Editing Magnesian Limestone between South Shields and Seaham - an excursion

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Park at the northwest end of Marsden Lea car park [NZ 397 651] then take the steps to the beach, turning right at the bottom and walk southeast (no farther than the tall narrow stack). The cliffs here are formed mainly of 16–20 m of cream and buff fine-grained dolostone of the Concretionary Limestone Formation. Concentrate for the first 135 m on the general appearance of the rock face from a distance, for this is one of the best places in Britain for seeing the effects of foundering caused by the dissolution of underlying '''evaporites'''. All the strata have foundered by about the same amount (?60–100 m) but some parts have been let down gently and without much dislocation whereas others have had a more complex history of subsidence and are intensely fractured (''''breccia'''-gashes'). After the first 135 m inspect the rock in detail. As at Locality 2, it comprises a mixture of finely laminated and unlaminated rock, here mainly fine-grained buff dolostone but also includes unlaminated '''oolite'''; some of the unlaminated beds, including the oolite, contain moulds of ''Liebea, Permophorus ''and ''Schizodus, ''many are graded and some have tight folds and shear-planes caused by downslope slumping and sliding. The inferred depositional environment is as for Locality 2.
 
Park at the northwest end of Marsden Lea car park [NZ 397 651] then take the steps to the beach, turning right at the bottom and walk southeast (no farther than the tall narrow stack). The cliffs here are formed mainly of 16–20 m of cream and buff fine-grained dolostone of the Concretionary Limestone Formation. Concentrate for the first 135 m on the general appearance of the rock face from a distance, for this is one of the best places in Britain for seeing the effects of foundering caused by the dissolution of underlying '''evaporites'''. All the strata have foundered by about the same amount (?60–100 m) but some parts have been let down gently and without much dislocation whereas others have had a more complex history of subsidence and are intensely fractured (''''breccia'''-gashes'). After the first 135 m inspect the rock in detail. As at Locality 2, it comprises a mixture of finely laminated and unlaminated rock, here mainly fine-grained buff dolostone but also includes unlaminated '''oolite'''; some of the unlaminated beds, including the oolite, contain moulds of ''Liebea, Permophorus ''and ''Schizodus, ''many are graded and some have tight folds and shear-planes caused by downslope slumping and sliding. The inferred depositional environment is as for Locality 2.
  
=== Locality 4 [NZ 407 596], Roker promenade, Sunderland (40 mins) ===
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=== Locality 4 [NZ 407 596], Roker promenade, Sunderland (40 mins) ===
  
Park in any of several east–west residential roads off the coast road and (from NZ 4068 5961) proceed down the steps to the beach, noting the large blocks of Concretionary Limestone beside the steps, probably from Fulwell quarries 2 km to the west. Turn right at the bottom, to inspect the c.8 m cliff of Roker Dolomite dolostone. This is unevenly bedded and '''dips''' gently southwards; it is cream and buff, mainly finely oolitic, soft and porous, and most of the '''ooliths''' have hollow centres. Tabular '''cross-lamination''' is present and thin beds of mud- or silt-grade dolostone drape broad low-amplitude ripples. Several disturbed beds up to 0.6 m thick, probably debris-flows, lie on scoured surfaces. Moulds of ''Liebea ''and ''Schizodus ''occur in some beds. These rocks were probably formed high on the basin-margin slope, in well-oxygenated water of moderate energy.
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Park in any of several east–west residential roads off the coast road and (from NZ 40685961) proceed down the steps to the beach, noting the large blocks of Concretionary Limestone beside the steps, probably from Fulwell quarries 2 km to the west. Turn right at the bottom, to inspect the c.8 m cliff of Roker Dolomite dolostone. This is unevenly bedded and '''dips''' gently southwards; it is cream and buff, mainly finely oolitic, soft and porous, and most of the '''ooliths''' have hollow centres. Tabular '''cross-lamination''' is present and thin beds of mud- or silt-grade dolostone drape broad low-amplitude ripples. Several disturbed beds up to 0.6 m thick, probably debris-flows, lie on scoured surfaces. Moulds of ''Liebea ''and ''Schizodus ''occur in some beds. These rocks were probably formed high on the basin-margin slope, in well-oxygenated water of moderate energy.
  
The famous 'Cannon-Ball Rocks' are the second main feature of interest at Roker. They form a rounded mass against the promenade just north of the steps and comprise a tightly-packed assemblage of subspherical calcite concretions with patches of inter-concretion fine-grained buff dolomite. The concretions are up to 0.25 m in diameter and most are concentrically laminated and partly coarsely radially crystalline.
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The famous 'Cannon-Ball Rocks' are the second main feature of interest at Roker. They form a rounded mass against the promenade just north of the steps and comprise a tightly-packed assemblage of subspherical calcite concretions with patches of inter-concretion fine-grained buff dolomite. The concretions are up to 0.25 m in diameter and most are concentrically laminated and partly coarsely radially crystalline.
  
=== Locality 5 [NZ 357 576], Castletown river cliff (except at high tide); (40 mins) ===
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=== Locality 5 [NZ 357 576], Castletown river cliff (except at high tide); (40 mins) ===
  
Wellingtons can be an advantage in approaching this exposure. Park in Sunderland Enterprise Park [NZ 3578 5672] and take the footpath signposted 'Hylton Riverside' to the south-southeast through a narrow wooded valley to the riverside. Here the exposure on your left comprises Yellow Sands (6 m+) resting unconformably on Upper Coal Measures sandstone (2 m+). This is the only good exposure of the unconformity in the Sunderland area; it is an almost plane erosion surface and represents a time gap of at least 40 Ma. The underlying sandstone, except for the uppermost 0.3 m, has been reddened by desert weathering and is the youngest permanently exposed Carboniferous stratum in northeast England. The Yellow Sands is a typical desert dune formation; it is weakly cemented (but with patchy well-cemented nodules) in a parallel-laminated coarse-grained basal unit (c.1 m thick) and strongly trough cross-bedded in the remainder where it is medium- to coarse-grained and almost incohesive. The sand is cut by several minor faults and fissures, some of which harbour downward-tapering brown clay probably squeezed down from the Marl Slate when the faults and fissures were created.
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Wellingtons can be an advantage in approaching this exposure. Park in Sunderland Enterprise Park [NZ 35785 672] and take the footpath signposted 'Hylton Riverside' to the south-southeast through a narrow wooded valley to the riverside. Here the exposure on your left comprises Yellow Sands (6 m+) resting unconformably on Upper Coal Measures sandstone (2 m+). This is the only good exposure of the unconformity in the Sunderland area; it is an almost plane erosion surface and represents a time gap of at least 40 Ma. The underlying sandstone, except for the uppermost 0.3 m, has been reddened by desert weathering and is the youngest permanently exposed Carboniferous stratum in northeast England. The Yellow Sands is a typical desert dune formation; it is weakly cemented (but with patchy well-cemented nodules) in a parallel-laminated coarse-grained basal unit (c.1 m thick) and strongly trough cross-bedded in the remainder where it is medium- to coarse-grained and almost incohesive. The sand is cut by several minor faults and fissures, some of which harbour downward-tapering brown clay probably squeezed down from the Marl Slate when the faults and fissures were created.
  
 
=== Locality 6 [NZ 391 545] Tunstall Hills S.S.S.I. (40 mins) ===
 
=== Locality 6 [NZ 391 545] Tunstall Hills S.S.S.I. (40 mins) ===

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