Editing Carboniferous miospore biostratigraphy of the North Sea

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[[File:YGS_CHR_02_CARB_FIG_06.jpg|thumbnail|Figure 6 Correlation of the North Sea Westphalian miospore biozones with the UK sector lithostratigraphy. No vertical scale implied.]]
 
[[File:YGS_CHR_02_CARB_FIG_06.jpg|thumbnail|Figure 6 Correlation of the North Sea Westphalian miospore biozones with the UK sector lithostratigraphy. No vertical scale implied.]]
  
'''By D. McLean, B. Owens, R. Neves'''
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== Carboniferous miospore biostratigraphy of the North Sea ==
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By D. McLean, B. Owens, R. Neves
  
 
From: Pages 13–24 of ''Carboniferous hydrocarbon geology: the southern North Sea and surrounding onshore areas'', edited by J. D. Collinson, D. J. Evans, D. W. Holliday, N. S. Jones. Published as volume 7 in the Occasional Publications series of the Yorkshire Geological Society, © Yorkshire Geological Society 2005.
 
From: Pages 13–24 of ''Carboniferous hydrocarbon geology: the southern North Sea and surrounding onshore areas'', edited by J. D. Collinson, D. J. Evans, D. W. Holliday, N. S. Jones. Published as volume 7 in the Occasional Publications series of the Yorkshire Geological Society, © Yorkshire Geological Society 2005.
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== Introduction ==
 
== Introduction ==
  
Biostratigraphic correlation of the European Carboniferous at outcrop and in cored boreholes conventionally relies upon ammonoids, brachiopods, corals, non-marine bivalves and macrofloras. Foraminifera, conodonts and palynomorphs are also important in correlating Early Carboniferous strata (George et al. 1976, Riley 1993), although the foraminifera and conodonts are of less value in correlating Late Carboniferous strata. Here, much of the marine macrofauna (bivalves, brachiopods, crinoids, fish, gastropods, ichnofaunas) may possess no intrinsic stratigraphical value, but, in the absence of ammonoids, can be used as proxy indicators of stratigraphically significant marine bands (Calver 1968, Goosens et al. 1974). In drilling for hydrocarbons, the scarcity of coherent rock material (cores and side-wall cores) generally limits the use of biostratigraphy based upon conventional macrofossils. Fragmentary ditch cuttings provide the standard type of subsurface sample material off shore, and so biostratigraphy is reliant upon the smaller microfossil groups. Foraminifera and ostracods may be extracted from ditch cuttings, but conodonts are too large to be preserved whole within such samples. Further, these fossil types occur in such limited concentrations, or in stratigraphically limited intervals (e.g. Late Carboniferous marine bands), as to make their study impracticable. In the Carboniferous of the North Sea the onus falls upon microscopic plant remains (miospores) to provide biostratigraphic subdivision and correlation (McLean & Murray 1996, Maynard et al. 1997). Miospores are generally well preserved and abundant in non-marine and non-carbonate marine facies. They may be present in carbonate and redbed sequences, but are usually less diverse and less well preserved.
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Biostratigraphic correlation of the European Carboniferous at outcrop and in cored boreholes conventionally relies upon ammonoids, brachiopods, corals, non-marine bivalves and macrofloras. Foraminifera, conodonts and palynomorphs are also important in correlating Early Carboniferous strata (George et al. 1976, Riley 1993), although the foraminifera and conodonts are of less value in correlating Late Carboniferous strata. Here, much of the marine macrofauna (bivalves, brachiopods, crinoids, fish, gastropods, ichnofaunas) may possess no intrinsic stratigraphical value, but, in the absence of ammonoids, can be used as proxy indicators of stratigraphically significant marine bands (Calver 1968, Goosens et al. 1974). In drilling for hydrocarbons, the scarcity of coherent rock material (cores and side-wall cores) generally limits the use of biostratigraphy based upon conventional macrofossils. Fragmentary ditch cuttings provide the standard type of subsurface sample material off shore, and so biostratigraphy is reliant upon the smaller micro-fossil groups. Foraminifera and ostracods may be extracted from ditch cuttings, but conodonts are too large to be preserved whole within such samples. Further, these fossil types occur in such limited concentrations, or in stratigraphically limited intervals (e.g. Late Carboniferous marine bands), as to make their study impracticable. In the Carboniferous of the North Sea the onus falls upon microscopic plant remains (miospores) to provide biostratigraphic subdivision and correlation (McLean & Murray 1996, Maynard et al. 1997). Miospores are generally well preserved and abundant in non-marine and non-carbonate marine facies. They may be present in carbonate and redbed sequences, but are usually less diverse and less well preserved.
  
 
In the literature on North Sea Carboniferous exploration there are only two studies in which macrofaunal biostratigraphy is described. The identification of ammonoids recovered from targeted rotary sidewall cores by Riley (in O’Mara et al. 1999) allowed the recognition of several Marsdenian to early Langsettian marine bands in the Trent field. Interwell correlation of these horizons provided the framework for a sedimentary sequence stratigraphy of the reservoir interval of the field.
 
In the literature on North Sea Carboniferous exploration there are only two studies in which macrofaunal biostratigraphy is described. The identification of ammonoids recovered from targeted rotary sidewall cores by Riley (in O’Mara et al. 1999) allowed the recognition of several Marsdenian to early Langsettian marine bands in the Trent field. Interwell correlation of these horizons provided the framework for a sedimentary sequence stratigraphy of the reservoir interval of the field.
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To date there are only two miospore biozonation schemes in the public domain specific to the North Sea Carboniferous. The scheme for the Westphalian by McLean (1995a) is an early draft of that presented here for the same interval. The biozones described for the whole Carboniferous by Maynard et al. (1997) are vaguely defined and of limited stratigraphical resolution ([[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]).
 
To date there are only two miospore biozonation schemes in the public domain specific to the North Sea Carboniferous. The scheme for the Westphalian by McLean (1995a) is an early draft of that presented here for the same interval. The biozones described for the whole Carboniferous by Maynard et al. (1997) are vaguely defined and of limited stratigraphical resolution ([[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]).
  
Accumulation of palynostratigraphical data over the past 30 years and more has allowed the development of a miospore biozonation scheme specific to the North Sea. This is based upon the synthesis of data from more than 13000 productive palynological samples from more than 300 Carboniferous well sections. The biozonation includes data from both coal seams and mudstone/siltstone lithologies. The fact that different lithologies and facies yield different palynological assemblages (both of miospore taxa and total organic debris) is well known (Neves 1958) and provides the basis for high-resolution palynofacies studies (e.g. for the Westphalian of the Caister field by Ritchie & Pratsides 1993, and for the late Westphalian onshore Netherlands by Van de Laar & Van der Zwan 1996). It is also recognized that the stratigraphical ranges of most, if not all, miospore taxa seen in coal seams are shorter than their ranges in clastic strata. Consequently, the best palynological dataset includes assemblages from all lithological types. The biozonation is homotaxial (''sensu ''Scott 1965) in approach (i.e. it is based upon the relative order of appearances and disappearances of taxa), but remains comparable to the framework provided by the onshore zonations. The onshore biozones were consciously defined to reflect the evolution of the Carboniferous microflora. As such, their bases are principally defined by the first appearances of certain morphologically distinctive and stratigraphically restricted taxa. However, because of the scarcity of cored sections in the North Sea, the offshore biozones are defined, where possible, on the last stratigraphical occurrences (range tops or first downhole appearances) of zonal taxa. This method makes the biozones applicable to ditch cuttings material. Selection of zonal taxa is based upon the consistent occurrence of the range top or base of each taxon in several well sections. Consequently, several relatively common taxa, which, given their representation in onshore biozones would be expected to be stratigraphically significant, have proved not to be (at least within the limitations of the database). For example, the intra-Namurian range top of the highly distinctive form ''Ibrahimispores magnificus ''occurs at inconsistent levels with respect to certain other taxa taken as standards, and so is excluded as a significant biostratigraphical event. The range base of ''Cadiospora magna ''(traditionally considered to be a Westphalian D marker taxon, e.g. Smith & Butterworth 1967, Maynard et al. 1997) occurs irregularly in the mid- and early Bolsovian of the North Sea UK sector. Other taxa (e.g. ''Fragilipollenites radiatus ''and ''Pteroretis primum''), although morphologically distinctive, occur so rarely as to preclude the recognition of consistent range limits. On the other hand, some taxa, particularly in the late Namurian (e.g. ''Ahrensisporites beeleyensis, Alatisporites nudus ''and ''Triquitrites nodosus'') are rare but have consistent stratigraphical limits, and so are considered significant.
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Accumulation of palynostratigraphical data over the past 30 years and more has allowed the development of a miospore biozonation scheme specific to the North Sea. This is based upon the synthesis of data from more than 13000 productive palynological samples from more than 300 Carboniferous well sections. The biozonation includes data from both coal seams and mudstone/siltstone lithologies. The fact that different lithologies and facies yield different palynological assemblages (both of miospore taxa and total organic debris) is well known (Neves 1958) and provides the basis for high-resolution palynofacies studies (e.g. for the Westphalian of the Caister field by Ritchie & Pratsides 1993, and for the late Westphalian onshore Netherlands by Van de Laar & Van der Zwan 1996). It is also recognized that the stratigraphical ranges of most, if not all, miospore taxa seen in coal seams are shorter than their ranges in clastic strata. Consequently, the best palynological dataset includes assemblages from all lithological types. The biozonation is homotaxial (''sensu ''Scott 1965) in approach (i.e. it is based upon the relative order of appearances and disappearances of taxa), but remains comparable to the framework provided by the onshore zonations. The onshore biozones were consciously defined to reflect the evolution of the Carboniferous microflora. As such, their bases are principally defined by the first appearances of certain morphologically distinctive and stratigraphically restricted taxa. However, because of the scarcity of cored sections in the North Sea, the offshore biozones are defined, where possible, on the last stratigraphical occurrences (range tops or first downhole appearances) of zonal taxa. This method makes the biozones applicable to ditch cuttings material. Selection of zonal taxa is based upon the consistent occurrence of the range top or base of each taxon in several well sections. Consequently, several relatively common taxa, which, given their representation in onshore biozones would be expected to be stratigraphically significant, have proved not to be (at least within the limitations of the database). For example, the intraNamurian range top of the highly distinctive form ''Ibrahimispores magnificus ''occurs at inconsistent levels with respect to certain other taxa taken as standards, and so is excluded as a significant biostratigraphical event. The range base of ''Cadiospora magna ''(traditionally considered to be a Westphalian D marker taxon, e.g. Smith & Butterworth 1967, Maynard et al. 1997) occurs irregularly in the mid- and early Bolsovian of the North Sea UK sector. Other taxa (e.g. ''Fragilipollenites radiatus ''and ''Pteroretis primum''), although morphologically distinctive, occur so rarely as to preclude the recognition of consistent range limits. On the other hand, some taxa, particularly in the late Namurian (e.g. ''Ahrensisporites beeleyensis, Alatisporites nudus ''and ''Triquitrites nodosus'') are rare but have consistent stratigraphical limits, and so are considered significant.
  
 
Definitions of the Dinantian, Namurian and Westphalian biozones are shown on [[:File:YGS_CHR_02_CARB_FIG_02.jpg|Figure 2]], [[:File:YGS_CHR_02_CARB_FIG_03.jpg|Figure 3]], [[:File:YGS_CHR_02_CARB_FIG_04.jpg|Figure 4]] respectively. Full citations for all taxa are given in the Appendix. Individual biozones are defined by the range top or base of a particular miospore taxon and represent interval or partial-range biozones. As such, they differ from the standard approach to Carboniferous palynostratigraphy, where assemblage biozones (Smith & Butterworth 1967) or concurrent range biozones (Neves et al. 1972, 1973, Clayton et al. 1977, Owens et al. 1977) have traditionally been used. It is recognized that any one defining taxon will not always be represented in a section. So, some associated taxa whose range tops or bases are known to occur ''in proximity to ''that of the defining taxon are also indicated.
 
Definitions of the Dinantian, Namurian and Westphalian biozones are shown on [[:File:YGS_CHR_02_CARB_FIG_02.jpg|Figure 2]], [[:File:YGS_CHR_02_CARB_FIG_03.jpg|Figure 3]], [[:File:YGS_CHR_02_CARB_FIG_04.jpg|Figure 4]] respectively. Full citations for all taxa are given in the Appendix. Individual biozones are defined by the range top or base of a particular miospore taxon and represent interval or partial-range biozones. As such, they differ from the standard approach to Carboniferous palynostratigraphy, where assemblage biozones (Smith & Butterworth 1967) or concurrent range biozones (Neves et al. 1972, 1973, Clayton et al. 1977, Owens et al. 1977) have traditionally been used. It is recognized that any one defining taxon will not always be represented in a section. So, some associated taxa whose range tops or bases are known to occur ''in proximity to ''that of the defining taxon are also indicated.
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Nomenclature of the biozones is made for ease of use and it avoids the binomial system usual for onshore Carboniferous miospore biozones. The bases of most of the North Sea biozones are defined by stratigraphical range tops, with the defining taxa occurring in the biozone below that which they define. As this may lead to some confusion, the biozones here are not named after miospore taxa, as is conventional, but are numbered sequentially. Standard practice determines that type sections need not be defined for biozones (Hedberg 1976) and these are not designated here. However, the North Sea biozones will be incorporated into a major review of European Carboniferous palynostratigraphy. Standard sections for pan-northwest European biozones will be provided in this new scheme (Clayton et al. 2003).
 
Nomenclature of the biozones is made for ease of use and it avoids the binomial system usual for onshore Carboniferous miospore biozones. The bases of most of the North Sea biozones are defined by stratigraphical range tops, with the defining taxa occurring in the biozone below that which they define. As this may lead to some confusion, the biozones here are not named after miospore taxa, as is conventional, but are numbered sequentially. Standard practice determines that type sections need not be defined for biozones (Hedberg 1976) and these are not designated here. However, the North Sea biozones will be incorporated into a major review of European Carboniferous palynostratigraphy. Standard sections for pan-northwest European biozones will be provided in this new scheme (Clayton et al. 2003).
  
Work by one author (DM) has allowed the recognition of limited and scattered independent (macropalaeontological) control points in cored sections, which provide some calibration of the palynological zonation. Miospore biozones have been determined for the whole of the Carboniferous that occurs in the northern and southern parts of the North Sea ([[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]), but the level of stratigraphical resolution of these is variable. To a large extent, stratigraphical resolution is determined by the number of well sections available for study reflecting the stratigraphical distribution of hydrocarbon targets and economic reservoirs. Most of the data are clustered in Westphalian strata (in the northern part of the Southern North Sea Basin ([[:File:YGS_CHR_02_CARB_FIG_05.jpg|Figure 5]]), with lesser amounts in mid- to late Dinantian strata (in the Outer Moray Firth Basin). Data from the Namurian are sufficient to allow a refined and robust biozonation, although data from the pre-Holkerian are provided by only a few well sections, mostly around the margins of the offshore Carboniferous basins. Palynostratigraphy of these older strata is further limited by the existence of Tournaisian sandstone-rich redbed facies (Buchan Formation of Cameron 1993a) which are commonly barren.
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Work by one author (DM) has allowed the recognition of limited and scattered independent (macropalaeontological) control points in cored sections, which provide some calibration of the palynological zonation. Miospore biozones have been determined for the whole of the Carboniferous that occurs in the northern and southern parts of the North Sea ([[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]), but the level of stratigraphical resolution of these is variable. To a large extent, stratigraphical resolution is determined by the number of well sections available for study reflecting the stratigraphical distribution of hydrocarbon targets and economic reservoirs. Most of the data are clustered in Westphalian strata (in the northern part of the Southern North Sea Basin ([[:File:YGS_CHR_02_CARB_FIG_05.jpg|Figure 5]]), with lesser amounts in mid- to late Dinantian strata (in the Outer Moray Firth Basin). Data from the Namurian are sufficient to allow a refined and robust biozonation, although data from the preHolkerian are provided by only a few well sections, mostly around the margins of the offshore Carboniferous basins. Palynostratigraphy of these older strata is further limited by the existence of Tournaisian sandstone-rich redbed facies (Buchan Formation of Cameron 1993a) which are commonly barren.
  
 
== 2. North Sea Carboniferous biozones ==
 
== 2. North Sea Carboniferous biozones ==
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The correlation of lithostratigraphical units between well sections is the fundamental palynostratigraphic methodology in hydrocarbon exploration. Claims that palynology provides only low-resolution biostratigraphy in the offshore Carboniferous (e.g. to stage level; Leeder et al. 1990b) are now seen as untenable (see [[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]). Correlation of miospore biozones now equals or exceeds the level of resolution achieved by most other Carboniferous fossil groups, with the notable exception of the ammonoids. Further, the framework provided by the biozones allows more detailed intra-biozonal correlations to be made. These may be based upon relatively short-lived palaeoclimatic or facies signals within the palynological data, or upon data from other disciplines such as geochemistry or wireline log analysis (Leeder et al. 1990b, Besly et al. 1993, Davies & McLean 1996, Pearce et al. 2005). Detailed analysis of closely sampled sections may allow the recognition of palynologically distinctive mud-stone or coal units. Correlation of these has provided the basis for detailed subdivision and correlation of Westphalian reservoir units (e.g. coal seam correlations in the Langsettian and Duckmantian of the Murdoch, Caister and Chiswick fields; and correlation of intra-reservoir units within the Murdoch–Caister reservoir sandstone unit). Case studies have been presented for the Murdoch field in McLean & Murray (1996) and McLean and Davies (1999), and for the Caister field in Ritchie & Pratsides (1993).
 
The correlation of lithostratigraphical units between well sections is the fundamental palynostratigraphic methodology in hydrocarbon exploration. Claims that palynology provides only low-resolution biostratigraphy in the offshore Carboniferous (e.g. to stage level; Leeder et al. 1990b) are now seen as untenable (see [[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]). Correlation of miospore biozones now equals or exceeds the level of resolution achieved by most other Carboniferous fossil groups, with the notable exception of the ammonoids. Further, the framework provided by the biozones allows more detailed intra-biozonal correlations to be made. These may be based upon relatively short-lived palaeoclimatic or facies signals within the palynological data, or upon data from other disciplines such as geochemistry or wireline log analysis (Leeder et al. 1990b, Besly et al. 1993, Davies & McLean 1996, Pearce et al. 2005). Detailed analysis of closely sampled sections may allow the recognition of palynologically distinctive mud-stone or coal units. Correlation of these has provided the basis for detailed subdivision and correlation of Westphalian reservoir units (e.g. coal seam correlations in the Langsettian and Duckmantian of the Murdoch, Caister and Chiswick fields; and correlation of intra-reservoir units within the Murdoch–Caister reservoir sandstone unit). Case studies have been presented for the Murdoch field in McLean & Murray (1996) and McLean and Davies (1999), and for the Caister field in Ritchie & Pratsides (1993).
  
The development of a higher-resolution miospore biozonation has also allowed more detailed lithostratigraphical interpretations. In particular, the recognition of biozone boundaries associated with some of the principal Westphalian marine bands provides a basis for refined correlations. Note that the Aegiranum, Maltby, Amaliae and Listeri marine bands are not associated with biozone boundaries in the scheme of Clayton et al. (1977), and the same is true for the Cambriense, Aegiranum, Maltby and Amaliae marine bands in the scheme of Maynard et al (1997; [[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]). In the current study, emphasis has been placed upon the relationship of palynostratigraphy to the distribution of marine bands, and biozone boundaries identified accordingly. This means that the present scheme has a relatively high-resolution correlation potential. Further, the stratal subdivisions that it provides are likely to be genetically related in a sequence stratigraphical or palaeoclimatological sense.
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The development of a higher-resolution miospore biozonation has also allowed more detailed lithostratigraphical interpretations. In particular, the recognition of biozone boundaries associated with some of the principal Westphalian marine bands provides a basis for refined correlations. Note that the Aegiranum, Maltby, Amaliae and Listeri marine bands are not associated with biozone boundaries in the scheme of Clayton et al. (1977), and the same is true for the Cambriense, Aegiranum, Maltby and Amaliae marine bands in the scheme of Maynard et al (1997; [[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]). In the current study, emphasis has been placed upon the relationship of palynostratigraphy to the distribution of marine bands, and biozone boundaries identified accordingly. This means that the present scheme has a relatively high-resolution correlation potential. Further, the stratal subdivisions that it provides are likely to be genetically related in a sequence strati-graphical or palaeoclimatological sense.
  
Application of the scheme in the area on the northern margin of the Southern North Sea Basin has allowed the recognition of a major intra-Westphalian unconformity. Here, sequences towards the centre of the basin preserve a more-or-less complete record of Langsettian, Duckmantian and early to mid-Bolsovian coal-bearing strata overlain by redbeds of late Bolsovian age. To the northeast, the strata immediately beneath the redbeds become older, although palynological evidence from the redbeds indicate that these remain of mid-Bolsovian age. Such age interpretations are difficult to reconcile with the lithostratigraphy of Cameron (1993b), but, in the lithostratigraphy of Besly (2002), the base of the Lower Ketch Formation unconformably overlies the Cleaver and Westoe formations (Figure 5). In well 44/21-3 (Pearce et al. 2005), the Lower Ketch Formation rests on early Bolsovian coal-bearing rocks of the Upper Cleaver Member (''sensu ''Besly 2002). Use of the new biozonation in wells slightly farther north indicates that strata above the horizon of the Aegiranum Marine Band are not preserved, and that the redbeds lie upon late Duckmantian strata. In wells still farther northeast the Ketch Formation shows progressive onlap of the early Duckmantian, Langsettian and Namurian. In such cases the base of the Ketch Formation is evident in the absence of several biozones across the unconformity (Pearce et al. 2005).
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Application of the scheme in the area on the northern margin of the Southern North Sea Basin has allowed the recognition of a major intra-Westphalian unconformity. Here, sequences towards the centre of the basin preserve a more-or-less complete record of Langsettian, Duckmantian and early to mid-Bolsovian coal-bearing strata overlain by redbeds of late Bolsovian age. To the northeast, the strata immediately beneath the redbeds become older, although palynological evidence from the red-beds indicate that these remain of mid-Bolsovian age. Such age interpretations are difficult to reconcile with the lithostratigraphy of Cameron (1993b), but, in the lithostratigraphy of Besly (2002), the base of the Lower Ketch Formation unconformably overlies the Cleaver and Westoe formations (Figure 5). In well 44/21-3 (Pearce et al. 2005), the Lower Ketch Formation rests on early Bolsovian coal-bearing rocks of the Upper Cleaver Member (''sensu ''Besly 2002). Use of the new biozonation in wells slightly farther north indicates that strata above the horizon of the Aegiranum Marine Band are not preserved, and that the red-beds lie upon late Duckmantian strata. In wells still farther northeast the Ketch Formation shows progressive onlap of the early Duckmantian, Langsettian and Namurian. In such cases the base of the Ketch Formation is evident in the absence of several biozones across the unconformity (Pearce et al. 2005).
  
 
The relationships of the Westphalian biozonation to the lithostratigraphic systems of Cameron (1993b) and Besly (2002) is shown in [[:File:YGS_CHR_02_CARB_FIG_06.jpg|Figure 6]]. Recognition of the biozones allows a level of calibration of the lithostratigraphic units. Importantly, the diachronous nature of the boundaries of the units defined by Cameron (1993b) become readily apparent where they cross biozone boundaries related to major marine bands, for example, where the biozones allow the discrimination of strata below the Aegiranum Marine Band (latest Duckmantian) from those of earliest Bolsovian age above that horizon.
 
The relationships of the Westphalian biozonation to the lithostratigraphic systems of Cameron (1993b) and Besly (2002) is shown in [[:File:YGS_CHR_02_CARB_FIG_06.jpg|Figure 6]]. Recognition of the biozones allows a level of calibration of the lithostratigraphic units. Importantly, the diachronous nature of the boundaries of the units defined by Cameron (1993b) become readily apparent where they cross biozone boundaries related to major marine bands, for example, where the biozones allow the discrimination of strata below the Aegiranum Marine Band (latest Duckmantian) from those of earliest Bolsovian age above that horizon.
  
Some of the boundaries of the lithostratigraphical units of Besly (2002) are defined by major marine bands that can be correlated with the palynostratigraphy ([[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]). Recognition of these marine bands, using palynological or other criteria, is key to accurate lithostratigraphic understanding of the Late Carboniferous of the North Sea.
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Some of the boundaries of the lithostratigraphical units of Besly (2002) are defined by major marine bands that can be correlated with the palynostratigraphy ([[:File:YGS_CHR_02_CARB_FIG_01.jpg|Figure 1]]). Recognition of these marine band, using palynological or other criteria, is key to accurate lithostratigraphic understanding of the Late Carboniferous of the North Sea.
  
 
=== 3.4 Low- to medium-resolution interwell correlation ===
 
=== 3.4 Low- to medium-resolution interwell correlation ===
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=== 3.5 Regional correlation ===
 
=== 3.5 Regional correlation ===
  
The miospore biozones are recognized over a large area of Carboniferous rocks from which few data have previously been available. The Carboniferous strata of the North Sea Basin link those of the UK and northwestern European Carboniferous basins. A better understanding of these basins will allow better correlation farther afield into eastern Europe (cf. Owens et al. 1978) and western North America. Central to this process is the recognition of significant laterally extensive marine horizons. Integration of palynofacies studies (e.g. Van de Laar & Fermont 1990) with spectral gamma-ray or geochemical data provides a means for the recognition and correlation of these marine bands in the subsurface (Davies & McLean 1996, McLean et al. 2002, Pearce et al. 2002).
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The miospore biozones are recognized over a large area of Carboniferous rocks from which few data have previously been available. The Carboniferous strata of the North Sea Basin link those of the UK and northwestern European Carboniferous basins. A better understanding of these basins will allow better correlation farther afield into eastern Europe (cf. Owens et al. 1978) and western North America. Central to this process is the recognition of significant laterally extensive marine horizons. Integration of palynofacies studies (e.g. Van de Laar & Fermont 1990) with spectral gamma-ray or geochemical data provides a means for the recognition and correlation of these marine bands in the subsurface (Davies & McLean 1996, McLean et al. 2002, Pearce et al. 2002).=== 3.6 Provenance studies ===
  
=== 3.6 Provenance studies ===
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Westphalian strata in the Southern North Sea Basin commonly contain reworked Devonian miospores and pre-Devonian acritarchs. The identification of re-working may provide constraints on the sedimentary provenance of the Westphalian rock material. Similar results are known from onshore Late Carboniferous strata (Streel & Bless 1980, McLean 1995b, Chisholm et al. 1996, McLean & Chisholm 1996). The palynological data provide information on the relatively recent sources of sediment compared to the ancient (often pre-Palaeozoic) sources identified by heavy-mineral studies (Morton et al. 2005). The recognition of re-worked older Carboniferous palynomorphs in Westphalian strata may provide information on the phases of intra-Carboniferous incision and erosion.=== 3.7 Offshore to onshore comparisons ===
  
Westphalian strata in the Southern North Sea Basin commonly contain reworked Devonian miospores and pre-Devonian acritarchs. The identification of re-working may provide constraints on the sedimentary provenance of the Westphalian rock material. Similar results are known from onshore Late Carboniferous strata (Streel & Bless 1980, McLean 1995b, Chisholm et al. 1996, McLean & Chisholm 1996). The palynological data provide information on the relatively recent sources of sediment compared to the ancient (often pre-Palaeozoic) sources identified by heavy-mineral studies (Morton et al. 2005). The recognition of re-worked older Carboniferous palynomorphs in Westphalian strata may provide information on the phases of intra-Carboniferous incision and erosion.
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This study is based upon a wealth of palynostratigraphical data from offshore Carboniferous sections. Synthesis of these indicates similarities and differences between the palynology of the offshore and the onshore basins and shows areas in which the biostratigraphic subdivisions of the onshore Carboniferous strata may be improved. A few examples are given here. Strati-graphically restricted late Viséan palynomorph assemblages from the Forth Approaches Basin contain miospore taxa described from the Carboniferous of the present-day Arctic (Ravn 1991). These have been only rarely described from coeval strata on shore in the Midland Valley of Scotland (Turner & McLean 1999), but have correlation potential and may provide information on vegetation migration pathways and palaeoclimate. Secondly, many distinctive but undescribed miospore taxa are known from the offshore Carboniferous. Similarly, forms described from the Carboniferous of the United States that are rare in the onshore UK, may be relatively common off shore. The stratigraphical potential of these for European palynostratigraphic correlation is gradually becoming appreciated.
 
 
=== 3.7 Offshore to onshore comparisons ===
 
 
 
This study is based upon a wealth of palynostratigraphical data from offshore Carboniferous sections. Synthesis of these indicates similarities and differences between the palynology of the offshore and the onshore basins and shows areas in which the biostratigraphic subdivisions of the onshore Carboniferous strata may be improved. A few examples are given here. Stratigraphically restricted late Viséan palynomorph assemblages from the Forth Approaches Basin contain miospore taxa described from the Carboniferous of the present-day Arctic (Ravn 1991). These have been only rarely described from coeval strata on shore in the Midland Valley of Scotland (Turner & McLean 1999), but have correlation potential and may provide information on vegetation migration pathways and palaeoclimate. Secondly, many distinctive but undescribed miospore taxa are known from the offshore Carboniferous. Similarly, forms described from the Carboniferous of the United States that are rare in the onshore UK, may be relatively common off shore. The stratigraphical potential of these for European palynostratigraphic correlation is gradually becoming appreciated.
 
  
 
== 4. Conclusions ==
 
== 4. Conclusions ==
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== References ==
 
== References ==
  
Besly, B. M. 2002. Late Carboniferous redbeds of the UK southern North Sea viewed in a regional context [abstract: pp. 17–19]. Paper presented at “Hydrocarbon resources of the Carboniferous, southern North Sea and surrounding onshore areas” conference, Yorkshire Geological Society, Sheffield, 2002. This volume: 225–226.  
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Besly, B. M. 2002. Late Carboniferous redbeds of the UK southern North Sea viewed in a regional context [abstract: pp. 17–19]. Paper presented at “Hydrocarbon resources of the Carboniferous, southern North Sea and surrounding onshore areas” conference, Yorkshire Geological Society, Sheffield, 2002. This volume: 225–226. Besly, B. M., S. D. Burley, P. Turner 1993. The late Carboniferous “Barren Red Bed” play of the Silver Pit area, southern North Sea. In ''Petroleum geology of northwest Europe: proceedings of the 4th conference'', J. R. Parker (ed.), 727–40. London: Geological Society. Bruce, D. R. S. & L. Stemmerik 2003. Carboniferous. In ''The millenium atlas: petroleum geology of the central and northern North Sea'', D. Evans, C. Graham, A. Armour, P. Bathurst (eds), 83–9. London: Geological Society.
 
 
Besly, B. M., S. D. Burley, P. Turner 1993. The late Carboniferous “Barren Red Bed” play of the Silver Pit area, southern North Sea. In ''Petroleum geology of northwest Europe: proceedings of the 4th conference'', J. R. Parker (ed.), 727–40. London: Geological Society.  
 
 
 
Bruce, D. R. S. & L. Stemmerik 2003. Carboniferous. In ''The millenium atlas: petroleum geology of the central and northern North Sea'', D. Evans, C. Graham, A. Armour, P. Bathurst (eds), 83–9. London: Geological Society.
 
  
 
Calver, M. A. 1968. Distribution of Westphalian marine faunas in northern England and adjoining areas. ''Yorkshire Geological Society, Proceedings ''37, 1–72.
 
Calver, M. A. 1968. Distribution of Westphalian marine faunas in northern England and adjoining areas. ''Yorkshire Geological Society, Proceedings ''37, 1–72.
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Higgs, K. T., G. Clayton, J. B. Keegan 1988. ''Stratigraphic and systematic palynology of the Tournaisian rocks of Ireland''. Special Paper 7, Geological Survey of Ireland, Dublin.
 
Higgs, K. T., G. Clayton, J. B. Keegan 1988. ''Stratigraphic and systematic palynology of the Tournaisian rocks of Ireland''. Special Paper 7, Geological Survey of Ireland, Dublin.
  
Leeder, M. R., S. R. Boldy, R. Raiswell, R. Cameron 1990a. The Carboniferous of the outer Moray Firth Basin, Quadrants 14 and 15, central North Sea. ''Marine and Petroleum Geology ''7, 29–37.  
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Leeder, M. R., S. R. Boldy, R. Raiswell, R. Cameron 1990a. The Carboniferous of the outer Moray Firth Basin, Quadrants 14 and 15, central North Sea. ''Marine and Petroleum Geology ''7, 29–37. Leeder, M. R., R. Raiswell, H. Al-Biatty, A. McMahon, M. Hardman 1990b. Carboniferous stratigraphy, sedimentation and correlation of well 48/3-3 in the Southern North Sea Basin: integrated use of palynology, natural gamma/sonic logs and carbon/sulphur geochemistry. ''Geological Society of London, Journal ''147, 287–300. Martin, C. A. L., P. A. Doubleday, S. A. Stewart 2002. Upper Carboniferous and Lower Permian tectonostratigraphy on the southern margin of the central North Sea. ''Geological Society of London, Journal ''159, 731–49.
 
 
Leeder, M. R., R. Raiswell, H. Al-Biatty, A. McMahon, M. Hardman 1990b. Carboniferous stratigraphy, sedimentation and correlation of well 48/3-3 in the Southern North Sea Basin: integrated use of palynology, natural gamma/sonic logs and carbon/sulphur geochemistry. ''Geological Society of London, Journal ''147, 287–300.  
 
 
 
Martin, C. A. L., P. A. Doubleday, S. A. Stewart 2002. Upper Carboniferous and Lower Permian tectonostratigraphy on the southern margin of the central North Sea. ''Geological Society of London, Journal ''159, 731–49.
 
  
 
Maynard, J. R. & R. E. Dunay 1999. Reservoirs of the Dinantian (Lower Carboniferous) play of the southern North Sea. In ''Petroleum geology of northwest Europe: proceedings of the 4th conference'', A. J. Fleet & S. A. R. Boldy (eds), 729–46. London: Geological Society.
 
Maynard, J. R. & R. E. Dunay 1999. Reservoirs of the Dinantian (Lower Carboniferous) play of the southern North Sea. In ''Petroleum geology of northwest Europe: proceedings of the 4th conference'', A. J. Fleet & S. A. R. Boldy (eds), 729–46. London: Geological Society.
  
Maynard, J. R, W. Hofmann, R. E. Dunay, P. N. Bentham, K. P. Dean, I. Watson 1997. The Carboniferous of western Europe: the development of a petroleum system. ''Petroleum Geoscience ''3, 97–115.  
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Maynard, J. R, W. Hofmann, R. E. Dunay, P. N. Bentham, K. P. Dean, I. Watson 1997. The Carboniferous of western Europe: the development of a petroleum system. ''Petroleum Geoscience ''3, 97–115. McLean, D. 1993. ''A palynostratigraphic classification of the Westphalian of the Southern North Sea Carboniferous Basin''. PhD thesis, University of Sheffield.
  
McLean, D. 1993. ''A palynostratigraphic classification of the Westphalian of the Southern North Sea Carboniferous Basin''. PhD thesis, University of Sheffield.
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Maynard, J. R, W. 1995a. A palynostratigraphic classification of the Westphalian of the Southern North Sea Carboniferous Basin [abstract]. Paper presented at “Stratigraphic advances in the offshore Devonian and Carboniferous rocks, UKCS and adjacent onshore areas” conference, Geological Society, London, 1995.
  
McLean, D. 1995a. A palynostratigraphic classification of the Westphalian of the Southern North Sea Carboniferous Basin [abstract]. Paper presented at “Stratigraphic advances in the offshore Devonian and Carboniferous rocks, UKCS and adjacent onshore areas” conference, Geological Society, London, 1995.
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Maynard, J. R, W. 1995b. Provenance of reworked palynomorphs from the Green-moor Rock (Langsettian, Late Carboniferous) near Sheffield, England. ''Review of Palaeobotany and Palynology ''89, 305–317. McLean, D. & J. I. Chisholm 1996. Reworked palynomorphs as provenance indicators in the Yeadonian of the Pennine Basin. ''Yorkshire Geological Society, Proceedings ''51, 141–51.
 
 
McLean, D. 1995b. Provenance of reworked palynomorphs from the Green-moor Rock (Langsettian, Late Carboniferous) near Sheffield, England. ''Review of Palaeobotany and Palynology ''89, 305–317.  
 
 
 
McLean, D. & J. I. Chisholm 1996. Reworked palynomorphs as provenance indicators in the Yeadonian of the Pennine Basin. ''Yorkshire Geological Society, Proceedings ''51, 141–51.
 
  
 
McLean, D. & S. J. Davies 1999. Constraints on the application of palynology to the correlation of Euramerican Late Carboniferous clastic hydrocarbon reservoirs. In ''Biostratigraphy in production and development geology'', R. W. Jones & M. D. Simmons (eds), 201– 218. Special Publication 152, Geological Society, London.
 
McLean, D. & S. J. Davies 1999. Constraints on the application of palynology to the correlation of Euramerican Late Carboniferous clastic hydrocarbon reservoirs. In ''Biostratigraphy in production and development geology'', R. W. Jones & M. D. Simmons (eds), 201– 218. Special Publication 152, Geological Society, London.
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Pearce, T. J., J. Martin, B. Besly, D. McLean 2002. Correlation of Coal Measures sequences from the Staffordshire coalfield based on the geochemical identification of marine bands – implications for the correlation of similar sequences in the southern North Sea [abstract: pp. 63–4]. Paper presented at “Hydrocarbon resources of the Carboniferous, southern North Sea and adjacent areas” conference'', ''Yorkshire Geological Society, Sheffield, 2002.
 
Pearce, T. J., J. Martin, B. Besly, D. McLean 2002. Correlation of Coal Measures sequences from the Staffordshire coalfield based on the geochemical identification of marine bands – implications for the correlation of similar sequences in the southern North Sea [abstract: pp. 63–4]. Paper presented at “Hydrocarbon resources of the Carboniferous, southern North Sea and adjacent areas” conference'', ''Yorkshire Geological Society, Sheffield, 2002.
  
Pearce, T. J., D. McLean, D. Wray, D. K. Wright, C. J. Jeans, E. W. Mearns 2005. Stratigraphy of the Upper Carboniferous Schooner Formation, southern North Sea: chemostratigraphy, mineralogy, palynology and Sm–Nd isotope analysis. This volume: 165–182.  
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Pearce, T. J., D. McLean, D. Wray, D. K. Wright, C. J. Jeans, E. W. Mearns 2005. Stratigraphy of the Upper Carboniferous Schooner Formation, southern North Sea: chemostratigraphy, mineralogy, palynology and Sm–Nd isotope analysis. This volume: 165–182. Ravn, R. L. 1991. ''Miospores from the Kekiktuk Formation (Lower Carboniferous), Endicott field area, Alaska North Slope''. Contribution 27, American Association of Stratigraphic Palynologists,
 
 
Ravn, R. L. 1991. ''Miospores from the Kekiktuk Formation (Lower Carboniferous), Endicott field area, Alaska North Slope''. Contribution 27, American Association of Stratigraphic Palynologists,
 
  
 
Riley, N. J. 1993. Dinantian (Lower Carboniferous) biostratigraphy and chronostratigraphy in the British Isles. ''Geological Society of London, Journal ''150, 427–46.
 
Riley, N. J. 1993. Dinantian (Lower Carboniferous) biostratigraphy and chronostratigraphy in the British Isles. ''Geological Society of London, Journal ''150, 427–46.
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Van de Laar, J. G. M. & W. J. J. Fermont 1990. The impact of marine transgressions on palynofacies: the Carboniferous Aegir Marine Band in borehole Kemperkoul-1. ''Mededelingen Rijks Geologische Dienst ''45, 75–89.
 
Van de Laar, J. G. M. & W. J. J. Fermont 1990. The impact of marine transgressions on palynofacies: the Carboniferous Aegir Marine Band in borehole Kemperkoul-1. ''Mededelingen Rijks Geologische Dienst ''45, 75–89.
  
Van de Laar, J. G. M. & C. J. Van der Zwan 1996. Palynostratigraphy and palynofacies reconstruction of the Upper Carboniferous of borehole “De Lutte–6” (East Twente, The Netherlands). ''Mededelingen Rijks Geologische Dienst ''55, 61–82.
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Van de Laar, J. G. M. & C. J. Van der Zwan 1996. Palynostratigraphy and palynofacies reconstruction of the Upper Carboniferous of borehole “De Lutte–6” (East Twente, The Netherlands). ''Mededelingen Rijks Geologische Dienst ''55, 61–82
  
 
== {{anchor|UnoMark27651222513984}} Appendix: Alphabetical list of cited palynomorph names ==
 
== {{anchor|UnoMark27651222513984}} Appendix: Alphabetical list of cited palynomorph names ==

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