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The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the Low Countries and the north of Germany. It consists of marine limestones, shales, marls and clays.
The Mercia Mudstone Group is an early Triassic lithostratigraphic group which is widespread in Britain, especially in the English Midlands – the name is derived from the ancient kingdom of Mercia which corresponds to that area. It is frequently encountered in older literature as the Keuper Marl or Keuper Marl Series.
The Drefach Group is an Ordovician lithostratigraphic group in west Wales. The name is derived from the village of Drefach near Meidrim in Carmarthenshire. The Group comprises the Mydrim Shales Formation, the Mydrim Limestone Formation, the Hendre Shales Formation, Asaphus Ash Formation and at its base, the underlying Felin-wen Formation.
The Mawddach Group is a middle to upper Cambrian lithostratigraphic group in Gwynedd, Wales. The name is derived from the river known as the Afon Mawddach.
The Sherwood Sandstone Group is a Triassic lithostratigraphic group 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. It has economic importance as the reservoir of the Morecambe Bay gas field, the second largest gas field in the UK.
The Cumbrian Coast Group is a Permian lithostratigraphic group which occurs in the western part of Cumbria in northern England.
The Aylesbeare Mudstone Group is an early Triassic lithostratigraphic group in southwest England. The name is derived from the village of Aylesbeare in east Devon. The Group comprises the Littleham Mudstone Formation, the Exmouth Mudstone and Sandstone Formation and the underlying Clyst St Lawrence Formation. The strata are exposed on the coast between Exmouth and Budleigh Salterton where the type section is defined. The rocks of the Aylesbeare Mudstone Group have also previously been known as the Aylesbeare Group and the Aylesbeare Mudstone Formation.
The Penarth Group is a Rhaetian age (Triassic) lithostratigraphic group which is widespread in Britain. It is named from the seaside town of Penarth near Cardiff in south Wales where strata of this age are exposed in coastal cliffs southwards to Lavernock Point. This sequence of rocks was previously known as the Rhaetic or Rhaetic Beds.
The geology of Lancashire in northwest England consists in the main of Carboniferous age rocks but with Triassic sandstones and mudstones at or near the surface of the lowlands bordering the Irish Sea though these are largely obscured by Quaternary deposits.
The Bacton Group is a Triassic lithostratigraphic group beneath the southern part of the North Sea. The name is derived from Bacton on the Norfolk coast. These strata, which are up to 600 m thick are the offshore equivalent of the Roxby Formation and Sherwood Sandstone Group which occur in northeast England. The group comprises a lower Bunter Shale Formation of red and brown to grey mudstones and an upper Bunter Sandstone Formation of dolomitic sandstones with mudstone interlayers.
The Heron Group is a Triassic lithostratigraphic group beneath the central and northern North Sea which is composed of alluvial deposits.
The Papa Group are a Triassic lithostratigraphic group beneath the seas northwest of Britain, and which originated as alluvial deposits. It is the lateral equivalent of the combined Mercia Mudstone and Sherwood Sandstone Groups in the Irish Sea and onshore Britain. It contains the Otter Bank Formation and the Foula Formation.
The Teign Valley Group is a late Devonian to late/middle Carboniferous lithostratigraphic group in north Cornwall through Devon and into west Somerset in southwest England. The name is derived from the valley of the River Teign. The Group comprises the Barras Nose, Trambley Cove, Teign Chert and Dowhills Mudstone formations. It also includes the Brendon and St Mellion formations whose stratigraphical context is unclear since all known boundaries of these two unit are tectonic. The Brendon Formation slates extend from Tavistock west to Bodmin Moor. The St Mellion Formation sandstones, siltsones and mudstones are found from Holne northeastwards. The Teign Valley Group was formerly known as the Lower Culm Group or Lower Culm Measures.
The Dunwich Group is a Pleistocene lithostratigraphic group present in England north of the upper Thames and, downstream, a line drawn east from near Marlow to Clacton-on-Sea and which encompasses river terrace deposits of the Proto-Thames and other rivers. It unconformably overlies Triassic to Pleistocene bedrock and superficial deposits. In turn, it is often overlain by deposits of the Albion Glacigenic Group and sometimes by those of the Britannia Catchments Group or British Coastal Deposits Group and interfingers in places with those of the Crag Group. No deposits potentially assignable to the group have been identified north of East Anglia or the English Midlands; they are likely to have been destroyed or removed by glacial action.
The Craven Group is a lithostratigraphical term referring to the succession of mudstone and limestone rock strata which occur in certain parts of northern and central England and northeast Wales in the United Kingdom within the Chadian to Yeadonian sub-Stages of the Carboniferous Period. Other lithologies including sandstones, siltstones and chert occur within the group. The Group is subdivided into numerous formations, some of which previously enjoyed group status. In stratigraphic order, these are:
The Riccarton Group is a Silurian lithostratigraphic group in southern Scotland and northern England. The name is derived from Riccarton in the Edinburgh area. The rocks of the Riccarton Group have also previously been known as the Riccarton Formation and the Riccarton and Raeberry Castle Beds. The Group comprises around 500m thickness of greywackes, mudstones and siltstones which are faulted and folded.
The Gala Group is a Silurian lithostratigraphic group in the Southern Uplands of Scotland and northernmost England. The name is derived from Gala Water, a tributary of the River Tweed. The rocks of the Gala Group have also previously been known as the Queensberry Grits and the Strangford Group. Graded beds variously of wackestone, siltstone and mudstone are interpreted as turbidites and have been matched with the Central Belt turbidites which are seen in the Ards Peninsula in Northern Ireland. The strata are generally near-vertical and are bounded to the north by the Orlock Bridge Fault and to the south by the Laurieston Fault. Graptolites are found in a few beds.
The Inverclyde Group is a Carboniferous lithostratigraphic group in southern Scotland and northernmost England. The name is derived from Inverclyde. The rocks of the Inverclyde Group have also previously been referred to as the Cementstone Group and Stirling Group. The group comprises sandstones with limestones and dolomites and some mudstone and lesser amounts of siltstone.
Fossil Beach, in Sedbury, Gloucestershire, is beneath the Sedbury Cliffs by the River Severn and is known as a rich source of easily discovered fossils. It is a Site of Special Scientific Interest (SSSI).
The Tyrone Group is a lithostratigraphical term coined to refer to a particular succession of rock strata which occur in Northern Ireland within the Visean Stage of the Carboniferous Period. It comprises a series of limestones, shales and sandstones which accumulated to a thickness of 2400m in the northwest Carboniferous basin of Ireland. The type areas for the group are the Clogher Valley of County Tyrone and the Fermanagh Highlands of nearby County Fermanagh. The rocks of the group sit unconformably on older rocks of the Shanmullagh Formation of the Fintona Group which are the local representatives of the Lower Old Red Sandstone. The top of the Dartry Limestone, the uppermost part of the group, is a disconformity, above which are the layered sandstones and shales of the Meenymore Formation of the Leitrim Group. The succession continues south and west across the border into the Republic of Ireland, though different names are typically applied.
References
- ↑ Johnson, H., Warrington, G. & Stoker, S. J. 1994. ‘’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’’. Nottingham: British Geological Survey.
- ↑ Rhys, G H, 1974. ‘’A proposed standard lithostratigraphic nomenclature for the southern North Sea and an outline structural nomenclature for the whole of the (UK) North Sea’’. Institute of Geological Sciences, Report No.74/8.
- ↑ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=HAI (BGS on-line lexicon of rock units)