Editing Geological history of Yorkshire

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== Carboniferous ==
 
== Carboniferous ==
  
Carboniferous sedimentation was dominated by cycles of transgression and '''regression''' on several scales. The six stages of the Dinantian (early Mississippian) are based on '''mesothem''' cycles with calcareous shales and richly fossiliferous, sometimes bituminous limestones characteristic of the transgressive phase, and '''oolitic''' limestones, '''algal''' limestones, '''dolomites''' and in places sandstones, pebble beds and '''disconformities''' marking the regressive phase in shallow waters. In the Craven Basin, where the Dinanthian sequence is some 3 km thick, early sediments are bioclastic limestones and calcareous shales but, episodic earth movements from mid-Dinantian into Namurian times resulted in northeast–southwest folding and increased subsidence in which '''goniatite'''-bearing, deep-water shales predominated. In the transition zone between the Craven Basin and the Askrigg Block, and around Clitheroe, marginal reef limestones were developed between basin and block in mid and late Dinantian times ([[Craven Fault Zone — Malham to Settle - an excursion|Excursion 2]]). In the Stainmore Trough, subsidence and sedimentation more nearly kept pace and neither significant deep water '''facies''', nor reef facies, were developed. The Askrigg Block, on which the Dinantian is less than 500 m thick, was not completely inundated by the sea until late Dinantian times ([[Craven Fault Zone — Malham to Settle - an excursion|Excursion 2]], [[Carboniferous rocks of upper Nidderdale - an excursion|Excursion 5]], [[Dinantian and Namurian rocks of Bolton Abbey and Trollers Gill - an excursion|Excursion 6]]). Minor sedimentary cycles become increasingly apparent within the topmost mesothem, with many repetitions of marine limestone succeeded by shale, sandstone and in places '''seatearth''' and coal. These are '''Yoredale''' cycles, a term derived from the old name for Wensleydale, where they are classically developed. The limestone component dominates at lower levels and towards the southern part of the Askrigg Block where open marine conditions prevailed. The elastic sediments increased in proportion in younger cycles and to the north, reflecting the increasing influence of southward '''prograding''' deltas. The Dinantian limestones are commonly rich in '''corals, brachiopods''' and '''foraminifera''', all of which help to date and correlate the sequences.
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Carboniferous sedimentation was dominated by cycles of transgression and regression on several scales. The six stages of the Dinantian (early Mississippian) are based on mesothem cycles with calcareous shales and richly fossiliferous, sometimes bituminous limestones characteristic of the transgressive phase, and oolitic limestones, algal limestones. dolomites and in places sandstones, pebble beds and disconformities marking the regressive phase in shallow waters. In the Craven Basin, where the Dinanthian sequence is some 3 km thick, early sediments are bioclastic limestones and calcareous shales but, episodic earth movements from mid-Dinantian into Namurian times resulted in northeast–southwest folding and increased subsidence in which goniatite-bearing, deep-water shales predominated. In the transition zone between the Craven Basin and the Askrigg Block, and around Clitheroe, marginal reef limestones were developed between basin and block in mid and late Dinantian times ([[Craven Fault Zone — Malham to Settle - an excursion|Excursion 2]]). In the Stainmore Trough, subsidence and sedimentation more nearly kept pace and neither significant deep water fades, nor reef facies, were developed. The Askrigg Block, on which the Dinantian is less than 500 m thick, was not completely inundated by the sea until late Dinantian times ([[Craven Fault Zone — Malham to Settle - an excursion|Excursion 2]], [[Carboniferous rocks of upper Nidderdale - an excursion|Excursion 5]], [[Dinantian and Namurian rocks of Bolton Abbey and Trollers Gill - an excursion|Excursion 6]]). Minor sedimentary cycles become increasingly apparent within the topmost mesothem, with many repetitions of marine limestone succeeded by shale, sandstone and in places seatearth and coal. These are Yoredale cycles, a term derived from the old name for Wensleydale, where they are classically developed. The limestone component dominates at lower levels and towards the southern part of the Askrigg Block where open marine conditions prevailed. The elastic sediments increased in proportion in younger cycles and to the north, reflecting the increasing influence of southward prograding deltas. The Dinantian limestones are commonly rich in corals, brachiopods and foraminifera, all of which help to date and correlate the sequences.
  
 
The Yoredale facies extends up into the Namurian, but from south to north across the county is replaced at progressively younger horizons by the thick and often coarse-grained fluviatile and deltaic sandstones of the Millstone Grit ([[Carboniferous rocks of upper Nidderdale - an excursion|Excursion 5]], [[Dinantian and Namurian rocks of Bolton Abbey and Trollers Gill - an excursion|Excursion 6]], [[Millstone Grit of Almscliff Crag and Harlow Car, near Harrogate - an excursion|Excursion 7]], [[Carboniferous (Namurian and Westphalian) of the Cliviger Valley, Todmorden - an excursion|Excursion 8]], [[Upper Carboniferous of the Halifax area - an excursion|Excursion 9]], [[Middle and Upper Carboniferous rocks (Millstone Grit and Coal Measures) of the Sheffield region - an excursion|Excursion 10]]). By early Namurian times, the clearly defined basin and block topography had largely disappeared, although subsidence rates remained highest, and sedimentary sequences therefore thickest, in the basinal areas. In the Craven Basin, the succession reaches 2.5 km in thickness, in contrast to a mere 370 m on the Askrigg Block and 500 m at Stainmore. These sediments were deposited from river systems flowing predominantly southwestwards into the area. As the deltas advanced, turbidites locally formed on basinal slopes in front of them, over which the deltaic and fluviatile sediments prograded, often building up to sea level to form forested flood plains and swamps. Episodic transgressions of the sea across the delta top resulted in the deposition of thin marine bands with goniatites, vital for dating and correlation.
 
The Yoredale facies extends up into the Namurian, but from south to north across the county is replaced at progressively younger horizons by the thick and often coarse-grained fluviatile and deltaic sandstones of the Millstone Grit ([[Carboniferous rocks of upper Nidderdale - an excursion|Excursion 5]], [[Dinantian and Namurian rocks of Bolton Abbey and Trollers Gill - an excursion|Excursion 6]], [[Millstone Grit of Almscliff Crag and Harlow Car, near Harrogate - an excursion|Excursion 7]], [[Carboniferous (Namurian and Westphalian) of the Cliviger Valley, Todmorden - an excursion|Excursion 8]], [[Upper Carboniferous of the Halifax area - an excursion|Excursion 9]], [[Middle and Upper Carboniferous rocks (Millstone Grit and Coal Measures) of the Sheffield region - an excursion|Excursion 10]]). By early Namurian times, the clearly defined basin and block topography had largely disappeared, although subsidence rates remained highest, and sedimentary sequences therefore thickest, in the basinal areas. In the Craven Basin, the succession reaches 2.5 km in thickness, in contrast to a mere 370 m on the Askrigg Block and 500 m at Stainmore. These sediments were deposited from river systems flowing predominantly southwestwards into the area. As the deltas advanced, turbidites locally formed on basinal slopes in front of them, over which the deltaic and fluviatile sediments prograded, often building up to sea level to form forested flood plains and swamps. Episodic transgressions of the sea across the delta top resulted in the deposition of thin marine bands with goniatites, vital for dating and correlation.

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