Editing Upper Carboniferous of the Halifax area - an excursion

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=== Locality 3, Elland Road Cutting [SE 103 215] ===
 
=== Locality 3, Elland Road Cutting [SE 103 215] ===
  
The road cutting lies on the A629 Elland bypass (Calderdale Way), some 4 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 m and can be traced laterally for some 500 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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The road cutting lies on the A629 Elland bypass (Calderdale Way), some 4 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 m and can be traced laterally for some 500 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 mouth bar sands are overlain by two coarse to very coarse, mainly trough cross-stratified, erosive, channel sandbodies forming concave lenses up to 7 m thick and 300 m wide, interpreted as delta distributary channel sandbodies deposited by palaeocurrents flowing to the southeast. The top of these amalgamated sandbodies is truncated by the sediments above, or conformably overlain by a locally developed thin lens of fine sandstone and siltstone indicative of channel shifting and abandonment. The upper channel sandbody differs from those below in its multistorey sheet-like geometry and internal scour surfaces, commonly strewn with wood fragments. It is an erosively based, coarse to very coarse, granular, '''feldspathic''' sandstone, internally dominated by trough and solitary planar cross-stratification, deposited by palaeocurrents flowing south. Deformed foresets occur near the top of the outcrop.
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The mouth bar sands are overlain by two coarse to very coarse, mainly trough cross-stratified, erosive, channel sandbodies forming concave lenses up to 7 m thick and 300 m wide, interpreted as delta distributary channel sandbodies deposited by palaeocurrents flowing to the southeast. The top of these amalgamated sandbodies is truncated by the sediments above, or conformably overlain by a locally developed thin lens of fine sandstone and siltstone indicative of channel shifting and abandonment. The upper channel sandbody differs from those below in its multistorey sheet-like geometry and internal scour surfaces, commonly strewn with wood fragments. It is an erosively based, coarse to very coarse, granular, feldspathic sandstone, internally dominated by trough and solitary planar cross-stratification, deposited by palaeocurrents flowing south. Deformed foresets occur near the top of the outcrop.
  
 
The sandstone is correlated with the Rough Rock, and is thought to have been deposited in a braided river channel characterized by low to moderate discharge fluctuations. The thickness and lateral continuity of the sediments at this locality indicate that the delta supplied by this river system was probably of the shallow water, lobate type.
 
The sandstone is correlated with the Rough Rock, and is thought to have been deposited in a braided river channel characterized by low to moderate discharge fluctuations. The thickness and lateral continuity of the sediments at this locality indicate that the delta supplied by this river system was probably of the shallow water, lobate type.

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