Editing A sequence-stratigraphy scheme of the Late Carboniferous, southern North Sea, Anglo-Dutch sector

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There is a generalized north to south decrease in sandstone, e.g. the thick sandstones within the ''A. lenisulcata ''and ''C. communis ''zone recognizable in 44/22-1 and 44/23-4, and in the ''C. communis ''zone in K1-02, are hardly evident in well P/10-1. The sandstone-dominated interval of the upper ''A. modiolaris ''zone HST–LST (Caister–Murdoch sandstone play of Quadrant 44) diminishes in prominence farther south into quadrants 49 (49/1-3) and 53 (53/10-1). This southward reduction in Early Duckmantian sandstone development continues into The Netherlands quadrant P (P10-1 and P13-1). Associated with it, the “coal-break” upper boundary of this unit with the overlying ''L. similis-pulchra ''zone is clear in quadrants 44, 49 and K, but much less so in quadrants 53 and P.
 
There is a generalized north to south decrease in sandstone, e.g. the thick sandstones within the ''A. lenisulcata ''and ''C. communis ''zone recognizable in 44/22-1 and 44/23-4, and in the ''C. communis ''zone in K1-02, are hardly evident in well P/10-1. The sandstone-dominated interval of the upper ''A. modiolaris ''zone HST–LST (Caister–Murdoch sandstone play of Quadrant 44) diminishes in prominence farther south into quadrants 49 (49/1-3) and 53 (53/10-1). This southward reduction in Early Duckmantian sandstone development continues into The Netherlands quadrant P (P10-1 and P13-1). Associated with it, the “coal-break” upper boundary of this unit with the overlying ''L. similis-pulchra ''zone is clear in quadrants 44, 49 and K, but much less so in quadrants 53 and P.
  
Converse to this reduction in net sandstone development, there is an increase in overall thickness of the mudstone-dominated ''L. similis-pulchra ''zone TST southwards, from Quadrant 44 through 49 and into Quadrant P. The base Permian unconformity truncates this interval in K1-02, P10-1 and P13-1, but P13-1 still has a greater thickness of this interval than 44/27-1. This trend may reflect a southward decrease in the development of alluvial channels within this TST that may have significantly reduced this interval thickness in quadrants 44 and 49. The upper Bolsovian, ''A. phillipsii ''zone, LST sandstone unit is clearly developed above a prominent ''c. ''20 m basal sandstone body in quadrants 44 and 49. Farther south, however, these strata have been eroded away at the base Permian unconformity.
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Converse to this reduction in net sandstone development, there is an increase in overall thickness of the mudstonedominated ''L. similis-pulchra ''zone TST southwards, from Quadrant 44 through 49 and into Quadrant P. The base Permian unconformity truncates this interval in K1-02, P10-1 and P13-1, but P13-1 still has a greater thickness of this interval than 44/27-1. This trend may reflect a southward decrease in the development of alluvial channels within this TST that may have significantly reduced this interval thickness in quadrants 44 and 49. The upper Bolsovian, ''A. phillipsii ''zone, LST sandstone unit is clearly developed above a prominent ''c. ''20m basal sandstone body in quadrants 44 and 49. Farther south, however, these strata have been eroded away at the base Permian unconformity.
  
 
These trends in the sandstone development of the LSTs reflect increasing distance from the northerly sediment source. During periods of HST and TST, with more numerous marine incursions, topographically lower regions in the south of the basin would be flooded first and to greater water depths. There would have been a general northward shallowing in depth of flooding, together with a reduction in salinity towards some areas of peatswamp coal deposition that avoided flooding. Between flooding events, areas of forested peat swamps would be coeval with more continuously waterlogged areas farther south and more areas occupied by lakes.
 
These trends in the sandstone development of the LSTs reflect increasing distance from the northerly sediment source. During periods of HST and TST, with more numerous marine incursions, topographically lower regions in the south of the basin would be flooded first and to greater water depths. There would have been a general northward shallowing in depth of flooding, together with a reduction in salinity towards some areas of peatswamp coal deposition that avoided flooding. Between flooding events, areas of forested peat swamps would be coeval with more continuously waterlogged areas farther south and more areas occupied by lakes.

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