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

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== 3. Lithostratigraphy versus sequence stratigraphy ==
 
== 3. Lithostratigraphy versus sequence stratigraphy ==
  
The erection of a standard lithostratigraphical scheme for the Coal Measures is difficult because of the repetition of persistently re-occurring lithologies. On shore, key marine-band markers have been used to subdivide the succession (Stubblefield & Trotter 1957, Ramsbottom et al. 1978, Waters in press; [[:File:YGS_CHR_06_ASEQ_TAB_03.jpg|Table 3]]). The Langsettian–Bolsovian Pennine Coal Measures Group is subdivided into Lower Middle and Upper Coal Measures formations, and is overlain with a diachronous boundary by the red-beds of the Warwickshire Group, Bolsovian–Westphalian D in age. Off shore, in the UK sector of the southern North Sea, the key marine bands cannot be recognized with certainty in many wells, and the onshore scheme is not readily applicable. Thus, the offshore lithostratigraphical scheme of Cameron (1993) was based on lithological criteria rather than on the identification of key marine bands. The Caister Coal Formation includes the sandy strata of Langsettian to earliest Duckmantian age, and very broadly is equivalent to the onshore Lower Coal Measures Formation. The Westoe Coal Formation encompasses rocks of mainly Duckmantian age, and the Schooner Formation includes strata of mainly Bolsovian age, i.e. approximately equivalent to the onshore Middle and Upper Coal Measures formations respectively. The three offshore formations together comprise the Coneybeare Group (Cameron 1993), and their boundaries are locally markedly diachronous. The base of the Group is taken locally at the lowest coal seam in the well, not at an age-constrained or regionally correlatable datum. It locally occurs up to 100 m above the Namurian–Westphalian boundary in wells with good biostratigraphical control. The Westoe Coal Formation is also strongly diachronous at its base, including both Duckmantian and Langsettian strata in the southern area where sandy lithologies cannot be distinguished. A similar situation occurs in the Netherlands sector where the base of the lithologically defined Baarlo Formation can range from intra-Langsettian to intra-Namurian B in age (Van Adrichem Boogaert & Kouwe 1993).
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The erection of a standard lithostratigraphical scheme for the Coal Measures is difficult because of the repetition of persistently re-occurring lithologies. On shore, key marine-band markers have been used to subdivide the succession (Stubblefield & Trotter 1957, Ramsbottom et al. 1978, Waters in press; [[:File:YGS_CHR_06_ASEQ_TAB_03.jpg|Table 3]]). The Langsettian–Bolsovian Pennine Coal Measures Group is subdivided into Lower Middle and Upper Coal Measures formations, and is overlain with a diachronous boundary by the red-beds of the Warwickshire Group, Bolsovian–Westphalian D in age. Off shore, in the UK sector of the southern North Sea, the key marine bands cannot be recognized with certainty in many wells, and the onshore scheme is not readily applicable. Thus, the offshore lithostratigraphical scheme of Cameron (1993) was based on lithological criteria rather than on the identification of key marine bands. The Caister Coal Formation includes the sandy strata of Langsettian to earliest Duckmantian age, and very broadly is equivalent to the onshore Lower Coal Measures Formation. The Westoe Coal Formation encompasses rocks of mainly Duckmantian age, and the Schooner Formation includes strata of mainly Bolsovian age, i.e. approximately equivalent to the onshore Middle and Upper Coal Measures formations respectively. The three offshore formations together comprise the Coneybeare Group (Cameron 1993), and their boundaries are locally markedly diachronous. The base of the Group is taken locally at the lowest coal seam in the well, not at an age-constrained or regionally correlatable datum. It locally occurs up to 100m above the Namurian–Westphalian boundary in wells with good biostratigraphical control. The Westoe Coal Formation is also strongly diachronous at its base, including both Duckmantian and Langsettian strata in the southern area where sandy lithologies cannot be distinguished. A similar situation occurs in the Netherlands sector where the base of the lithologically defined Baarlo Formation can range from intra-Langsettian to intra-Namurian B in age (Van Adrichem Boogaert & Kouwe 1993).
  
 
The lateral continuity of the major coal seams and marine bands between the main Upper Carboniferous basins is well known on shore in the UK, and is likely to continue off shore. Seismic profiles across the offshore basin reveal a consistent lateral continuity of reflectors well below the stage scale, making the highly diachronous lithostratigraphical units of lesser practical application. This invites the application of sequence stratigraphy to well sections with wireline logs and cuttings and cores that can be age constrained by palynology.
 
The lateral continuity of the major coal seams and marine bands between the main Upper Carboniferous basins is well known on shore in the UK, and is likely to continue off shore. Seismic profiles across the offshore basin reveal a consistent lateral continuity of reflectors well below the stage scale, making the highly diachronous lithostratigraphical units of lesser practical application. This invites the application of sequence stratigraphy to well sections with wireline logs and cuttings and cores that can be age constrained by palynology.

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