Editing Upper Carboniferous of the Halifax area - an excursion

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=== Locality 1, Clockface Quarry [SE 046 175] ===
 
=== Locality 1, Clockface Quarry [SE 046 175] ===
  
The quarry is situated next to the B6114 Rochdale Road between Ringstone Edge Reservoir and the M62 Motorway and illustrates a distributary channel sandbody and interdistributary bay-fill deposits. This is a working quarry and prior permission is required for visits. The quarry provides good, two-dimensional exposures of the Namurian Midgley Grit ([[:File:YGS_YORKROCK_FIG_09_02.jpg|Figure 9.2]]a), located between the Bilinguites bilinguis Marine Band and the Bilinguites metabilinguis Marine Band in the middle of the Marsdenian (R2) Stage ([[:File:YGS_YORKROCK_FIG_09_01.jpg|Figure 9.1]]). The base of the quarry face consists of about 2  of incompletely exposed, burrowed and '''bioturbated''', plant-rich, fine micaceous sandstone and siltstone containing locally rippled sandy intervals. These are sharply overlain by trough '''cross-stratified''', coarse to very coarse, granular and pebbly sandstone containing abundant carbonaceous plant material, commonly concentrated on '''foresets''' and the base of troughs ([[:File:YGS_YORKROCK_FIG_09_03.jpg|Figure 9.3]]). Softish weathered, brown, iron-rich nodules and lenses occur at intervals in the sandstone. The northern end of the quarry, which has been locally affected by a northwest–southeast trending fault, reveals the presence of large-scale cross-strata '''dipping''' in opposite directions with individual foresets internally structured by trough cross-stratification, plane lamination and low angle lamination ([[:File:YGS_YORKROCK_FIG_09_02.jpg|Figure 9.2]]a). These are interpreted as mid-channel or bank-attached sand bars within a major distributary channel, scoured into the abandonment, or bay-fill deposits beneath.
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The quarry is situated next to the B6114 Rochdale Road between Ringstone Edge Reservoir and the M62 Motorway and illustrates a distributary channel sandbody and interdistributary bay-fill deposits. This is a working quarry and prior permission is required for visits. The quarry provides good, two-dimensional exposures of the Namurian Midgley Grit ([[:File:YGS_YORKROCK_FIG_09_02.jpg|Figure 9.2]]a), located between the Bilinguites bilinguis Marine Band and the Bilinguites metabilinguis Marine Band in the middle of the Marsdenian (R2) Stage ([[:File:YGS_YORKROCK_FIG_09_01.jpg|Figure 9.1]]). The base of the quarry face consists of about 2 m of incompletely exposed, burrowed and bioturbated, plant-rich, fine micaceous sandstone and siltstone containing locally rippled sandy intervals. These are sharply overlain by trough cross-stratified, coarse to very coarse, granular and pebbly sandstone containing abundant carbonaceous plant material, commonly concentrated on foresets and the base of troughs ([[:File:YGS_YORKROCK_FIG_09_03.jpg|Figure 9.3]]). Softish weathered, brown, iron-rich nodules and lenses occur at intervals in the sandstone. The northern end of the quarry, which has been locally affected by a northwest–southeast trending fault, reveals the presence of large-scale cross-strata dipping in opposite directions with individual foresets internally structured by trough cross-stratification, plane lamination and low angle lamination ([[:File:YGS_YORKROCK_FIG_09_02.jpg|Figure 9.2]]a). These are interpreted as mid-channel or bank-attached sand bars within a major distributary channel, scoured into the abandonment, or bay-fill deposits beneath.
  
 
=== Locality 2, Greetland Quarry [SE 095 216] ===
 
=== Locality 2, Greetland Quarry [SE 095 216] ===
  
Access to the quarry is by the steps and footpath at the top of the road behind Coronation Street, which can be reached from Clayhouse Lane off the B6113 Ripponden Road. The quarry face provides a rare example of lateral accretion surfaces within the braided river sandbody of the Rough Rock, structures which are more typical of point bars in meandering rather than braided river systems. The 6.5&nbsp;m high quarry face exposes a series of 30&nbsp;m long lateral accretion surfaces dipping at <15°, but decreasing in dip and flattening to the west where they appear to be overlain and draped by cross-stratified sandstone deposited by currents flowing to the west. Lateral accretion units defined by these bounding surfaces contain mainly small-scale cross-stratification, trending southwards out of the quarry face at a high angle to the bounding surfaces. Water escape structures and undulatory laminations occur at the westernmost end of the outcrop, above a 2&nbsp;m thick cross-stratified unit. The sandstone is coarse to very coarse-grained but with no systematic variation in the grain size or scale of the sedimentary structures within individual lateral accretion units, a feature which is atypical of point bars.
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Access to the quarry is by the steps and footpath at the top of the road behind Coronation Street, which can be reached from Clayhouse Lane off the B6113 Ripponden Road. The quarry face provides a rare example of lateral accretion surfaces within the braided river sandbody of the Rough Rock, structures which are more typical of point bars in meandering rather than braided river systems. The 6.5 m high quarry face exposes a series of 30 m long lateral accretion surfaces dipping at <15°, but decreasing in dip and flattening to the west where they appear to be overlain and draped by cross-stratified sandstone deposited by currents flowing to the west. Lateral accretion units defined by these bounding surfaces contain mainly small-scale cross-stratification, trending southwards out of the quarry face at a high angle to the bounding surfaces. Water escape structures and undulatory laminations occur at the westernmost end of the outcrop, above a 2 m thick cross-stratified unit. The sandstone is coarse to very coarse-grained but with no systematic variation in the grain size or scale of the sedimentary structures within individual lateral accretion units, a feature which is atypical of point bars.
  
 
At the eastern end of the quarry face, the accretion surfaces steepen and are replaced by large-scale cross-stratification within a coarser-grained, more pebbly sandstone, possibly representing the nucleus around which the sandbody accumulated (Bristow, 1993), probably as a large medial bar within the Rough Rock braided distributary channel system.
 
At the eastern end of the quarry face, the accretion surfaces steepen and are replaced by large-scale cross-stratification within a coarser-grained, more pebbly sandstone, possibly representing the nucleus around which the sandbody accumulated (Bristow, 1993), probably as a large medial bar within the Rough Rock braided distributary channel system.
  
=== Locality 3, Elland Road Cutting [SE 103 215] ===
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=== Localiy 3, Elland Road Cutting [SE 103 215] ===
  
 
The road cutting lies on the A629 Elland bypass (Calderdale Way), some 4&nbsp;km south of Halifax town centre, and illustrates a fluvially dominated prograding delta system. Because of heavy traffic, and its location on a bend in the road, care must be taken when examining the outcrop. The safest, most convenient parking is on the extensive grass verge at the southern end of the cutting. The cutting varies in height from 15 to 30&nbsp;m and can be traced laterally for some 500&nbsp;m. The outcrop, which is orientated north-northeast–south-southwest, approximately parallel to the local and regional palaeoflow direction, consists of three well-defined channel sandbodies overlying finer-grained rippled sandstones and siltstones forming an overall coarsening-upward sequence ([[:File:YGS_YORKROCK_FIG_09_02.jpg|Figure 9.2]]b). The sandstones and siltstones are sharply overlain by medium-grained micaceous sandstones, internally structured by downcurrent-dipping bedding surfaces, defining downstream accreting beds, containing trough cross-stratification and occasional plane lamination. The sandstone and siltstone beds at the base of the outcrop were deposited in the distal part of a delta system with the overlying coarser-grained sands laid down in a more proximal (landward) mouth bar setting as the delta prograded basinwards.
 
The road cutting lies on the A629 Elland bypass (Calderdale Way), some 4&nbsp;km south of Halifax town centre, and illustrates a fluvially dominated prograding delta system. Because of heavy traffic, and its location on a bend in the road, care must be taken when examining the outcrop. The safest, most convenient parking is on the extensive grass verge at the southern end of the cutting. The cutting varies in height from 15 to 30&nbsp;m and can be traced laterally for some 500&nbsp;m. The outcrop, which is orientated north-northeast–south-southwest, approximately parallel to the local and regional palaeoflow direction, consists of three well-defined channel sandbodies overlying finer-grained rippled sandstones and siltstones forming an overall coarsening-upward sequence ([[:File:YGS_YORKROCK_FIG_09_02.jpg|Figure 9.2]]b). The sandstones and siltstones are sharply overlain by medium-grained micaceous sandstones, internally structured by downcurrent-dipping bedding surfaces, defining downstream accreting beds, containing trough cross-stratification and occasional plane lamination. The sandstone and siltstone beds at the base of the outcrop were deposited in the distal part of a delta system with the overlying coarser-grained sands laid down in a more proximal (landward) mouth bar setting as the delta prograded basinwards.

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