Editing Carboniferous of the Wear Valley and Derwent Gorge, County Durham - an excursion

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The Carboniferous rocks of County Durham '''dip''' eastwards off the northern Pennines so that the Lower Carboniferous (Dinantian) crops out in the west followed by successively higher Namurian and Westphalian (Coal Measures) strata towards the east. Permian sediments overlie the Coal Measures in east Durham. Bedrock is masked by thick glacial '''drift''' in the eastern part of the county and natural exposures of the Coal Measures are relatively few and incomplete. Further west, the Namurian sequence forms the tops of the fells in west Durham and here almost continuous blanket bog limits the exposures of bedrock. The Dinantian crops out in the valleys of the Pennines where it can be seen in river and stream sections. Thick and continuous Dinantian limestone successions in southern England and the Midlands change northwards into sequences of limestone, shale and sandstone in northern England as the Carboniferous shoreline is approached. The most northerly of the thick Asbian limestones, the Melmerby Scar Limestone, becomes divided by elastic sediment and looses its identity in Durham. Clastic sediment increases in the overlying Brigantian where cyclic deposition of limestone, shale and sandstone is repeated ten times. This '''Yoredale''' facies is remarkably persistent over northern England from the Scottish Border southwards to the Craven '''faults'''. The sequence is controlled to an extent by the position of the Carboniferous shoreline. Marine limestones and shales increase in thickness seawards towards the south and west and thin and die out towards the shore to the north and east. Similarly, the deltaic and subaerial sandstones and coal seams thicken landwards and thin seawards. Durham lies almost midway across the broad area in which open sea and shoreline environments alternated and well developed '''cyclothems''' of marine and deltaic sediment are developed. A section of Yoredale cycles in Middlehope Burn is described at Locality 1.
 
The Carboniferous rocks of County Durham '''dip''' eastwards off the northern Pennines so that the Lower Carboniferous (Dinantian) crops out in the west followed by successively higher Namurian and Westphalian (Coal Measures) strata towards the east. Permian sediments overlie the Coal Measures in east Durham. Bedrock is masked by thick glacial '''drift''' in the eastern part of the county and natural exposures of the Coal Measures are relatively few and incomplete. Further west, the Namurian sequence forms the tops of the fells in west Durham and here almost continuous blanket bog limits the exposures of bedrock. The Dinantian crops out in the valleys of the Pennines where it can be seen in river and stream sections. Thick and continuous Dinantian limestone successions in southern England and the Midlands change northwards into sequences of limestone, shale and sandstone in northern England as the Carboniferous shoreline is approached. The most northerly of the thick Asbian limestones, the Melmerby Scar Limestone, becomes divided by elastic sediment and looses its identity in Durham. Clastic sediment increases in the overlying Brigantian where cyclic deposition of limestone, shale and sandstone is repeated ten times. This '''Yoredale''' facies is remarkably persistent over northern England from the Scottish Border southwards to the Craven '''faults'''. The sequence is controlled to an extent by the position of the Carboniferous shoreline. Marine limestones and shales increase in thickness seawards towards the south and west and thin and die out towards the shore to the north and east. Similarly, the deltaic and subaerial sandstones and coal seams thicken landwards and thin seawards. Durham lies almost midway across the broad area in which open sea and shoreline environments alternated and well developed '''cyclothems''' of marine and deltaic sediment are developed. A section of Yoredale cycles in Middlehope Burn is described at Locality 1.
  
The Great Limestone (22 m) is the thickest limestone in the Yoredale succession. It contains fossil '''biostromes''' including the Frosterley Marble, a band rich in solitary rugose '''corals''' (Locality 2). Index fossils collected from above and below the limestone indicate that the base lies near to the Dinantian/Namurian boundary. The Great Limestone cycle continues the Yoredale facies into the Namurian, but above this the limestone bands become thinner in a dominantly shale and sandstone succession. Towards the top of the Namurian thick, coarse-grained sandstones are widely developed. The upper part of the Namurian including the First and Second Grits can be seen at Locality 3.
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The Great Limestone (22 m) is the thickest limestone in the Yoredale succession. It contains fossil '''biostromes''' including the Frosterley Marble, a band rich in solitary rugose '''corals''' (Locality 2). Index fossils collected from above and below the limestone indicate that the base lies near to the Dinantian/Namurian boundary. The Great Limestone cycle continues the Yoredale facies into the Namurian, but above this the limestone bands become thinner in a dominantly shale and sandstone succession. Towards the top of the Namurian thick, coarse-grained sandstones are widely developed. The upper part of the Namurian including the First and Second Grits can be seen at Locality 3.
  
 
In Durham the base of the Westphalian is believed to be at the level of the Quarterburn Marine Band. The upper Namurian coarse-grained sandstone facies continues into the Westphalian and rapidly gives way to a delta-top sequence of sandstone and shale with coal seams. These deposits, formed mainly in lakes and interdistributary bays, contain twenty major exploitable coal seams that formed the celebrated Northumberland and Durham coalfield. A Westphalian B succession can be seen at Locality 4.
 
In Durham the base of the Westphalian is believed to be at the level of the Quarterburn Marine Band. The upper Namurian coarse-grained sandstone facies continues into the Westphalian and rapidly gives way to a delta-top sequence of sandstone and shale with coal seams. These deposits, formed mainly in lakes and interdistributary bays, contain twenty major exploitable coal seams that formed the celebrated Northumberland and Durham coalfield. A Westphalian B succession can be seen at Locality 4.

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