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.
A small fault-bounded area of rocks of Wenlock age lies to the north of Ireby in the extreme north of the county.
Rocks originating in the Carboniferous Period underlie the uplands of eastern and north Lancashire. Listed in order of succession i.e. lowermost/oldest first, they comprise the various limestones, mudstones, siltstones and sandstones of the Bowland High Group and Trawden Limestone Group, Craven Group, Millstone Grit Group, Pennine Coal Measures Group and Warwickshire Group.
The Bowland High Group is bundled together with the Trawden Limestone Group in the Carboniferous Limestone Supergroup. Together they include sedimentary sequences developed during the Tournaisian on isolated structural highs or horsts, namely the Bowland High and the Central Lancashire High. The Bowland High Group comprises the older Chatburn Limestone Formation and the younger Clitheroe Limestone Formation. These are largely limestone sequences but with subordinate mudstones and siltstones. The Trawden Limestone Group is not known at the surface but is proved in numerous boreholes. It is not divided into formations. [1]
The overlying Craven Group comprises, again in stratigraphic order, the Hodder Mudstone, Hodderense Limestone, Pendleside Limestone and Bowland Shale Formations. These are of Visean and earliest Namurian age. Older texts refer instead to a Worston Shale Group comprising the first three of the above formations (and including the Clitheroe Limestone Formation), and an overlying Bowland Shale Group comprising a Lower and an Upper Bowland Shale.
The Millstone Grit Group comprises the Pendleton, Silsden, Samlesbury, Hebden, Marsden and Rossendale formations. This succession of sandstones and mudstones was deposited during Namurian times. The sandstones of the Rossendale Formation have been widely quarried for building purposes; Rossendale Flags are found as paving widely across the region. Older texts subdivide the Millstone Grit in different ways.
The sandstones, mudstones and coals of the Pennine Coal Measures Group form the Lancashire Coalfield which includes both the Burnley Coalfield and the South Lancashire Coalfield. Both were economically important to Lancashire's economy during the nineteenth and twentieth centuries. The Group is divided into Lower, Middle and Upper formations, all dating from the Westphalian. These are in turn overlain by the Etruria and Halesowen formations of the Warwickshire Group. [2]
Longridge Fell is formed in the Pendle Grit. Strata dip locally to the south and south-east presenting a prominent northwest-facing scarp. Pendle Hill is similarly formed from these erosion-resistant sandstones. The southern part of the Forest of Bowland, including the prominent Parlick together with the isolated Beacon Fell are also formed from the Pendle Grit. The Ward's Stone Sandstone Formation forms the western parts of these fells whilst to the north-east it is the Dure Clough Sandstone which forms the plateau surface.
The Arnside and Silverdale AONB, the southern half of which is within Lancashire is formed by a succession of limestones assigned to the Great Scar Limestone Group. Warton Crag and Jack Scout, a National Trust property, are prominent features in the locality where the limestone is well exposed.
Leck Fell is an area of limestone moorland west of the hill of Gragareth, the county's highest point, close to the border with both North Yorkshire and Cumbria. A succession of limestones assigned to the Great Scar Limestone Group and Yoredale Group are host to numerous cave systems. The summit area is formed in rocks of the Alston and Pendleton formations.
Billinge Hill, Blackburn near Blackburn is formed by the Revidge Grit whilst the nearby Hoghton Tower stands on a lower hill formed by the same Namurian age rock, one of a series of sandstones within the Millstone Grit. Anglezarke Moor and Withnell Moor are formed by the Fletcher Bank, Helmshore and Brooksbottoms grits. [3]
The fells to the south of Slaidburn, including Easington, Waddington and Birkett fells are formed from the Warley Wise Grit. It was formerly quarried beside the B6478 road in this vicinity. [4]
A small area of rocks originating in the Permian Period occurs near Lancaster, Morecambe and Glasson Dock though it is entirely obscured by recent deposits and is known only from borehole cores. These are the Collyhurst Sandstone of the Appleby Group and the sandstones, mudstones and evaporites of the overlying Cumbrian Coast Group. There are also narrow bands of these rocks (Manchester Marls and Collyhurst Sandstone) to the north and south of Preston though again they are generally buried beneath glacial till. Another small outlier of early/lower Permian rocks is centred on the village of Ireby and extends across the county boundary into North Yorkshire.
Lancashire's coastal plain is underlain by sedimentary rocks laid down during the Triassic Period comprising sandstones, siltstones and mudstones though outcrops are restricted to those areas which are not covered by thick superficial deposits. Within the Kirkham basin, the following Triassic sequence is known from boreholes:
The lowermost part of the Sherwood Sandstone Group is of Permian age. The two groups as currently defined replace earlier terminology which referred to the Bunter Sandstone, Keuper Sandstone and Keuper Marl. [5] A small outlier of Sherwood Sandstone Group rocks occurs at the surface at Skelmersdale.
The Preesall Salt occurs within the Kirkham Mudstones in a syncline beneath Preesall and the River Wyre. At least 185m thickness of halite with some mudstone is known to exist. There is also some salt present in the overlying Breckells Mudstones. [6]
Caton Dyke, a dyke of olivine alkali basalt intrudes Carboniferous strata east of Caton. Its alignment is roughly similar to that of numerous faults in the area and is seen to vary in width from over 5m to just 60 cm across its three known exposures. It is considered that it may form a part of the dyke swarm associated with the Isle of Mull off the west coast of Scotland. It is thought to be continuous with Grindleton Dyke in the Clitheroe area. [7]
Much of the county occupies the Craven Basin, a depositional basin active during the Carboniferous period. It is bounded to the north by the Lake District block and to the southeast by the Central Lancashire High. To the northeast the Craven Fault System marks the edge of the Askrigg Block. Within the basin a couple of sub-basins are recognised; the Lancaster Fells sub-basin and Bowland sub-basin (or 'Bowland Trough'), separated by the 'Bowland High' and 'South Fells Tilt Block'. Rocks in the area, especially within the latter sub-basin were folded during the Variscan Orogeny to form the Ribblesdale Fold Belt which is aligned broadly southwest - northeast. Further south is the Rossendale Basin. [8]
In the west of the county, the West Lancashire basin is in effect a landward extension of the East Irish Sea Basin. The area is threaded by numerous broadly north-south aligned normal faults thought to have been active during Permo-Triassic times and perhaps later, in association with early rifting of the Atlantic Ocean. [9]
The larger part of lowland Lancashire i.e. the West Lancashire Coastal Plain, The Fylde and adjoining areas is covered by a thick mantle of glacial till. These deposits are the legacy of the over-riding of the area on several occasions by glacial ice during the past 2 million years. The present distribution of deposits and the landforms to which they give rise are largely the result of the last ice age, the Devensian which peaked around 22-20,000 years ago. Drumlins caused by the moulding of sub-glacial sediments are a significant feature of the landscape in the north of the county.
Significant areas of marine and estuarine alluvium, typically silt and clay, extend around Ribble estuary north from Southport and also around the southern shores of Morecambe Bay from Cleveleys and Fleetwood east through Preesall then north via Glasson to Morecambe. Narrower bands of these deposits fringe the coast between Hest Bank and Carnforth. River alluvium is characteristic of the floodplains of the River Wyre and its major tributary, the River Brock. [10]
Extensive areas of blown sand have been mapped along the coastal zone south from Blackpool through Lytham St Annes. Narrower belts of these deposits also characterise the north coast of Fylde at Fleetwood and Preesall and a rather smaller area west of Sunderland Point. Considerable areas in the south of the county around Ormskirk are characterised by blown sand, referred to here as the Shirdley Hill Sand. After the ice sheets had melted away from the Irish Sea but before vegetation had taken hold and before the sea re-flooded that basin, blowing sand drifted across the area to form a sheetlike deposit up to 2.5m thick in places. [11]
Peat deposits are common in the county and can be divided into areas of 'lowland moss' and 'hill peat'. Large swathes of the Forest of Bowland are covered in peat and there are smaller patches elsewhere as at Pendle Hill. Lowland examples include Stalmine Moss, Rawcliffe Moss, Winmarleigh and Cockerham mosses west of Garstang. There is also a large area east of Southport where extensive raised bogs have been drained. Many have been thoroughly exploited. [12]
There has been development of cave systems in parts of the county where limestone is present. Of particular note is the Three Counties System which, besides Lancashire, underlies neighbouring parts of North Yorkshire and Cumbria. At over 86 km in length it is the most extensive cave network known in Britain and ranks 27th longest in the world. [13] Various individually named caves beneath Leck Fell link underground to form the wider system. These include Ease Gill Caverns, Lost John's Cave and Ireby Fell Cavern.
Numerous examples of landslides occur around the east of the county. A study in the Forest of Rossendale by the British Geological Survey revealed three main types of occurrence, namely those associated with:
They range from rotational ones, often multiple in nature to simple topples and rock falls. The Cliviger valley is particularly affected by landslips which have occurred in the post-glacial period. [14]
The geology of the county of Shropshire, England is very diverse with a large number of periods being represented at outcrop. The bedrock consists principally of sedimentary rocks of Palaeozoic and Mesozoic age, surrounding restricted areas of Precambrian metasedimentary and metavolcanic rocks. The county hosts in its Quaternary deposits and landforms, a significant record of recent glaciation. The exploitation of the Coal Measures and other Carboniferous age strata in the Ironbridge area made it one of the birthplaces of the Industrial Revolution. There is also a large amount of mineral wealth in the county, including lead and baryte. Quarrying is still active, with limestone for cement manufacture and concrete aggregate, sandstone, greywacke and dolerite for road aggregate, and sand and gravel for aggregate and drainage filters. Groundwater is an equally important economic resource.
Millstone Grit is any of a number of coarse-grained sandstones of Carboniferous age which occur in the British Isles. The name derives from its use in earlier times as a source of millstones for use principally in watermills. Geologists refer to the whole suite of rocks that encompass the individual limestone beds and the intervening mudstones as the Millstone Grit Group. The term Millstone Grit Series was formerly used to refer to the rocks now included within the Millstone Grit Group together with the underlying Edale Shale Group.
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.
The Geology of Yorkshire in northern England shows a very close relationship between the major topographical areas and the geological period in which their rocks were formed. The rocks of the Pennine chain of hills in the west are of Carboniferous origin whilst those of the central vale are Permo-Triassic. The North York Moors in the north-east of the county are Jurassic in age while the Yorkshire Wolds to the south east are Cretaceous chalk uplands. The plain of Holderness and the Humberhead levels both owe their present form to the Quaternary ice ages. The strata become gradually younger from west to east.
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 geology of Monmouthshire in southeast Wales largely consists of a thick series of sedimentary rocks of different types originating in the Silurian, Devonian, Carboniferous, Triassic and Jurassic periods.
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 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 geology of Tyne and Wear in northeast England largely consists of a suite of sedimentary rocks dating from the Carboniferous and Permian periods into which were intruded igneous dykes during the later Palaeogene Period.
The geology of West Sussex in southeast England comprises a succession of sedimentary rocks of Cretaceous age overlain in the south by sediments of Palaeogene age. The sequence of strata from both periods consists of a variety of sandstones, mudstones, siltstones and limestones. These sediments were deposited within the Hampshire and Weald basins. Erosion subsequent to large scale but gentle folding associated with the Alpine Orogeny has resulted in the present outcrop pattern across the county, dominated by the north facing chalk scarp of the South Downs. The bedrock is overlain by a suite of Quaternary deposits of varied origin. Parts of both the bedrock and these superficial deposits have been worked for a variety of minerals for use in construction, industry and agriculture.
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 geology of Northumberland in northeast England includes a mix of sedimentary, intrusive and extrusive igneous rocks from the Palaeozoic and Cenozoic eras. Devonian age volcanic rocks and a granite pluton form the Cheviot massif. The geology of the rest of the county is characterised largely by a thick sequence of sedimentary rocks of Carboniferous age. These are intruded by both Permian and Palaeogene dykes and sills and the whole is overlain by unconsolidated sediments from the last ice age and the post-glacial period. The Whin Sill makes a significant impact on Northumberland's character and the former working of the Northumberland Coalfield significantly influenced the development of the county's economy. The county's geology contributes to a series of significant landscape features around which the Northumberland National Park was designated.
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.
The geology of Exmoor National Park in south-west England contributes significantly to the character of Exmoor, a landscape which was designated as a national park in 1954. The bedrock of the area consists almost wholly of a suite of sedimentary rocks deposited during the Devonian, a period named for the English county of Devon in which the western half of the park sits. The eastern part lies within Somerset and it is within this part of the park that limited outcrops of Triassic and Jurassic age rocks are to be found.
This article describes the geology of the Brecon Beacons National Park in mid/south Wales. The area gained national park status in 1957 with the designated area of 1,344 km2 (519 sq mi) including mountain massifs to both the east and west of the Brecon Beacons proper. The geology of the national park consists of a thick succession of sedimentary rocks laid down from the late Ordovician through the Silurian and Devonian to the late Carboniferous period. The rock sequence most closely associated with the park is the Old Red Sandstone from which most of its mountains are formed. The older parts of the succession, in the northwest, were folded and faulted during the Caledonian orogeny. Further faulting and folding, particularly in the south of the park is associated with the Variscan orogeny.
The geology of Northumberland National Park in northeast England includes a mix of sedimentary, intrusive and extrusive igneous rocks from the Palaeozoic and Cenozoic eras. Devonian age volcanic rocks and a granite pluton form the Cheviot massif. The geology of the rest of the national park is characterised largely by a thick sequence of sedimentary rocks of Carboniferous age. These are intruded by Permian dykes and sills, of which the Whin Sill makes a significant impact in the south of the park. Further dykes were intruded during the Palaeogene period. The whole is overlain by unconsolidated sediments from the last ice age and the post-glacial period.
The geology of the Gower Peninsula in South Wales is central to the area's character and to its appeal to visitors. The peninsula is formed almost entirely from a faulted and folded sequence of Carboniferous rocks though both the earlier Old Red Sandstone and later New Red Sandstone are also present. Gower lay on the southern margin of the last ice sheet and has been a focus of interest for researchers and students in that respect too. Cave development and the use of some for early human occupation is a further significant aspect of the peninsula's scientific and cultural interest.
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 geology of the Peak District National Park in England is dominated by a thick succession of faulted and folded sedimentary rocks of Carboniferous age. The Peak District is often divided into a southerly White Peak where Carboniferous Limestone outcrops and a northerly Dark Peak where the overlying succession of sandstones and mudstones dominate the landscape. The scarp and dip slope landscape which characterises the Dark Peak also extends along the eastern and western margins of the park. Although older rocks are present at depth, the oldest rocks which are to be found at the surface in the national park are dolomitic limestones of the Woo Dale Limestone Formation seen where Woo Dale enters Wye Dale east of Buxton.
The geology of Staffordshire in the West Midlands region of England is largely characterised by sedimentary bedrock of late Palaeozoic to early Mesozoic age overlain by a suite of superficial materials deposited during the Quaternary period. The extraction of coal, limestone and clay have been significant industries within the county.
{{cite web}}
: CS1 maint: unfit URL (link)