Editing Dinantian and Namurian depositional systems in the southern North Sea

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At Cloughton-1, by comparison, the high-gamma mudstones at base Namurian are clearly present, although somewhat thicker. The rest of the Pendleian comprises an upwards-coarsening unit but possible turbidite sandstones within it appear more thinly bedded. Immediately below the high-gamma mudstones are thick sandstones and inferred coal seams suggestive of a delta top setting and again indicating a significant deepening event around the Dinantian/Namurian boundary. The Cloughton-1 well terminated a short distance into the Dinantian so that the earlier history cannot be deduced.
 
At Cloughton-1, by comparison, the high-gamma mudstones at base Namurian are clearly present, although somewhat thicker. The rest of the Pendleian comprises an upwards-coarsening unit but possible turbidite sandstones within it appear more thinly bedded. Immediately below the high-gamma mudstones are thick sandstones and inferred coal seams suggestive of a delta top setting and again indicating a significant deepening event around the Dinantian/Namurian boundary. The Cloughton-1 well terminated a short distance into the Dinantian so that the earlier history cannot be deduced.
  
At Kirby Misperton-1, the Namurian section compares quite closely with that at Cloughton-1 and 41/24-1. The gamma peaks in the basal mudstone are less conspicuous and the large-scale upwards-coarsening succession of the Pendleian is thicker and has thicker channel sandbodies in its upper part. In contrast, inferred turbidite sandstones in the lower part of the pro-gradation are thin in comparison. The Dinantian strata just below the inferred Dinantian/Namurian boundary are similar to those in the other wells with channel sandstones but no obvious coals. This again suggests a significant deepening event at the Dinantian/Namurian boundary. However, the Dinantian penetration extends for some 1150 m and this provides a unique view of the earlier history of the Cleveland Basin. The latest Dinantian channel sandstones themselves occur at the top of a major fine-grained upwards-coarsening succession, some 300 m thick. Beneath that are some 300 m of thinly interbedded sandstones and finer grained rocks, which in turn overlie a sandy succession within which there are small-scale upwards-coarsening units that probably record minor deltaic progradations. The occurrence of a thick fine-grained upwards-coarsening unit above older deltaics suggests a phase of deepening. There is no control on the age of these deepest Dinantian sediments, but on thickness grounds they are likely to extend back at least well into the Asbian. The earlier phase of deepening could therefore be of Asbian age, but without tighter control on the age of the section in the deeper parts of the well, it is not possible to be more precise.
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At Kirby Misperton-1, the Namurian section compares quite closely with that at Cloughton-1 and 41/24-1. The gamma peaks in the basal mudstone are less conspicuous and the large-scale upwards-coarsening succession of the Pendleian is thicker and has thicker channel sandbodies in its upper part. In contrast, inferred turbidite sandstones in the lower part of the pro-gradation are thin in comparison. The Dinantian strata just below the inferred Dinantian/Namurian boundary are similar to those in the other wells with channel sandstones but no obvious coals. This again suggests a significant deepening event at the Dinantian/Namurian boundary. However, the Dinantian penetration extends for some 1150m and this provides a unique view of the earlier history of the Cleveland Basin. The latest Dinantian channel sandstones themselves occur at the top of a major fine-grained upwards-coarsening succession, some 300m thick. Beneath that are some 300m of thinly interbedded sandstones and finer grained rocks, which in turn overlie a sandy succession within which there are small-scale upwards-coarsening units that probably record minor deltaic progradations. The occurrence of a thick fine-grained upwards-coarsening unit above older deltaics suggests a phase of deepening. There is no control on the age of these deepest Dinantian sediments, but on thickness grounds they are likely to extend back at least well into the Asbian. The earlier phase of deepening could therefore be of Asbian age, but without tighter control on the age of the section in the deeper parts of the well, it is not possible to be more precise.
  
 
It is clear from well 43/17-2 [[:File:YGS_CHR_04_DINA_FIG_10.jpg|(Figure 10)]] that major deepening had occurred offshore prior to the Brigantian and, therefore, it might be reasonable to speculate that such movements were associated with those that caused the Dinantian deepening in the Cleveland Basin, which are tentatively inferred to be Asbian in age. A phase of well constrained Asbian extension is also recognized in the Craven Basin, although deepening of the sea began earlier here (Kirby et al. 2000). If this age were correct, the deepening in the southern North Sea would be broadly contemporaneous with the deposition of the Scremerston Formation. A consequence of the deeping is that the shallow-water strata of the Scremerston and Lower and Middle Limestone formations of the Mid North Sea High passed into deeper-water facies to the south, possibly with bypassing of sand to contemporaneous turbidite settings. This would compare with the spilling of sand across the Craven faults in the Brigantian to give turbidite units such as the Pendleside Sandstone in the Craven Basin as equivalents of Yoredale deltaic strata on the Askrigg Block. Another consequence is that the pre-deepening Cementstones, Fell Sandstone and the earlier parts of the Scremerston Formation may extend as fluvial and deltaic facies beneath the Southern North Sea Basin. This contrasts with what is seen onshore, where these units are mainly restricted to the Northumberland and Stainmore troughs.
 
It is clear from well 43/17-2 [[:File:YGS_CHR_04_DINA_FIG_10.jpg|(Figure 10)]] that major deepening had occurred offshore prior to the Brigantian and, therefore, it might be reasonable to speculate that such movements were associated with those that caused the Dinantian deepening in the Cleveland Basin, which are tentatively inferred to be Asbian in age. A phase of well constrained Asbian extension is also recognized in the Craven Basin, although deepening of the sea began earlier here (Kirby et al. 2000). If this age were correct, the deepening in the southern North Sea would be broadly contemporaneous with the deposition of the Scremerston Formation. A consequence of the deeping is that the shallow-water strata of the Scremerston and Lower and Middle Limestone formations of the Mid North Sea High passed into deeper-water facies to the south, possibly with bypassing of sand to contemporaneous turbidite settings. This would compare with the spilling of sand across the Craven faults in the Brigantian to give turbidite units such as the Pendleside Sandstone in the Craven Basin as equivalents of Yoredale deltaic strata on the Askrigg Block. Another consequence is that the pre-deepening Cementstones, Fell Sandstone and the earlier parts of the Scremerston Formation may extend as fluvial and deltaic facies beneath the Southern North Sea Basin. This contrasts with what is seen onshore, where these units are mainly restricted to the Northumberland and Stainmore troughs.

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