Wem-Bridgemere-Red Rock Fault System
Encyclopedia
The Wem-Bridgemere-Red Rock Fault System is a complex zone of intersecting faults which defines the eastern boundary of the Cheshire Basin
, a deep sedimentary basin
in the northwest of England
and extending south into the northern Midlands
. It includes the Red Rock Fault, Bridgemere Fault and Wem Fault and reaches from Shropshire
through eastern Cheshire
to southeast Lancashire
.
At Norbury Brook, Poynton
, on the border of Cheshire and Greater Manchester
,the Millstone Grit
of the Pennines
makes a 200 metres (656.2 ft) downfall to be covered to the west by the glacial tills of the Cheshire Plain
formed by the retreating ice age
glaciers. To the east of the fault we have the Coal Measures
of the Carboniferous
period, which unlike those in the Lancashire Coalfield
are missing the top layers. Here we find outcrops of the Middle Coal Measures. Coal
from these strata, particularly the Four Foot mine (or seam), the Five Foot mine and the Accommodation mine was extract
ed in the nineteenth and early twentieth century.
The two masses are still moving and regularly generate small earthquake
s usually less than 3.0 on the Richter Scale along its length. In 2002 there was a swarm of 100 earthquakes felt in Manchester, close to the fault, over a period of a few days. The strongest was 3.9, on Thursday, 24 October 2002 at 08:25 GMT.
Cheshire Basin
The Cheshire Basin is a late Palaeozoic and Mesozoic sedimentary basin which extends under most of the county of Cheshire in northwest England. It extends northwards into the Manchester area and south into Shropshire...
, a deep sedimentary basin
Sedimentary basin
The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification...
in the northwest of England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
and extending south into the northern Midlands
English Midlands
The Midlands, or the English Midlands, is the traditional name for the area comprising central England that broadly corresponds to the early medieval Kingdom of Mercia. It borders Southern England, Northern England, East Anglia and Wales. Its largest city is Birmingham, and it was an important...
. It includes the Red Rock Fault, Bridgemere Fault and Wem Fault and reaches from Shropshire
Shropshire
Shropshire is a county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. It borders Wales to the west...
through eastern Cheshire
Cheshire
Cheshire is a ceremonial county in North West England. Cheshire's county town is the city of Chester, although its largest town is Warrington. Other major towns include Widnes, Congleton, Crewe, Ellesmere Port, Runcorn, Macclesfield, Winsford, Northwich, and Wilmslow...
to southeast Lancashire
Lancashire
Lancashire is a non-metropolitan county of historic origin in the North West of England. It takes its name from the city of Lancaster, and is sometimes known as the County of Lancaster. Although Lancaster is still considered to be the county town, Lancashire County Council is based in Preston...
.
At Norbury Brook, Poynton
Poynton
Poynton is a town within the civil parish of Poynton-with-Worth, and the unitary authority area of Cheshire East, England. For ceremonial purposes it is part of the county of Cheshire. Poynton is located at the eastern most fringe of the Cheshire Plain, north of Macclesfield, south of Stockport...
, on the border of Cheshire and Greater Manchester
Greater Manchester
Greater Manchester is a metropolitan county in North West England, with a population of 2.6 million. It encompasses one of the largest metropolitan areas in the United Kingdom and comprises ten metropolitan boroughs: Bolton, Bury, Oldham, Rochdale, Stockport, Tameside, Trafford, Wigan, and the...
,the Millstone Grit
Millstone Grit
Millstone Grit is the name given to any of a number of coarse-grained sandstones of Carboniferous age which occur in the Northern England. The name derives from its use in earlier times as a source of millstones for use principally in watermills...
of the Pennines
Pennines
The Pennines are a low-rising mountain range, separating the North West of England from Yorkshire and the North East.Often described as the "backbone of England", they form a more-or-less continuous range stretching from the Peak District in Derbyshire, around the northern and eastern edges of...
makes a 200 metres (656.2 ft) downfall to be covered to the west by the glacial tills of the Cheshire Plain
Cheshire Plain
The Cheshire Plain is a relatively flat expanse of lowland situated almost entirely within the county of Cheshire in northwest England. It is bounded by the hills of North Wales to the west, and the Peak District of Derbyshire and North Staffordshire to the east and southeast...
formed by the retreating ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
glaciers. To the east of the fault we have the Coal Measures
Coal Measures
The Coal Measures is a lithostratigraphical term for the coal-bearing part of the Upper Carboniferous System. It represents the remains of fluvio-deltaic sediment, and consists mainly of clastic rocks interstratified with the beds of coal...
of the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
period, which unlike those in the Lancashire Coalfield
Lancashire Coalfield
The Lancashire Coalfield in north-west England was one of the most important British coalfields.-Geography and geology:The geology of the coalfield consists of the coal seams of the Upper, Middle and Lower Coal Measures, layers of sandstones, shales and coal of varying thickness, which were laid...
are missing the top layers. Here we find outcrops of the Middle Coal Measures. Coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
from these strata, particularly the Four Foot mine (or seam), the Five Foot mine and the Accommodation mine was extract
Coal mining
The goal of coal mining is to obtain coal from the ground. Coal is valued for its energy content, and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production. In the United States,...
ed in the nineteenth and early twentieth century.
The two masses are still moving and regularly generate small earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s usually less than 3.0 on the Richter Scale along its length. In 2002 there was a swarm of 100 earthquakes felt in Manchester, close to the fault, over a period of a few days. The strongest was 3.9, on Thursday, 24 October 2002 at 08:25 GMT.