Coal measures

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British coalfields in the 19th century British.coalfields.19th.century.jpg
British coalfields in the 19th century

In lithostratigraphy, coal measures are coal-bearing strata, with the term typically applied to European units of the Upper Carboniferous System.

Contents

In the United Kingdom, the term is equivalent to regional components of the Westphalian-age Coal Measures Group. The group records the deposition of fluvio-deltaic sediments which consists mainly of clastic rocks (claystones, shales, siltstones, sandstones, conglomerates) interstratified with the beds of coal. In most places, the coal measures are underlain by coarser clastic sequences known as Millstone Grit, of Namurian age. The top of the coal measures may be marked by an unconformity, the overlying rocks being Permian or later in age. In some parts of Britain, however, the coal measures grade up into mainly coal-barren red beds of late Westphalian and possibly Stephanian age. [1] [2] Within the Pennine Basin, these barren measures are now referred to as the Warwickshire Group, from the district where they achieve their thickest development. [3]

The coal measures formed during Westphalian and earliest Stephanian times in the European ('Heerlen') chronostratigraphical scheme (which is approximately equivalent to the Middle Pennsylvanian Series of the IUGS global chronostratigraphical scheme).

Informal usage for other coal-bearing strata

In the eastern United States the term coal measures has been applied to the Pennsylvanian coal fields. Generally, the Pittsburgh coal seam is considered the base of the upper coal measures, exposed along the Monongahela River, while the lower coal measures are exposed along the Allegheny River. [4]

The term coal measures has also historically been used in other parts of the world for coal-bearing successions of various ages, e.g. the Permian coal measures of Australia and the late Cretaceous and early Tertiary coal measures found in New Zealand. However, these usages are mostly informal.

See also

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The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly 323.2 million years ago to 298.9 million years ago. As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few hundred thousand years. The Pennsylvanian is named after the U.S. state of Pennsylvania, where the coal-producing beds of this age are widespread.

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Seatearth is a British coal mining term, which is used in the geological literature. As noted by Jackson, a seatearth is the layer of sedimentary rock underlying a coal seam. Seatearths have also been called seat earth, "seat rock", or "seat stone" in the geologic literature. Depending on its physical characteristics, a number of different names, such as underclay, fireclay, flint clay, and ganister can be applied to a specific seatearth.

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The geology of Cheshire in England consists mainly of Triassic sandstones and mudstones. To the north west of Cheshire, these rocks are heavily faulted and the underlying Carboniferous Coal Measures are thrown up. Around the areas of Poynton and Macclesfield, the coal is close to the surface and was easily mined. Below the Coal Measures is the Millstone Grit, which appears towards the Derbyshire border on the flanks of the Peak District dome.

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The Namurian is a stage in the regional stratigraphy of northwest Europe, with an age between roughly 331 and 319 Ma. It is a subdivision of the Carboniferous system or period, as well as the regional Silesian series. The Namurian is named for the Belgian city and province of Namur where strata of this age occur. The Millstone Grit Group in the lithostratigraphy of northern England and parts of Wales is also of Namurian age.

<span class="mw-page-title-main">Pennant Measures</span> Geological term for rock in south Wales

The Pennant Measures is the traditional name for a sequence of sedimentary rocks of the South Wales Coalfield. They were also referred to as the Upper Coal Measures and assigned to the Westphalian 'C' and Westphalian 'D' stages of the Carboniferous Period. The Pennant Measures were divided into the Lower Pennant Measures and the Upper Pennant Measures, differing from the underlying Middle and Lower Coal Measures in being principally of sandstone units – known collectively as the Pennant Sandstone – with mudstone being the subsidiary rock type. Numerous coal seams occur within the Pennant Measures though they are less common than in the underlying Coal Measures.

The Westphalian is a stage or age in the regional stratigraphy of northwest Europe, with an age between roughly 319 and 307.5 Ma. It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Westphalian is named for the region of Westphalia in western Germany where strata of this age occur. The Coal Measures of England and Wales are also largely of Westphalian age, though they also extend into the succeeding Stephanian.

The Stephanian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 307.5 and 299 Ma. It is a subdivision of the Carboniferous system or period and the regional Silesian series. The uppermost units of the Coal Measures of England and Wales are probably of Stephanian age, though the larger part of this formation is referred to the earlier Westphalian. The stage derives its name from the city of Saint-Étienne for its coal mining basin in eastern central France where strata of this age occur.

The Warwickshire Group is a lithostratigraphic unit of rock strata defined within the British Carboniferous system. Within the Pennine Basin it overlies the Coal Measures Group and is deemed to be of late Westphalian and Stephanian age. In the South Wales Coalfield it consists of the Pennant Sandstone Formation and overlying Grovesend Formation. It contains the youngest Carboniferous rocks in Britain. The name Warwickshire Group is a relatively recent one, replacing a variety of earlier names for the succession of coal-barren red-beds such as Barren Coal Measures and Red Measures which overlie the productive coal measures. It is derived from the Warwickshire Coalfield where they achieve their thickest development.

The Coal Measures Group is a lithostratigraphical term coined to refer to the coal-bearing succession of rock strata which occur in the United Kingdom within the Westphalian Stage of the Carboniferous Period. The succession was previously referred to as the 'Productive Coal Measures'. Other than in Northern Ireland the term is now obsolete in formal use and is replaced by the Pennine Coal Measures Group, Scottish Coal Measures Group and the South Wales Coal Measures Group for the three distinct depositional provinces of the British mainland.

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 geology of Merseyside in northwest England largely consists of a faulted sequence of Carboniferous Coal Measures rocks overlain in the west by younger Triassic and Permian age sandstones and mudstones. Glaciation during the present Quaternary Period has left widespread glacial till as well as erosional landforms. Other post-glacial superficial deposits such as river and estuarine alluvium, peat and blown sand are abundant.

The Pennine Coal Measures Group is a lithostratigraphical term referring to the coal-bearing succession of rock strata which occur in the United Kingdom within the Westphalian Stage of the Carboniferous Period. In formal use, the term replaces the Coal Measures Group as applied to the succession of coal-bearing strata within the Pennine Basin which includes all of the coalfields of northern England and the English Midlands. It includes the largely concealed Canonbie Coalfield of southern Scotland and the coalfields of northeast Wales and the minor Anglesey coalfield.

The geology of County Durham in northeast England consists of a basement of Lower Palaeozoic rocks overlain by a varying thickness of Carboniferous and Permo-Triassic sedimentary rocks which dip generally eastwards towards the North Sea. These have been intruded by a pluton, sills and dykes at various times from the Devonian Period to the Palaeogene. The whole is overlain by a suite of unconsolidated deposits of Quaternary age arising from glaciation and from other processes operating during the post-glacial period to the present. The geological interest of the west of the county was recognised by the designation in 2003 of the North Pennines Area of Outstanding Natural Beauty as a European Geopark.

The South Wales Coal Measures Group is a lithostratigraphical term referring to the coal-bearing succession of rock strata which occur in South Wales within the Westphalian Stage of the Carboniferous Period. The Group name is also applied to rocks of similar age across southern England from the Bristol Coalfield east to the concealed Oxfordshire, Berkshire and Kent Coalfields. In formal use, the term replaces the earlier Coal Measures Group The Group comprises the:

The geology of the Yorkshire Dales National Park in northern England largely consists of a sequence of sedimentary rocks of Ordovician to Permian age. The core area of the Yorkshire Dales is formed from a layer-cake of limestones, sandstones and mudstones laid down during the Carboniferous period. It is noted for its karst landscape which includes extensive areas of limestone pavement and large numbers of caves including Britain's longest cave network.

The Scottish Coal Measures Group is a lithostratigraphic unit referring to the coal-bearing succession of rock strata which occur in Scotland during the Westphalian regional stage of the Carboniferous Period. It is the Scottish portion of the informal Coal Measures Group, which also includes the South Wales and Pennine coal measures. The Scottish coal measures are well-exposed across the Midland Valley. The group is also found within small grabens in the vicinity of Sanquhar and Thornhill.

References

  1. Rayner, D H; Hemingway, J E (1974), The Geology and Mineral Resources Of Yorkshire, Leeds: Yorkshire Geological Society
  2. Edwards, W; Trotter, F M (1954), The Pennines and Adjacent Areas, British Regional Geology (Third ed.), London: HMSO. Natural Environment Research Council
  3. Powell, J.; Chisholm, J.; Bridge, D.; Rees, J.; Glover, B.W.; Besly, B.M. (2000). "Stratigraphical framework for Westphalian to Early Permian red-bed successions of the Pennine Basin" (PDF). British Geological Survey Research Report. RR/00/01. Retrieved 13 November 2021.
  4. Stratigraphy of the Bituminous Coal Field in Pennsylvania, Ohio and West Virginia, Bulletin of the United States Geological Survey No. 65, Washington, Government Printing Office, 1891. See Chapter III and V.

Further reading