Editing Dinantian and Namurian depositional systems in the southern North Sea

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In the Harton-1 well (Ridd et al. 1970) just south of Tynemouth, equivalents of the main stratigraphical units down to the Scremerston Formation are recognized. A thick-bedded sandstone, whose base is not seen, could be an equivalent of the Fell Sandstone, but is more likely to be a basal sandstone to the Scremerston Formation (Chadwick et al. 1995). Over the Alston Block, the Fell Sandstone thins to zero, illustrating the effects of the concealed Weardale Granite on accommodation space.
 
In the Harton-1 well (Ridd et al. 1970) just south of Tynemouth, equivalents of the main stratigraphical units down to the Scremerston Formation are recognized. A thick-bedded sandstone, whose base is not seen, could be an equivalent of the Fell Sandstone, but is more likely to be a basal sandstone to the Scremerston Formation (Chadwick et al. 1995). Over the Alston Block, the Fell Sandstone thins to zero, illustrating the effects of the concealed Weardale Granite on accommodation space.
  
In contrast, the very deep well, Seal Sands-1, drilled at the mouth of the Tees in an eastern extension of the Stainmore Trough, shows a highly expanded section of equivalent strata. There is no clear-cut equivalent of the Fell Sandstone and it is less easy to split the very thick succession of Yoredale cyclothems into the formations recognized to the north and offshore. The deepest 800 m of the well section are thought likely to be distal fine-grained equivalents of the Fell Sandstone, but there is no proof of this. At Kirby Misperton-1, a sandy section about 300 m thick, may also be a distal equivalent of the Fell Sandstone, although in a different facies. This may be a proximal to distal facies transition similar to that from the Fell Sandstone of Northumberland to the Middle Border Group of Bewcastle along the Northumberland–Solway Trough (Day 1970).
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In contrast, the very deep well, Seal Sands-1, drilled at the mouth of the Tees in an eastern extension of the Stainmore Trough, shows a highly expanded section of equivalent strata. There is no clear-cut equivalent of the Fell Sandstone and it is less easy to split the very thick succession of Yoredale cyclothems into the formations recognized to the north and offshore. The deepest 800m of the well section are thought likely to be distal fine-grained equivalents of the Fell Sandstone, but there is no proof of this. At Kirby Misperton-1, a sandy section about 300m thick, may also be a distal equivalent of the Fell Sandstone, although in a different facies. This may be a proximal to distal facies transition similar to that from the Fell Sandstone of Northumberland to the Middle Border Group of Bewcastle along the Northumberland–Solway Trough (Day 1970).
  
At outcrop, it is clear that the Fell Sandstone is the product of a major sandy braided river system (Turner & Munro 1987). The lateral mobility of the channels led to multi-storey channel units that tended to stack in hanging wall areas of syndepositionally active faults (Turner et al. 1993). Shallow boreholes and detailed mapping show that, in its outcrop area, the unit comprises a series of multi-storey sandbodies separated by mudstone intervals, some of which have marine microfaunas. The combination of low relief, active tectonics and episodic changes in relative sea level probably gave rise to shallow marine flooding of the alluvial tract along the Northumberland–Solway Trough. Across the Mid North Sea High, the depositional regime was probably very similar, with even greater stacking of channel sandbodies across Quadrants 42–43, possibly localized by tectonic control. Differential subsidence, possibly influenced by buried granite plutons, may have influenced this control, but the database is too scattered to demonstrate this. Dominant palaeoflow offshore is thought, on regional grounds, to have been to the south. To the west of the zone of intense channel stacking, higher proportions of finer-grained strata suggest overbank or shallow coastal plains with fewer and smaller channels at well 41/10-1 [[:File:YGS_CHR_04_DINA_FIG_03.jpg|(Figure 3)]], [[:File:YGS_CHR_04_DINA_FIG_06.jpg|(Figure 6)]]. This change takes place over a data gap of some 60 km and it quite possible that migration of the larger river channels to the west was blocked by tectonically controlled topography, as implied by Maynard & Dunay (1999), who suggested that faulting was the prime control. It seems equally possible that well 41/10-1 is drilled in a depositional shadow zone of a granite-cored block, with or without associated faulting [[:File:YGS_CHR_04_DINA_FIG_06.jpg|(Figure 6)]]. The thick finer-grained succession at 41/10-1 includes limestones and thin coal seams, and compares with the overlying Scremerston Formation; on lithostratigraphic grounds it should be included in that formation. However, thickness criteria suggest that it was deposited at a time when thick multi-storey channel sandstone units of the typical Fell Sandstone were being deposited along strike. Picking an equivalent of the top of the Fell Sandstone in the expanded Scremerston Formation in this well is somewhat arbitrary.
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At outcrop, it is clear that the Fell Sandstone is the product of a major sandy braided river system (Turner & Munro 1987). The lateral mobility of the channels led to multi-storey channel units that tended to stack in hanging wall areas of syndepositionally active faults (Turner et al. 1993). Shallow boreholes and detailed mapping show that, in its outcrop area, the unit comprises a series of multi-storey sandbodies separated by mudstone intervals, some of which have marine microfaunas. The combination of low relief, active tectonics and episodic changes in relative sea level probably gave rise to shallow marine flooding of the alluvial tract along the Northumberland–Solway Trough. Across the Mid North Sea High, the depositional regime was probably very similar, with even greater stacking of channel sandbodies across Quadrants 42–43, possibly localized by tectonic control. Differential subsidence, possibly influenced by buried granite plutons, may have influenced this control, but the database is too scattered to demonstrate this. Dominant palaeoflow offshore is thought, on regional grounds, to have been to the south. To the west of the zone of intense channel stacking, higher proportions of finer-grained strata suggest overbank or shallow coastal plains with fewer and smaller channels at well 41/10-1 [[:File:YGS_CHR_04_DINA_FIG_03.jpg|(Figure 3)]], [[:File:YGS_CHR_04_DINA_FIG_06.jpg|(Figure 6)]]. This change takes place over a data gap of some 60km and it quite possible that migration of the larger river channels to the west was blocked by tectonically controlled topography, as implied by Maynard & Dunay (1999), who suggested that faulting was the prime control. It seems equally possible that well 41/10-1 is drilled in a depositional shadow zone of a granite-cored block, with or without associated faulting [[:File:YGS_CHR_04_DINA_FIG_06.jpg|(Figure 6)]]. The thick finer-grained succession at 41/10-1 includes limestones and thin coal seams, and compares with the overlying Scremerston Formation; on lithostratigraphic grounds it should be included in that formation. However, thickness criteria suggest that it was deposited at a time when thick multi-storey channel sandstone units of the typical Fell Sandstone were being deposited along strike. Picking an equivalent of the top of the Fell Sandstone in the expanded Scremerston Formation in this well is somewhat arbitrary.
  
 
To the south, distal equivalents of the Fell Sandstone are unknown offshore. It is possible that continuing extension had started to create a deep basin with a well defined northern margin by this time. Fluvial sand could then have been bypassed to deeper water. On the other hand, more gradual subsidence may have created a gently inclined ramp across which deltas prograded. The succession in the Kirby Misperton-1 well can be interpreted as a possible marine equivalent but of unknown water depth. Such a transition, if correct, would compare with the increasing marine influence seen in the Fell Sandstone equivalents as they are traced down current to the southwest along the Northumberland–Solway Trough. Alternatively, they may represent a deeper-water facies. Either way, they need not provide an analogue to the depositional system that existed offshore.
 
To the south, distal equivalents of the Fell Sandstone are unknown offshore. It is possible that continuing extension had started to create a deep basin with a well defined northern margin by this time. Fluvial sand could then have been bypassed to deeper water. On the other hand, more gradual subsidence may have created a gently inclined ramp across which deltas prograded. The succession in the Kirby Misperton-1 well can be interpreted as a possible marine equivalent but of unknown water depth. Such a transition, if correct, would compare with the increasing marine influence seen in the Fell Sandstone equivalents as they are traced down current to the southwest along the Northumberland–Solway Trough. Alternatively, they may represent a deeper-water facies. Either way, they need not provide an analogue to the depositional system that existed offshore.

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