Editing Dinantian and Namurian depositional systems in the southern North Sea

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This unit, of late Asbian age, is extensively penetrated by wells offshore. It is distinguished from the Scremerston Formation by a lower incidence of coal seams and by a much clearer pattern of upwards-coarsening cyclothems with limestones at their bases, features typical of a Yoredale facies [[:File:YGS_CHR_04_DINA_FIG_03.jpg|(Figure 3)]]. It is the earliest Carboniferous unit in which palaeovalleys, infilled by thick multistorey channel sandstones, are known to be developed [[:File:YGS_CHR_04_DINA_FIG_08.jpg|(Figure 8)]]. Large multi-storey channel units are also conspicuous at outcrop on the Northumberland coast (Gardiner 1984). The incoming of both clear cyclicity and incision may relate to an increasing eustatic control on sea level, driven by the onset of continental glaciation in the Southern Hemisphere.
 
This unit, of late Asbian age, is extensively penetrated by wells offshore. It is distinguished from the Scremerston Formation by a lower incidence of coal seams and by a much clearer pattern of upwards-coarsening cyclothems with limestones at their bases, features typical of a Yoredale facies [[:File:YGS_CHR_04_DINA_FIG_03.jpg|(Figure 3)]]. It is the earliest Carboniferous unit in which palaeovalleys, infilled by thick multistorey channel sandstones, are known to be developed [[:File:YGS_CHR_04_DINA_FIG_08.jpg|(Figure 8)]]. Large multi-storey channel units are also conspicuous at outcrop on the Northumberland coast (Gardiner 1984). The incoming of both clear cyclicity and incision may relate to an increasing eustatic control on sea level, driven by the onset of continental glaciation in the Southern Hemisphere.
  
One inferred palaeovalley sandstone in well 42/10-2 is the reservoir for a gas discovery and has been named the Whitby Member ([[:File:YGS_CHR_04_DINA_FIG_08.jpg|(Figure 8)]]; Maynard & Dunay 1999). Interpreted borehole image logs from that sandstone suggest cross bedding directed to the south. Maynard & Dunay (1999) suggested on the basis of similar log signatures that this sandstone could be correlated over an east–west distance of some 50 km to well 41/10-1; but, as the wells in question lie normal to the palaeoflow, it seems more likely that the log similarities are fortuitous. The southern limit of deltaic progradation is poorly constrained, as there are no certain penetrations of stratigraphical equivalents in the basin. This was a time when deepening of the Southern North Sea Basin may have started and so periods of low-stand incision could have coincided with the bypassing of sand to distal deepwater areas.
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One inferred palaeovalley sandstone in well 42/10-2 is the reservoir for a gas discovery and has been named the Whitby Member ([[:File:YGS_CHR_04_DINA_FIG_08.jpg|(Figure 8)]]; Maynard & Dunay 1999). Interpreted borehole image logs from that sandstone suggest cross bedding directed to the south. Maynard & Dunay (1999) suggested on the basis of similar log signatures that this sandstone could be correlated over an east–west distance of some 50km to well 41/10-1; but, as the wells in question lie normal to the palaeoflow, it seems more likely that the log similarities are fortuitous. The southern limit of deltaic progradation is poorly constrained, as there are no certain penetrations of stratigraphical equivalents in the basin. This was a time when deepening of the Southern North Sea Basin may have started and so periods of low-stand incision could have coincided with the bypassing of sand to distal deepwater areas.
  
Thickness changes in the Lower Limestone Formation are quite small across most of the offshore area, with about 200 m being typical. Only at Harton-1, on the fringes of the Alston Block, and at Seal Sands-1, is the unit respectively thinner and thicker. The differences in thicknesses, and the fact that the Alston Block was flooded at this time, suggest diminishing differential subsidence. Also, the offshore area is considerably more sand rich than the equivalent intervals in the onshore Harton-1 and Seal Sands-1 wells, where limestones are much more important. The interval extends southwards in a Yoredale facies at least as far as well 41/24a-2, offshore from Scarborough. However, at Kirby Misperton-1 a relatively sand-free section some 300 m thick seems a likely correlative, although lack of robust biostratigraphy makes for uncertainty. The section at Kirby Misperton-1 is possibly in a slope or deepwater facies.
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Thickness changes in the Lower Limestone Formation are quite small across most of the offshore area, with about 200m being typical. Only at Harton-1, on the fringes of the Alston Block, and at Seal Sands-1, is the unit respectively thinner and thicker. The differences in thicknesses, and the fact that the Alston Block was flooded at this time, suggest diminishing differential subsidence. Also, the offshore area is considerably more sand rich than the equivalent intervals in the onshore Harton-1 and Seal Sands-1 wells, where limestones are much more important. The interval extends southwards in a Yoredale facies at least as far as well 41/24a-2, offshore from Scarborough. However, at Kirby Misperton-1 a relatively sand-free section some 300m thick seems a likely correlative, although lack of robust biostratigraphy makes for uncertainty. The section at Kirby Misperton-1 is possibly in a slope or deepwater facies.
  
 
==== 3.1.5 The Middle Limestone Formation ====
 
==== 3.1.5 The Middle Limestone Formation ====

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