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

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Following the deposition of the Vanderbeckei Marine Band, a reduced rate of sea-level rise, followed by a rapid fall in base level, caused a reduction in the rate of formation of accommodation space and markedly increased (low- and high-sinuosity) channel sandstone sedimentation. Evidence of incision, erosion and reworking over this zone is provided by the occurrence of reworked Langsettian spores, and rarer Namurian spores. Some more sandstone-prone wells may yield consistent occurrences of ''Radiizonates aligerens ''from this interval, a Langsettian marker, some 100 m and more above the base of the Duckmantian. In other instances the coarse sandstone units yield only very poor palynomorph assemblages, because of the high energy of deposition. Incision during sandstone deposition may have removed a large interval of highstand strata deposited immediately above the preceding marine band.
 
Following the deposition of the Vanderbeckei Marine Band, a reduced rate of sea-level rise, followed by a rapid fall in base level, caused a reduction in the rate of formation of accommodation space and markedly increased (low- and high-sinuosity) channel sandstone sedimentation. Evidence of incision, erosion and reworking over this zone is provided by the occurrence of reworked Langsettian spores, and rarer Namurian spores. Some more sandstone-prone wells may yield consistent occurrences of ''Radiizonates aligerens ''from this interval, a Langsettian marker, some 100 m and more above the base of the Duckmantian. In other instances the coarse sandstone units yield only very poor palynomorph assemblages, because of the high energy of deposition. Incision during sandstone deposition may have removed a large interval of highstand strata deposited immediately above the preceding marine band.
  
The spore ''Crassispora kosankei ''is prominent in this zone, commonly occurring in very great abundance. This is in keeping with the alluvial swamp depositional environment that has been associated with this arborescent lycopod spore. This can be compared with its abundance in the previous ''C. communis ''LST, although in the latter it is less prominent than here in the Early Duckmantian. ''Laevigatosporites ''spp. are, like the ''C. communis ''zone, also in abundance within the Upper ''A. modiolaris ''zone, reflecting the waterlogged ephemeral depositional environment. Another spore taxon that is prominent within this zone and the ''C. communis ''zone is ''Vestispora costata'', which may, like ''C. kosankei, ''come from a plant that favoured an environment of alluvial swamps and levee depositional environments. The important Duckmantian and younger palynological marker taxa ''Endosporites globiformis ''and ''Dictyotriletes bireticulatus ''make their appearance within this zone.
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The spore ''Crassispora kosankei ''is prominent in this zone, commonly occurring in very great abundance. This is in keeping with the alluvial swamp depositional environment that has been associated with this arborescent lycopod spore. This can be compared with its abundance in the previous ''C. communis ''LST, although in the latter it is less prominent than here in the Early Duckmantian. ''Laevigatosporites ''spp. are, like the ''C. communis ''zone, also in abundance within the Upper ''A. modiolaris ''zone, reflecting the waterlogged ephemeral depositional environment. Another spore taxon that is prominent within this zone and the ''C. communis ''zone is ''Vestispora costata'', which may, like
  
=== 7.5 Late Duckmantian (L. ''similis-pulchra'' zone) ===
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''C. kosankei, ''come from a plant that favoured an environment of alluvial swamps and levee depositional environments. The important Duckmantian and younger palynological marker taxa ''Endosporites globiformis ''and ''Dictyotriletes bireticulatus ''make their appearance within this zone.
  
The base of the Late Duckmantian is taken at the Barnsley (Top Hard) Coal, coincident with a marked seismic break that is inferred to be the initial flooding surface heralding the renewed onset of marine transgression. This zone shows a return to the dominance of argillaceous lithotypes (facies association B), and is interpreted as a TST. The zone is dominated by alternating crevasse-splay mudstone–siltstone units and coal swamp and lacustrine mudstones ([[:File:YGS_CHR_06_ASEQ_FIG_06E.jpg|Figure 6E]], [[:File:YGS_CHR_06_ASEQ_FIG_07B.jpg|Figure 7B]]). Its thickness in 44/27-1 is 258 m.
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=== 7.5 Late Duckmantian (L. similis-pulchra zone) ===
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The base of the Late Duckmantian is taken at the Barnsley (Top Hard) Coal, coincident with a marked seismic break that is inferred to be the initial flooding surface heralding the renewed onset of marine transgression. This zone shows a return to the dominance of argillaceous lithotypes (facies association B), and is interpreted as a TST. The zone is dominated by alternating crevasse-splay mudstone–siltstone units and coal swamp and lacustrine mudstones ([[:File:YGS_CHR_06_ASEQ_FIG_06E.jpg|Figure 6E]], [[:File:YGS_CHR_06_ASEQ_FIG_07B.jpg|Figure 7B]]). Its thickness in 44/27-1 is 258m.
  
 
The zone contains several coal seams in the lower part and several marine bands in its upper part. Intervals containing low-sinuosity sandstones are locally developed in places (more so in 44/22-1 than 44/27-1 – Figure 6e). Flooding surfaces near the top of the zone are indicated in the East Midlands by the Two Foot, Clowne, Haughton and Sutton marine bands. This transgressive sequence is terminated by the MFS of the Aegiranum (Mansfield) Marine Band, which marks the Westphalian B/C boundary.
 
The zone contains several coal seams in the lower part and several marine bands in its upper part. Intervals containing low-sinuosity sandstones are locally developed in places (more so in 44/22-1 than 44/27-1 – Figure 6e). Flooding surfaces near the top of the zone are indicated in the East Midlands by the Two Foot, Clowne, Haughton and Sutton marine bands. This transgressive sequence is terminated by the MFS of the Aegiranum (Mansfield) Marine Band, which marks the Westphalian B/C boundary.
  
This zone yields palynological assemblages overwhelmingly dominated by lycospores, although this cannot be considered to be diagnostic of the zone, as such spores are ubiquitous throughout the Coal Measures. However, they are accompanied by a consistent prominence of ''Densosporites ''spp. that reflects the major development of mature coal seams within this zone. The zone is also characterized by the evolutionary appearance of taxa that may be associated with large areas of persistent peat swamps; these include ''Vestispora pseudoreticulata, Punctatisporites granifer, Triquitrites ''spp., ''Perotriletes perinatus ''and ''Cristatisporites solaris.''
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This zone yields palynological assemblages overwhelmingly dominated by lycospores, although this cannot be considered to be diagnostic of the zone, as such spores are ubiquitous throughout the Coal Measures. However, they are accompanied by a consistent prominence of ''Densosporites ''spp. that reflects the major development of mature coal seams within this zone. The
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zone is also characterized by the evolutionary appearance of taxa that may be associated with large areas of persistent peat swamps; these include ''Vestispora pseudoreticulata, Punctatisporites granifer, Triquitrites ''spp., ''Perotriletes perinatus ''and ''Cristatisporites solaris.''
  
 
Certain other taxa may not have been able to survive the demise of these very extensive and persistent settled swamp environments. This may have been associated with a decline in the rate of sea-level rise, and the sedimentation rate may have begun to exceed subsidence rates. Various taxa became extinct at the top of this zone, including ''Raistrickia fulva, ''abundant ''Dictyotriletes bireticulatus ''and ''Camptotriletes bucculentus.''
 
Certain other taxa may not have been able to survive the demise of these very extensive and persistent settled swamp environments. This may have been associated with a decline in the rate of sea-level rise, and the sedimentation rate may have begun to exceed subsidence rates. Various taxa became extinct at the top of this zone, including ''Raistrickia fulva, ''abundant ''Dictyotriletes bireticulatus ''and ''Camptotriletes bucculentus.''

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