Editing Dinantian and Namurian depositional systems in the southern North Sea

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At outcrop, the base of this unit is drawn at the base of the Great Limestone, which roughly coincides with the ''Cravenoceras leion ''Marine Band of the basinal succession. Its age in the northern Pennines and Northumberland is Pendleian to early Kinderscoutian. Strata of Chokierian–Alportian age are not certainly present, suggesting a hiatus in the succession, although no mappable unconformity has yet been detected. The Upper Limestone Group includes some thick multi-storey channel sandbodies, which are most likely incised palaeovalleys (e.g. Elliott 1976, Hodge & Dunham 1991).
 
At outcrop, the base of this unit is drawn at the base of the Great Limestone, which roughly coincides with the ''Cravenoceras leion ''Marine Band of the basinal succession. Its age in the northern Pennines and Northumberland is Pendleian to early Kinderscoutian. Strata of Chokierian–Alportian age are not certainly present, suggesting a hiatus in the succession, although no mappable unconformity has yet been detected. The Upper Limestone Group includes some thick multi-storey channel sandbodies, which are most likely incised palaeovalleys (e.g. Elliott 1976, Hodge & Dunham 1991).
  
Offshore, the base of the Upper Limestone Group is drawn at a thick limestone that coincides broadly with an upward change to a more sandstone-rich succession. In most wells in the north, the limestone is sufficiently prominent for the boundary to be quite confidently identified. Farther south, the boundary changes character, along with the overall sedimentology, to a more basinal aspect. At well 41/24a-2, a condensed mudstone interval with prominent inferred marine bands is thought to equate with the boundary, whereas in intermediate wells (41/14-1, 41/15-1) inferred marine-band mudstones and thin limestones seem to coincide broadly. The base-Permian erosion truncates the Upper Limestone Group and makes for rather patchy preservation. Most recorded thicknesses are minimum values. These range up to just over 300 m on the Mid North Sea High. Farther south in the Cleveland Basin onshore, thicknesses exceed 500 m in the Cloughton-1 and Kirby Misperton-1 wells, and just offshore at well 41/24a-2. The lesser thickness of 415 m at 41/20-1 suggests that original depositional thicknesses probably decreased to the north. Farther north onshore, a reduced thickness (268 m) at Harton-1 was attributed by Ridd et al. (1970) to the early incoming of Millstone Grit facies. However, the recognition of Millstone Grit facies is considered somewhat insecure (Holliday, personal communication 2003) and the thickness could therefore be greater. At Seal Sands-1, base-Permian erosion prevents meaningful comparison of thicknesses, and it is not easy to judge how far into the Namurian the highly differential subsidence seen in the Dinantian persisted. By analogy (e.g. with the Craven Basin), it is likely that differential movements were much reduced.
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Offshore, the base of the Upper Limestone Group is drawn at a thick limestone that coincides broadly with an upward change to a more sandstone-rich succession. In most wells in the north, the limestone is sufficiently prominent for the boundary to be quite confidently identified. Farther south, the boundary changes character, along with the overall sedimentology, to a more basinal aspect. At well 41/24a-2, a condensed mudstone interval with prominent inferred marine bands is thought to equate with the boundary, whereas in intermediate wells (41/14-1, 41/15-1) inferred marine-band mudstones and thin limestones seem to coincide broadly. The base-Permian erosion truncates the Upper Limestone Group and makes for rather patchy preservation. Most recorded thicknesses are minimum values. These range up to just over 300m on the Mid North Sea High. Farther south in the Cleveland Basin onshore, thicknesses exceed 500m in the Cloughton-1 and Kirby Misperton-1 wells, and just offshore at well 41/24a-2. The lesser thickness of 415m at 41/20-1 suggests that original depositional thicknesses probably decreased to the north. Farther north onshore, a reduced thickness (268m) at Harton-1 was attributed by Ridd et al. (1970) to the early incoming of Millstone Grit facies. However, the recognition of Millstone Grit facies is considered somewhat insecure (Holliday, personal communication 2003) and the thickness could therefore be greater. At Seal Sands-1, base-Permian erosion prevents meaningful comparison of thicknesses, and it is not easy to judge how far into the Namurian the highly differential subsidence seen in the Dinantian persisted. By analogy (e.g. with the Craven Basin), it is likely that differential movements were much reduced.
  
 
In the north (e.g. 41/10-1 and in Northumberland), the Upper Limestone Group shows a broadly Yoredale character, with limestones present at the bases of many cyclothems. Farther south, towards the Cleveland Basin (e.g. wells 42/24a-2, 41/14-1, 41/15-1), thicker and apparently rather silty upwards-coarsening units are prominent, and limestones are scarce or absent. This suggests a transition southwards into deeper water, where marine bands replace limestones as records of highstands, and where progradations of fine-grained slopes were more important.
 
In the north (e.g. 41/10-1 and in Northumberland), the Upper Limestone Group shows a broadly Yoredale character, with limestones present at the bases of many cyclothems. Farther south, towards the Cleveland Basin (e.g. wells 42/24a-2, 41/14-1, 41/15-1), thicker and apparently rather silty upwards-coarsening units are prominent, and limestones are scarce or absent. This suggests a transition southwards into deeper water, where marine bands replace limestones as records of highstands, and where progradations of fine-grained slopes were more important.

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