Editing Permian rocks of south-central Yorkshire - an excursion

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Fields immediately southeast of Locality 2 comprise a '''dip'''-slope, which is cut by a southwest–northeast fault that '''throws''' up Coal Measures to the southeast and brings in a second Permian escarpment at Bilham Sand Quarry (Locality 1).
 
Fields immediately southeast of Locality 2 comprise a '''dip'''-slope, which is cut by a southwest–northeast fault that '''throws''' up Coal Measures to the southeast and brings in a second Permian escarpment at Bilham Sand Quarry (Locality 1).
  
=== Locality 3 [SE 4808), Hooton Pagnell village (45 mins) ===
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=== Locality 3 [SE 4808), Hooton Pagnell village (45 mins) ===
  
 
There are several parking places, the largest just north of the church. '''No hammers please!''' This picturesque village, which has changed little for several centuries and featured in the Domesday Book, is built on solid rock in the scarp and crest of the Permian Escarpment. A leisurely stroll around the houses (but watch out for traffic in the narrow roads) reveals a host of small rock exposures, scarcely two the same, and close scrutiny of the locally-derived shelly building stone and stone gateposts is particularly rewarding.
 
There are several parking places, the largest just north of the church. '''No hammers please!''' This picturesque village, which has changed little for several centuries and featured in the Domesday Book, is built on solid rock in the scarp and crest of the Permian Escarpment. A leisurely stroll around the houses (but watch out for traffic in the narrow roads) reveals a host of small rock exposures, scarcely two the same, and close scrutiny of the locally-derived shelly building stone and stone gateposts is particularly rewarding.
  
The rocks exposed are about 7 m thick, the lowest lying an estimated 3–4 m above the unconformity. They comprise a highly varied complex of small patch reefs, some compound, and surrounding shelly oolite. The reefs are roughly oval in cross-section and up to perhaps 40 m across; they mainly comprise buff finely crystalline dolomite arranged in a disorderly pile of sack-like masses ('saccoliths') each typically 1–3 m across and 0.6 m thick and containing a sparse framework of the small twig-like '''bryozoan''' ''Acanthocladia ''(an attached filter-feeder). The reefs interfinger with, and sharply abut against, the oolite which is generally similar to that seen at Locality 2 but is less shelly and contains, additionally, laminae and lenses of very finely crystalline dolomite (formerly carbonate mud) that fills shallow channels and drapes low-amplitude current ripples.
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The rocks exposed are about 7 m thick, the lowest lying an estimated 3–4 m above the unconformity. They comprise a highly varied complex of small patch reefs, some compound, and surrounding shelly oolite. The reefs are roughly oval in cross-section and up to perhaps 40 m across; they mainly comprise buff finely crystalline dolomite arranged in a disorderly pile of sack-like masses ('saccoliths') each typically 1–3 m across and 0.6 m thick and containing a sparse framework of the small twig-like bryozoan ''Acanthocladia ''(an attached filter-feeder). The reefs interfinger with, and sharply abut against, the oolite which is generally similar to that seen at Locality 2 but is less shelly and contains, additionally, laminae and lenses of very finely crystalline dolomite (formerly carbonate mud) that fills shallow channels and drapes low-amplitude current ripples.
  
The most instructive building stones are in walls of buildings at the south end of the main street where a spectacular range of grains include '''algal'''-coated shell debris, algal'-coated fragments of local Permian oolite up to 50 mm across, and almost infinitely varied ooliths, '''pisoliths''' and compound grains.
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The most instructive building stones are in walls of buildings at the south end of the main street where a spectacular range of grains include algal-coated shell debris, algal-coated fragments of local Permian oolite up to 50 mm across, and almost infinitely varied ooliths, pisoliths and compound grains.
  
 
The exposures at Hooton Pagnell convey a vivid image of a shallow, white-floored tropical sea with scattered small sub-circular to elongate darker-coloured reefs rising less than a metre above the surrounding sea floor. These provided ecological niches for abundant small organisms that would not have survived in the current-swept exposed areas between and around the reefs.
 
The exposures at Hooton Pagnell convey a vivid image of a shallow, white-floored tropical sea with scattered small sub-circular to elongate darker-coloured reefs rising less than a metre above the surrounding sea floor. These provided ecological niches for abundant small organisms that would not have survived in the current-swept exposed areas between and around the reefs.
  
=== Locality 4 [SE 483 116], Field Lane Quarry S.S.S.I. South Elmsall (40 mins) ===
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=== Locality 4 [SE 483 116], Field Lane Quarry S.S.S.I. South Elmsall (40 mins) ===
  
Park at the roadside beside the quarry. '''No hammers please; hard hats recommended.''' This unique exposure of an almost complete cross-section of a patch-reef near the middle of the Wetherby Member of the Cadeby Formation is typical of reefs at this stratigraphical level and lies in bedded oolitic and pisolitic shelly dolomite. It comprises a core (C on [[:File:YGS_YORKROCK_FIG_14_02.jpg|Figure 14.2]]) of massive dolomite with a densely packed but poorly preserved framework of small twiggy bryozoans (as at Hooton Pagnell), overlain by a mantle of conspicuously domed '''stromatolites''' [S on [[:File:YGS_YORKROCK_FIG_14_02.jpg|Figure 14.2]]). The latter contain no shelly fossils but grade laterally into the surrounding bedded dolomite in which the remains of the bivalves ''Bakevellia, Liebea ''and ''Schizodus'' are locally abundant.
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Park at the roadside beside the quarry. '''No hammers please; hard hats recommended.''' This unique exposure of an almost complete cross-section of a patch-reef near the middle of the Wetherby Member of the Cadeby Formation is typical of reefs at this stratigraphical level and lies in bedded oolitic and pisolitic shelly dolomite. It comprises a core (C on [[:File:YGS_YORKROCK_FIG_14_02.jpg|Figure 14.2]]) of massive dolomite with a densely packed but poorly preserved framework of small twiggy bryozoans (as at Hooton Pagnell), overlain by a mantle of conspicuously domed stromatolites [S on [[:File:YGS_YORKROCK_FIG_14_02.jpg|Figure 14.2]]). The latter contain no shelly fossils but grade laterally into the surrounding bedded dolomite in which the remains of the bivalves ''Bakevellia, Liebea ''and ''Schizodus'' are locally abundant.
  
 
The rocks exposed at South Elmsall, like those at Hooton Pagnell, were probably all formed in clear sea water no more than a few metres deep; there is no evidence of subaerial exposure or erosion.
 
The rocks exposed at South Elmsall, like those at Hooton Pagnell, were probably all formed in clear sea water no more than a few metres deep; there is no evidence of subaerial exposure or erosion.
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A notice board gives additional information and interpretation.
 
A notice board gives additional information and interpretation.
  
=== Locality 5 [SE 487 177], Wentbridge road cutting and quarry (45 mins) ===
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=== Locality5 [SE 487 177], Wentbridge road cutting and quarry (45 mins) ===
  
Park at the roadside, preferably on the west side north of the bend. The cutting is on the old A1 where it cuts through the escarpment of the Cadeby Formation; the scarp face here is particularly impressive, especially when viewed from the south of the River Went valley. The quarry is cut into the scarp in woodland on the east side of the road and some 70–100 m southeast of the cutting. Both cutting and quarry are somewhat overgrown in high summer, but well repay a little clearance.
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Park at the roadside, preferably on the west side north of the bend. The cutting is on the old At where it cuts through the escarpment of the Cadeby Formation; the scarp face here is particularly impressive, especially when viewed from the south of the River Went valley. The quarry is cut into the scarp in woodland on the east side of the road and some 70–100 m southeast of the cutting. Both cutting and quarry are somewhat overgrown in high summer, but well repay a little clearance.
  
The cutting exposes about 10 m of regularly bedded, partly '''cross-bedded''' oolitic dolomite of the Wetherby Member lying '''disconformably''' on Ackworth Rock sandstone of the early Upper Coal Measures. Some of the lower beds of the oolite contain many bivalves, especially ''Bakevellia ''and ''Schizodus.''
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The cutting exposes about 10 m of regularly bedded, partly cross-bedded oolitic dolomite of the Wetherby Member lying disconformably on Ackworth Rock sandstone of the early Upper Coal Measures. Some of the lower beds of the oolite contain many bivalves, especially ''Bakevellia ''and ''Schizodus.''
  
The quarry exposes a typical bryozoan patch-reef lying in shelly oolitic dolomite as seen in the cutting. The reef is about 35 m across and 3 m thick and is formed of an untidy assemblage of sack-like masses, similar to those in the reefs at Locality 3; it abuts sharply against the surrounding oolites which contain very little reef-derived debris. A second, smaller, reef is also present and about 0.3 m of yellow-buff friable fine- to medium-grained sandstone beneath the oolite near the quarry entrance may be Basal Permian Sand.
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The quarry exposes a typical bryozoan patch-reef lying in shelly oolitic dolomite as seen in the cutting. The reef is about 35 m across and 3 m thick and is formed of an untidy assemblage of sack-like masses, similar to those in the reefs at Locality 3; it abuts sharply against the surrounding oolites which contain very little reef-derived debris. A second, smaller, reef is also present and about 0.3 m of yellow-buff friable fine- to medium-grained sandstone beneath the oolite near the quarry entrance may be Basal Permian Sand.
  
 
The carbonate rocks at this locality were formed soon after the Zechstein Sea was created, probably under shallow clear sea water of normal salinity and moderate energy. The great abundance of bivalve casts near the base of the section is typical of the area and no reefs were formed before this shelly unit. The shells probably afforded a firm sea floor for the attachment of the reef-building bryozoans.
 
The carbonate rocks at this locality were formed soon after the Zechstein Sea was created, probably under shallow clear sea water of normal salinity and moderate energy. The great abundance of bivalve casts near the base of the section is typical of the area and no reefs were formed before this shelly unit. The shells probably afforded a firm sea floor for the attachment of the reef-building bryozoans.
  
=== Locality 6 [SE 4713 2788], Fairburn village (20 mins)===
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=== Locality 6 [SE 4713 2788], Fairburn village ===
  
Visit the two exposures at the foot of the high wall on the northeast side of the road and about 60–90 m northwest of The Three Horse Shoes public house . There is parking almost opposite the exposure. '''No hammering please.'''
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Fairburn village, two exposures at the foot of the high wall on the northeast side of the road and about 60–go m northwest of The Three Horse Shoes public house (20 mins). There is parking almost opposite the exposure. '''No hammering please.'''
  
The Brotherton Formation (Cycle EZ3) is extremely uniform in this part of Yorkshire and where seen here is typical of much of the surrounding area except that it is dolomite. It comprises unevenly flaggy to thin-bedded finely crystalline buff dolomite with a variety of sedimentary structures (cross-lamination, ripples, cut and fill structures, etc.) that are suggestive of shallow-water accumulation. Some beds are graded, perhaps through being reworked during storms. Most beds are sparingly shelly but some are highly fossiliferous. Only two genera of bivalves — ''Liebea ''and ''Schizodus — ''are generally present, together with the 1 x 10 mm stick-like tubular remains of the supposed alga ''Calcinema. ''These remains, which occur locally in rock-forming proportions, commonly form aligned swarms on bedding planes. Salinity may have been slightly above normal and energy was generally low to moderate.
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The Brotherton Formation (Cycle EZ3) is extremely uniform in this part of Yorkshire and where seen here is typical of much of the surrounding area except that it is dolomite. It comprises unevenly flaggy to thin-bedded finely crystalline buff dolomite with a variety of sedimentary structures (cross-lamination, ripples, cut and fill structures, etc.) that are suggestive of shallow-water accumulation. Some beds are graded, perhaps through being reworked during storms. Most beds are sparingly shelly but some are highly fossiliferous. Only two genera of bivalves — ''Liebea ''and ''Schizodus — ''are generally present, together with the 1 x io mm stick-like tubular remains of the supposed alga ''Calcinema. ''These remains, which occur locally in rock-forming proportions, commonly form aligned swarms on bedding planes. Salinity may have been slightly above normal and energy was generally low to moderate.
  
 
Limestone of the upper part of the Brotherton Formation was formerly widely worked in and around Brotherton, Ferrybridge and Knottingley but although quarrying has now almost ceased, hundreds of local walls and buildings testify to the vast amount of rock extracted and provide readily accessible examples of most of the rock-types present. The effects of differential subsidence caused by Tertiary or later dissolution of evaporites in the underlying Edlington Formation is seen in most of the quarry faces around Brotherton in the form of gentle sags, folds and minor faults.
 
Limestone of the upper part of the Brotherton Formation was formerly widely worked in and around Brotherton, Ferrybridge and Knottingley but although quarrying has now almost ceased, hundreds of local walls and buildings testify to the vast amount of rock extracted and provide readily accessible examples of most of the rock-types present. The effects of differential subsidence caused by Tertiary or later dissolution of evaporites in the underlying Edlington Formation is seen in most of the quarry faces around Brotherton in the form of gentle sags, folds and minor faults.
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There are many quarry faces of limestone of the Brotherton Formation east of the A1. For those with time to spare, or those travelling southwards, excellent exposures are to be found at Brotherton [SE 481 267] and Knottingley [SE 498 239].
 
There are many quarry faces of limestone of the Brotherton Formation east of the A1. For those with time to spare, or those travelling southwards, excellent exposures are to be found at Brotherton [SE 481 267] and Knottingley [SE 498 239].
  
=== Locality 7 [SE 446 324], Micklefield Quarry S.S.S.I. (40 mins) ===
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=== Locality 7 [SE 446 324], Micklefield Quarry S.S.S.I. (40 mins) ===
  
 
Park in the quarry, behind the houses. '''No hammering please; hard hats recommended.''' An important section that exposes the Hampole Beds and adjoining parts of the Wetherby and Sprotbrough members of the Cadeby Formation (EZ1Ca) (see [[:File:YGS_YORKROCK_TAB_14_02.jpg|Table 14.2]]).
 
Park in the quarry, behind the houses. '''No hammering please; hard hats recommended.''' An important section that exposes the Hampole Beds and adjoining parts of the Wetherby and Sprotbrough members of the Cadeby Formation (EZ1Ca) (see [[:File:YGS_YORKROCK_TAB_14_02.jpg|Table 14.2]]).
  
The Hampole Beds record a phase when the sea level fell by a few metres and subsequently rapidly recovered. The sea level fall led to subaerial exposure and the cutting of the Hampole Discontinuity, an erosion surface that can be traced from Ripon to Nottingham, and the return of the sea caused the shoreline to retreat westwards. The area then became part of a north–south offshore belt of large white submarine sand waves composed of ooliths. The sediment below the sea floor at this time was able to support a variety of burrowing organisms but the current-swept sea floor itself was an inhospitable and dangerous place and few invertebrates survived to be preserved as fossils. The 'fenestral fabric' in the lower part of the Hampole Beds is thought to have been caused by the expansion of trapped methane bubbles given off by decaying organic (microbial) films ('algal mats') in the laminated intertidal sediment. The 0.8 m bed in which it is present is an excellent and readily recognizable building stone and features in most of the stone-built houses and walls in New Micklefield.
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The Hampole Beds record a phase when the sea level fell by a few metres and subsequently rapidly recovered. The sea level fall led to subaerial exposure and the cutting of the Hampole Discontinuity, an erosion surface that can be traced from Ripon to Nottingham, and the return of the sea caused the shoreline to retreat westwards. The area then became part of a north–south offshore belt of large white submarine sand waves composed of ooliths. The sediment below the sea floor at this time was able to support a variety of burrowing organisms but the current-swept sea floor itself was an inhospitable and dangerous place and few invertebrates survived to be preserved as fossils. The 'fenestral fabric' in the lower part of the Hampole Beds is thought to have been caused by the expansion of trapped methane bubbles given off by decaying organic (microbial) films ('algal mats') in the laminated intertidal sediment. The 0.8 m bed in which it is present is an excellent and readily recognizable building stone and features in most of the stone-built houses and walls in New Micklefield.
  
 
A notice board gives additional information and interpretation.
 
A notice board gives additional information and interpretation.

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