lower Delamere Member.[14] Faulted blocks of these rocks are largely responsible for the prominent west facing escarpment of the Mid Cheshire Ridge and the Helsby Sandstone is exposed in numerous localities here, southwards from Runcorn through Frodsham to Utkinton, spectacularly at the outlier of Beeston Castle hill and lastly within the Peckforton Hills.[15]
Wilmslow Sandstone Formation
[edit]The Wilmslow Sandstone Formation (named from the town of Wilmslow in Cheshire) comprises up to 900m thickness of early Triassic sandstones with occasional siltstones. It was earlier known as the Upper Mottled Sandstone.[16] In Wirral, the 60m thick Thurstaston Sandstone Member and the 2m thick Thurstaston Hard Sandstone Bed are distinguished at the top of the sequence.[14]
Chester Formation
[edit]The Chester Formation (named from the city of Chester) comprises sandstones with some conglomerates and siltstones of early Triassic age. It ranges from less than 90m to over 220m in thickness. It has been known in the past as the Bunter Pebble Beds and the Chester Pebble Beds Formation. There are a couple of reference sections for this sequence in the vicinity of Chester.[17]
Kinnerton Sandstone Formation
[edit]The Kinnerton Sandstone Formation (named from the twin villages of Higher and Lower Kinnerton on the England/Wales border west of Chester) is a sequence which ranges from 0m to over 150m thickness of largely aeolian sandstones of early Triassic age. It was formerly known as the Lower Mottled Sandstone.[18]
English Midlands rock succession
[edit]Helsby Sandstone Formation
[edit]Once known locally as the Bromsgrove Sandstone Formation (from the town of Bromsgrove in Worcestershire), the Helsby Sandstone Formation is early Triassic to Anisian in age and comprises variously coloured sandstones whose bases are frequently conglomeratic, together with mudstones and siltstones. The thickness of the formation is variable but reaches around 500m in the Worcester area. It is often encountered in older literature as the Lower Keuper Sandstone.[19] The formation includes the Shepshed Sandstone Member.[20]
Wildmoor Sandstone Formation
[edit]The Wildmoor Sandstone Formation (named from the Worcestershire locality of Wildmoor, north of Bromsgrove) is a 0 - 284m thick sequence of sandstones formerly known as the Upper Mottled Sandstone or Wildmoor Beds. It also includes some mudstones and siltstones.[21]
Kidderminster Formation
[edit]The Kidderminster Formation (named from the Worcestershire town of Kidderminster) is a 0 - 200m thick sequence of conglomerates and sandstones previously known as either the Bunter Pebble Beds or the Kidderminster Conglomerate Formation.[22]
Chester Formation
[edit]Formerly known locally as the Polesworth Formation (from the Warwickshire village of Polesworth), the Chester Formation here is of ?Olenekian to Anisian age.
Moira Formation
[edit]The Moira Formation (named from the Leicestershire village of Moira) is of Induan/Olenekian age. Also encountered as the Hopwas or Moira Breccia.[23]
Lenton Sandstone Formation
[edit]The Lenton Sandstone Formation (named from the Nottingham suburb of Lenton) is of Induan/Olenekian age.
Stafford Basin rock succession
[edit]The Stafford Basin includes the Kibbleston Formation (named from the Staffordshire locality of Kibbleston) which is underlain by the Wildmoor Formation which is in turn underlain by the Kidderminster Formation.[24]
Needwood Basin rock succession
[edit]The rock succession in the Needwood Basin includes the Hollington Formation (named from the Staffordshire locality of Hollington) which is underlain by the Hawksmoor Formation (named from the Staffordshire locality of Hawksmoor) which includes the Hulme Member, a conglomerate and which is in turn underlain by the Huntley Formation (named from the Staffordshire locality of Huntley). They are all of Scythian age.[24][25]
Cumbria rock succession
[edit]On the Cumbrian coast the Group comprises the Calder Sandstone Formation and the underlying St Bees Sandstone Formation. The former is around 500m thick and includes sandstones of both aeolian and fluviatile origin. The latter is between 400 and 600m thick and includes some siltstone and claystone beds. It overlies the varied lithologies of the Permian age Cumbrian Coastal Group.[26] The Kirklinton Sandstone Formation in places overlies the Calder Sandstone Formation in the Carlisle and Vale of Eden basins of north and east Cumbria.[27] A sandstone which underlies Sellafield and Drigg is known as the Sellafield Member and is assigned to the Helsby Sandstone Formation.[28]
Southwest England rock succession
[edit]The group is represented in Somerset and east Devon by the Otterton Sandstone and the underlying Budleigh Salterton Pebble Beds formations,.[29]
References
[edit]- ^ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=SSG (BGS on-line lexicon of rock units)
- ^ Stuart, I. A.; Cowan, G. (1 January 1991), "The South Morecambe Field, Blocks 110/2a, 110/3a, 110/8a, UK East Irish Sea", Geological Society, London, Memoirs, 14: 527–541, doi:10.1144/GSL.MEM.1991.014.01.66, S2CID 140723122
- ^ "Oil and Gas from the Western Basins". United Kingdom Offshore Oil and Gas Industry Association. 2012. Archived from the original on 2013-06-28.
- ^ "Wytch Farm Oil Field - Hydrocarbons Technology". www.hydrocarbons-technology.com. Retrieved 2025-01-19.
- ^ British Geological Survey 1;50,000 scale geological map sheet (England and Wales series) no 28 Whitehaven
- ^ https://webapps.bgs.ac.uk/data/maps/maps.cfc?method=viewRecord&mapId=11211 (British Geological Survey 1:250 000 scale sheet East Irish Sea Special Sheet, Solid Geology.)
- ^ https://www.researchgate.net/publication/356617204_The_Permian_and_Mesozoic (The Geology of Ireland, Permian and Mesozoic)
- ^ British Geological Survey 1:625,000 scale Bedrock geology UK South & UK North sheets
- ^ https://webapps.bgs.ac.uk/memoirs/docs/B01565.html (Geology of the country around Buxton, Leek and Bakewell Memoir for 1:50 000 geological sheet 111 (England and Wales))
- ^ https://doi.org/10.1144/geoenergy2023-042 (Review of Triassic Sherwood Sandstone Group reservoirs of Ireland and Great Britain and their future role in geoenergy applications)
- ^ https://wessexcoastgeology.soton.ac.uk/Budleigh-Salterton.htm (Ian West. 2017. Budleigh Salterton, Littleham Cove, Devon and the Radioactive Nodules: Geology of the Wessex Coast)
- ^ https://wessexcoastgeology.soton.ac.uk/Sidmouth-Devon.htm (Ian West. 2017. Geology of Sidmouth and Ladram Bay, Devon, southern England. Jurassic Coast, UNESCO World Heritage Coast.)
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ a b British Geological Survey 1:50,000 scale geological map sheet (England and Wales series) 96 Liverpool
- ^ British Geological Survey 1:50,000 scale geological map sheets (England and Wales series) 97 Runcorn, 109 Chester and 122 Nantwich
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ British Geological Survey 1:50,000 scale geological map sheet (England and Wales series) 141 Loughborough
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ British Geological Survey 1:50,000 scale geological map sheet (England and Wales series) 155 Coalville
- ^ a b British Geological Survey 1:50,000 scale geological map sheet (England and Wales series) 123 Stoke-on-Trent
- ^ British Geological Survey 1:50,000 scale geological map sheets (England and Wales series) 124 Ashbourne
- ^ British Geological Survey 1:50,000 scale geological map sheet (England and Wales series) no 37 Gosforth
- ^ Stone P. et al 2010. British Regional Geology: Northern England (5th edn) Keyworth, Nottingham British Geological Survey ISBN 978-0-85272-652-5
- ^ "BGS Lexicon of Named Rocks Units". British Geological Survey. Retrieved 19 January 2019.
- ^ British Geological Survey 1:50,000 scale geological map (England) sheets 325, 326, 327 Exeter, Sidmouth & Bridport