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Volume 30: British Lower Jurassic Stratigraphy — Chapter 03
 

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Chap 01
19 figures
2 tables
Chap 02
32 figures
1 table
Chap 03
23 figures
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Chap 04
22 figures
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Chap 05
16 figures
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Chap 06
25 figures
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Chap 07
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Chap 08
21 figures
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Figure 3.1
Geological sketch map of the Lavernock to St Mary’s Well Bay area. After Trueman (1920).

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Figure 3.2
Mudstones and limestones of the St Mary’s Well Bay Member overlain by the mudstone-dominated Lavernock Shale Member, as viewed from the west side of Lavernock Bay. The conspicuous limestone beds in the foreground lie immediately below the Planorbis Mudstones. (Photo: M.J. Simms.)

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Figure 3.3
Section through the Blue Lias Formation in Lavernock Bay, based on Waters and Lawrence (1987) and Trueman (1920). The sequence through the Lavernock Shale and Porthkerry members has been compiled from Trueman’s (1920) description and should be considered only provisional (see comments in main text). Bed numbers are those of Waters and Lawrence (1987), and Trueman (1920) in brackets.

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Figure 3.4
The section at St Mary’s Well Bay, showing the conspicuous tabular limestones of the Bull Cliff Member in the upper part of the cliff overlying the silty mudstones of the Langport Member of the Penarth Group, with prominent sandstones in the Cotham Member visible near the base of the cliff. (Photo: M.J. Simms.)

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Figure 3.6
Coastal section from Pant y Slade to Witches Point, showing lateral facies changes in the Lias Group. After Trueman (1922b).

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Figure 3.7
Coarsely bedded marginal facies of the Lias Group resting unconformably on Carboniferous Limestone at the western edge of the Slade Trough. The paler bed immediately above the unconformity, and wedging-out rapidly westwards, is the heavily mineralized boulder bed unique to the Slade Trough. The person, for scale, is standing on the unconformity surface immediately west of the boulder bed (Photo: M.J. Simms.)

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Figure 3.8
Lithological log of the lower part of the marginal facies of the Lias Group within and adjacent to the Slade Trough. After Fletcher (1988).

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Figure 3.9
Sketch map of the geology in the area around Viaduct Quarry and Hobbs Quarry.

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Figure 3.10
Marginal facies of the Hettangian and lowermost Sinemurian stages exposed in the main face of Viaduct Quarry, Shepton Mallet. (Photo: M.J. Simms.)

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Figure 3.11
Sketch section through the marginal facies of the Lias Group at Viaduct Quarry. Bed thicknesses in the upper part of the quarry face are only approximate.

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Figure 3.12
Near-horizontal marginal facies of the Lias Group resting unconformably on Carboniferous Limestone dipping steeply southwards (towards the camera) at Hobbs Quarry, Shepton Mallet. The hammer, for scale, is in the lower left of the picture. (Photo: M.J. Simms.)

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Figure 3.13
Sketch map showing the southern limits of the Planorbis to Bucklandi zones in the Radstock district and the distribution of the Armatum Bed, Jamesoni Limestone and Valdani Limestone. The letters B, K and H correspond to the approximate locations of the three GCR sites of Bowldish Quarry, Kilmersdon Road Quarry and Huish Colliery Quarry. After Donovan and Kellaway (1984).

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Figure 3.14
Lithostratigraphy and correlation of the Radstock GCR sites After Donovan and Kellaway (1984).

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Figure 3.15
The section at Bowldish Quarry, Radstock. The thick limestone towards the top is the Bucklandi Bed, overlain by the Spiriferina Bed and Turneri Clay. The lower part of the face is of more thinly bedded limestones and mudstones of the Planorbis Zone. (Photo: M.J. Simms.)

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Figure 3.16
The brachiopod Spiriferina walcotti, from the Spiriferina Bed at Bowldish Quarry, Radstock. The largest specimen is 43 mm across. Specimens from the T.R. Fry Collection, Bristol City Museum. (Photo: M.J. Simms.)

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Figure 3.17
The recently cleared face of Kilmersdon Road Quarry. The main face is in thinly bedded limestones and mudstone of the Planorbis and Liasicus zones, capped by the planed-off surface of the Bucklandi Bed. The thin Sinemurian succession and the thicker bioclastic limestones of the Armatum Bed and Jamesoni Limestone are exposed in the low face above the conspicuous ledge. (Photo: M.J. Simms.)

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Figure 3.18
Phosphatized specimens of Paltechioceras aureolum (left) and Echioceras raricostatum (right) from the Armatum Bed of Kilmersdon Road Quarry. Paltechioceras is 65 mm across. From the T.R. Fry Collection in Bristol City Museum. (Photo: M.J. Simms.)

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Figure 3.19
The limestone-dominated succession at Huish Colliery Quarry. The lower part of the face exposes limestones and thin mudstones of the Planorbis Zone, overlain by more massive bioclastic limestones of the Armatum Bed and Jamesoni Limestone in the upper part of the picture. (Photo: M.J. Simms.)

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Figure 3.20
Sketch map of the geology in the Cloford and Holwell area of the eastern Mendip Hills.

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Figure 3.21
Pull-apart, sediment-filled fissure (Fissure 24 of Figure 3.22) at Cloford Quarry. At least three distinct events are discernable in this example; (1) extension to form a 0.5 m-wide joint-guided pull-apart fissure subsequently filled with pale fine-grained sediment; (2) lateral offset of parts of this fissure by movement on a bedding plane (on which the hammer rests); (3) further extension to form a 0.1 m-wide fissure whose sediment fill (slightly darker and coarser than the earlier fill) is continuous across the bedding plane on which the earlier offset occurred. The bedding plane offset and opening of the second fissure probably represent different phases of the same extensional event. (Photo: M.J. Simms.)

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Figure 3.22
Sketch map of the distribution of Mesozoic fissures identified in Cloford Quarry in May 2000 (widths of fissures not to scale).

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Figure 3.23
Hildoceras (left) and Nodicoeloceras (right) from Fissure CXX at Cloford Quarry, indicating a Lower Toarcian Bifrons Zone age for the infill. Specimens from the Charles Copp Collection at Bristol City Museum. Nodicoeloceras is 50 mm across. (Photo: M.J. Simms.)

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Figure 3.24
Sketch of exposure at Leighton Road Cutting, as seen in 1977, and detail of succession. After Jenkyns and Senior (1991).

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