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

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Tectonic changes associated with the advancing Variscan Front may have been the principal control on sedimentation in the southern North Sea Westphalian D, lifting the swamps above the level that permitted further marine ingress (Leeder & Hardman 1990; [[:File:YGS_CHR_06_ASEQ_FIG_05.jpg|Figure 5]]). Thick sandstones are likely to be a response to localized tectonic uplift outside the basin rather than to sea-level change. In addition, coals are rare in the ''A. tenuis ''zone in the southern North Sea, although again this is not a universal feature of the Westphalian D elsewhere in northwest Europe (e.g. the Newcastle and Halesowen formations of Staffordshire). The Westphalian D rocks of the southern North Sea tend to be reddened, reflecting a climatic change, associated with the formation of Pangaea, that lead to increasing aridity and an overall oxidizing influence. Associated with this environmental change was the evolutionary appearance of several new palynomorph taxa such as ''Thymospora obscura, T. pseudothiesseni, Cadiospora magna ''and an increase in the occurrence of various striate bisaccate taxa that are the dominant palynoflora of the Permian.
 
Tectonic changes associated with the advancing Variscan Front may have been the principal control on sedimentation in the southern North Sea Westphalian D, lifting the swamps above the level that permitted further marine ingress (Leeder & Hardman 1990; [[:File:YGS_CHR_06_ASEQ_FIG_05.jpg|Figure 5]]). Thick sandstones are likely to be a response to localized tectonic uplift outside the basin rather than to sea-level change. In addition, coals are rare in the ''A. tenuis ''zone in the southern North Sea, although again this is not a universal feature of the Westphalian D elsewhere in northwest Europe (e.g. the Newcastle and Halesowen formations of Staffordshire). The Westphalian D rocks of the southern North Sea tend to be reddened, reflecting a climatic change, associated with the formation of Pangaea, that lead to increasing aridity and an overall oxidizing influence. Associated with this environmental change was the evolutionary appearance of several new palynomorph taxa such as ''Thymospora obscura, T. pseudothiesseni, Cadiospora magna ''and an increase in the occurrence of various striate bisaccate taxa that are the dominant palynoflora of the Permian.
  
The ''A. tenuis ''zone of the southern North Sea is tentatively interpreted as representing a TST in the lower part (4306–4225 m in [[:File:YGS_CHR_06_ASEQ_FIG_07E.jpg|Figure 7E]]), with possible LST and HSTs developed subsequently. An LST may be present in 44/27-1 from 4225–4150 m over an interval of prominent low-sinuosity channel sandstones. The succeeding strata, characterized by alternating crevasse-splay and thin low-sinuosity channel sandstones, up to the Saalian unconformity at 4038 m, are interpreted as an HST. As the lateral extent of some of the Westphalian D sandstone bodies becomes better known, a more refined third-order subdivision of the substage into transgressive, highstand and lowstand systems tracts may be possible. Evidence of fourth-order sea-level fluctuation may be suggested in the redbeds by the interdigitation of, on the one hand, originally grey siderite-bearing strata laid down under poor drainage conditions and, on the other, palaesols indicative of good drainage (Besly et al. 1993). In the view of these latter authors, these alternations are attributable to tectonic causes.
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The ''A. tenuis ''zone of the southern North Sea is tentatively interpreted as representing a TST in the lower part (4306–4225 m in [[:File:YGS_CHR_06_ASEQ_FIG_07E.jpg|Figure 7E]]), with possible LST and HSTs developed subsequently. An LST may be present in 44/27-1 from 4225–4150m over an interval of prominent low-sinuosity channel sandstones. The succeeding strata, characterized by alternating crevasse-splay and thin low-sinuosity channel sandstones, up to the Saalian unconformity at 4038m, are interpreted as an HST. As the lateral extent of some of the Westphalian D sandstone bodies becomes better known, a more refined third-order subdivision of the substage into transgressive, highstand and lowstand systems tracts may be possible. Evidence of fourth-order sea-level fluctuation may be suggested in the redbeds by the interdigitation of, on the one hand, originally grey siderite-bearing strata laid down under poor drainage conditions and, on the other, palaesols indicative of good drainage (Besly et al. 1993). In the view of these latter authors, these alternations are attributable to tectonic causes.
  
 
Strata of the ''A. prolifera ''zone are too poorly preserved or too little known at present off shore to allow the elucidation of sequences. However, considerable thicknesses of strata of this age may be present off shore, possibly containing several third-order systems tracts.
 
Strata of the ''A. prolifera ''zone are too poorly preserved or too little known at present off shore to allow the elucidation of sequences. However, considerable thicknesses of strata of this age may be present off shore, possibly containing several third-order systems tracts.

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