Editing Dinantian and Namurian depositional systems in the southern North Sea

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The deepest well in the basin probably penetrates only the highest Dinantian strata (Brigantian) and it is therefore impossible to demonstrate when this basin margin developed. It is possible that the early Dinantian saw the shallow-water depositional systems of the block extending southwards without significant change across what is now the basin. Redbeds of latest Devonian or earliest Dinantian age are features of wells onshore and the same sort of extensional subsidence regime probably prevailed offshore at that time. In that case, a phase of intra-Dinantian tectonic activity must have led to the inferred differentiated bathymetry.
 
The deepest well in the basin probably penetrates only the highest Dinantian strata (Brigantian) and it is therefore impossible to demonstrate when this basin margin developed. It is possible that the early Dinantian saw the shallow-water depositional systems of the block extending southwards without significant change across what is now the basin. Redbeds of latest Devonian or earliest Dinantian age are features of wells onshore and the same sort of extensional subsidence regime probably prevailed offshore at that time. In that case, a phase of intra-Dinantian tectonic activity must have led to the inferred differentiated bathymetry.
  
A more precise idea of when this movement took place may come by analogy with wells in and around the Cleveland Basin, Cloughton-1, Kirby Misperton-1 and 41/24-2 [[:File:YGS_CHR_04_DINA_FIG_14.jpg|(Figure 14)]]. In well 41/24-2, the section penetrates into inferred Lower Limestone Formation strata, which appear to have a broadly Yoredale cyclic character. This pattern of deposition persists through the Middle Limestone Formation to the base of the Namurian. In the lowest part of the Namurian, a unit some 50 m thick has very high gamma values and is inferred to be a mudstone with well developed marine bands. This interval is overlain by some 85 m of sandstones, apparently with finer-grained interbeds. The lower part of this interval shows an upwards-coarsening upwards-thickening trend. It is sharply overlain by an upwards-coarsening sequence just over 100 m thick, at the top of which are coarse cross-bedded channel sandstones whose age is thought to be late Pendleian, based on uncorroborated ages indicated on the composite log. The lower sandstones, which are not cored, are thought most likely to be turbidites, with a basin-filling slope progradation above. The succession therefore compares quite closely with the Pendleian fill of the Craven Basin. If the inferred stratigraphical breakdown is correct, the main deepening event at this well would appear to have occurred around the Dinantian/Namurian boundary.
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A more precise idea of when this movement took place may come by analogy with wells in and around the Cleveland Basin, Cloughton-1, Kirby Misperton-1 and 41/24-2 [[:File:YGS_CHR_04_DINA_FIG_14.jpg|(Figure 14)]]. In well 41/24-2, the section penetrates into inferred Lower Limestone Formation strata, which appear to have a broadly Yoredale cyclic character. This pattern of deposition persists through the Middle Limestone Formation to the base of the Namurian. In the lowest part of the Namurian, a unit some 50m thick has very high gamma values and is inferred to be a mudstone with well developed marine bands. This interval is overlain by some 85m of sandstones, apparently with finer-grained interbeds. The lower part of this interval shows an upwards-coarsening upwards-thickening trend. It is sharply overlain by an upwards-coarsening sequence just over 100m thick, at the top of which are coarse cross-bedded channel sandstones whose age is thought to be late Pendleian, based on uncorroborated ages indicated on the composite log. The lower sandstones, which are not cored, are thought most likely to be turbidites, with a basin-filling slope progradation above. The succession therefore compares quite closely with the Pendleian fill of the Craven Basin. If the inferred stratigraphical breakdown is correct, the main deepening event at this well would appear to have occurred around the Dinantian/ Namurian boundary.
  
 
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.

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