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

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=== 7.8 Westphalian D (A. tenuis and A. prolifera zones) ===
 
=== 7.8 Westphalian D (A. tenuis and A. prolifera zones) ===
  
Westphalian D strata are not present in many southern North Sea wells. Where rocks of this age have been penetrated, they tend to be characterized by finer-grained lithologies indicative of an increase in accommodation space. However, this is not always the case and, in some wells, thick low-sinuosity channel sandstones are developed. Well 44/27-1 ([[:File:YGS_CHR_06_ASEQ_FIG_07E.jpg|Figure 7E]]) has several of these sandstone units within an interval of over 250 m of inferred Westphalian D age.
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Westphalian D strata are not present in many southern North Sea wells. Where rocks of this age have been penetrated, they tend to be characterized by finer-grained lithologies indicative of an increase in accommodation space. However, this is not always the case and, in some wells, thick low-sinuosity channel sandstones are developed. Well 44/27-1 ([[:File:YGS_CHR_06_ASEQ_FIG_07E.jpg|Figure 7E]]) has several of these sandstone units within an interval of over 250m of inferred Westphalian D age.
  
 
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.

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