Editing Fluvial sandbody architecture, cyclicity and sequence stratigraphic setting – implications for hydrocarbon reservoirs: the Westphalian C and D of the Osnabrück–Ibbenbüren area, northwest Germany

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|-  
 
|-  
 
|| 2
 
|| 2
|| Typically 120–200 m
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|| Typically 120–20 0m
 
|| Upwards-fining cycles, characterized by thick, stacked, coarse-grained channels at base and multiple coal-palaeosol horizons at the top. Typically contain 2–3 smaller-scale upwards-fining third-order cycles; each successive third-order cycle containing less sand.
 
|| Upwards-fining cycles, characterized by thick, stacked, coarse-grained channels at base and multiple coal-palaeosol horizons at the top. Typically contain 2–3 smaller-scale upwards-fining third-order cycles; each successive third-order cycle containing less sand.
 
|| Hinterland tectonic pulses, e.g. movement along the Tornquist–Teisseyre or Rynkøbing Fyn High Zone. Produces large pulses of sediment flux.
 
|| Hinterland tectonic pulses, e.g. movement along the Tornquist–Teisseyre or Rynkøbing Fyn High Zone. Produces large pulses of sediment flux.
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==== 3.2.1 Evidence for Variscan tectonic influence ====
 
==== 3.2.1 Evidence for Variscan tectonic influence ====
  
Towards the end of the Carboniferous ([[:File:YGS_CHR_05_FLUV_FIG_08.jpg|Figure 8]]), the Gondwanan plate collided with both the Laurentian plate to the west and the Iberian plate to the south, linked as part of the Asturian deformation phase of the Variscan orogeny (Warr 2000). The principal direction of Variscan convergence was probably towards the north and northwest as part of an oblique (dextral) collisional regime. By about Bolsovian–Westphalian D times the final Asturian phase of deformation began, which ultimately led to the formation of the Pangaean supercontinent ([[:File:YGS_CHR_05_FLUV_FIG_08.jpg|Figure 8]]). This closed off the Rheic Ocean such that all access to the sea was cut off in central Europe and the UK (Maynard et al. 1997). There is clear evidence that Variscan orogenic processes affected northern Germany during the Westphalian and Stephanian, and that the deformation front migrated northwards. This gave rise to a flexural foreland basin and the northwards migration of the depocentre, with the result that alluvial-plain sedimentation became dominant in Germany, with sediment being supplied from the uplifted Variscan mountain belt to the south and east. The evidence for this includes:
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Towards the end of the Carboniferous ([[:File:YGS_CHR_05_FLUV_FIG_08.jpg|Figure 8]]), the Gondwanan plate collided with both the Laurentian plate to the west and the Iberian plate to the south, linked as part of the Asturian deformation phase of the Variscan orogeny (Warr 2000). The principal direction of Variscan convergence was probably towards the north and northwest as part of an oblique (dextral) collisional regime. By about Bolsovian–Westphalian D times the final Asturian phase of deformation began, which ultimately led to the formation of the Pangaean supercontinent ([[:File:YGS_CHR_05_FLUV_FIG_08.jpg|Figure 8]]). This closed
* Isopachs with a strongly asymmetrical pattern ([[:File:YGS_CHR_05_FLUV_FIG_09.jpg|Figure 9]]), with up to 4 km of strata accumulating in northern Germany (Drozdzewski 1993). This can be explained by flexure of the crust in advance of loading by Variscan nappes.
+
 
 +
off the Rheic Ocean such that all access to the sea was cut off in central Europe and the UK (Maynard et al. 1997). There is clear evidence that Variscan orogenic processes affected northern Germany during the Westphalian and Stephanian, and that the deformation front migrated northwards. This gave rise to a flexural foreland basin and the northwards migration of the depocentre, with the result that alluvial-plain sedimentation became dominant in Germany, with sediment being supplied from the uplifted Variscan mountain belt to the south and east. The evidence for this includes:* Isopachs with a strongly asymmetrical pattern ([[:File:YGS_CHR_05_FLUV_FIG_09.jpg|Figure 9]]), with up to 4km of strata accumulating in northern Germany (Drozdzewski 1993). This can be explained by flexure of the crust in advance of loading by Variscan nappes.
 
* The recognition of a disconformity between Westphalian and Stephanian strata in northern Germany (Hedemann & Teichmüller 1971, Hedemann et al. 1984), linked to Variscan uplift.
 
* The recognition of a disconformity between Westphalian and Stephanian strata in northern Germany (Hedemann & Teichmüller 1971, Hedemann et al. 1984), linked to Variscan uplift.
 
* During Bolsovian and younger times, Variscan uplift led to a significant increase in the amount of sediment delivered into the basin, with some associated re-working of pre-existing basin material (Gayer et al. 1993, Jankowski et al. 1993). This high proportion of sandstones is particularly marked in the east, in the Hamwiede Schneverdingen and South Oldenburg areas, and there is a progressive decrease westwards and northwestwards towards the Ems area ([[:File:YGS_CHR_05_FLUV_FIG_03.jpg|Figure 3]], [[:File:YGS_CHR_05_FLUV_FIG_07.jpg|Figure 7]]). Palaeocurrent data for these channel sandbodies show strongly unidirectional flow directions towards the west and northwest, away from the rising Variscan mountains ([[:File:YGS_CHR_05_FLUV_FIG_06.jpg|Figure 6]]).
 
* During Bolsovian and younger times, Variscan uplift led to a significant increase in the amount of sediment delivered into the basin, with some associated re-working of pre-existing basin material (Gayer et al. 1993, Jankowski et al. 1993). This high proportion of sandstones is particularly marked in the east, in the Hamwiede Schneverdingen and South Oldenburg areas, and there is a progressive decrease westwards and northwestwards towards the Ems area ([[:File:YGS_CHR_05_FLUV_FIG_03.jpg|Figure 3]], [[:File:YGS_CHR_05_FLUV_FIG_07.jpg|Figure 7]]). Palaeocurrent data for these channel sandbodies show strongly unidirectional flow directions towards the west and northwest, away from the rising Variscan mountains ([[:File:YGS_CHR_05_FLUV_FIG_06.jpg|Figure 6]]).
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Although it is clear that a sea-level linkage could produce the cyclicity described, there is no direct evidence for such a control. Elsewhere in Europe and North America there is good support for Upper Carboniferous base-level changes being driven by glacio-eustatic sea-level rises (Holdsworth & Collinson 1988, Maynard & Leeder 1992, Flint et al. 1995). However, most of this evidence comes from Namurian and early Westphalian strata, and, as discussed previously, the structural setting of northern Germany in the Bolsovian suggests that the Rheic Ocean had closed and that there was no direct marine connection to this basin (Maynard et al. 1997). In an inland basin such as this it is often difficult to be sure of the role that sea level has on facies patterns. If sea level was controlling the local base level, then this must represent a subtle influence that is not represented in the preserved succession by marine facies. No marine or tidal facies were identified from upper Westphalian and Stephanian successions in this area.
 
Although it is clear that a sea-level linkage could produce the cyclicity described, there is no direct evidence for such a control. Elsewhere in Europe and North America there is good support for Upper Carboniferous base-level changes being driven by glacio-eustatic sea-level rises (Holdsworth & Collinson 1988, Maynard & Leeder 1992, Flint et al. 1995). However, most of this evidence comes from Namurian and early Westphalian strata, and, as discussed previously, the structural setting of northern Germany in the Bolsovian suggests that the Rheic Ocean had closed and that there was no direct marine connection to this basin (Maynard et al. 1997). In an inland basin such as this it is often difficult to be sure of the role that sea level has on facies patterns. If sea level was controlling the local base level, then this must represent a subtle influence that is not represented in the preserved succession by marine facies. No marine or tidal facies were identified from upper Westphalian and Stephanian successions in this area.
  
Alternatively, third-order cycles could be driven purely by tectonic processes, possibly linked to short-term episodes of crustal loading (see Miall 1996: 477). However, such a mechanism alone may not produce the high-frequency events required to drive the cyclicity at this scale. Although not well constrained, it is thought likely that these third-order cycles have a timespan comparable with fourth-order sea-level cycles (10<sup>5</sup> years).
+
Alternatively, third-order cycles could be driven purely by tectonic processes, possibly linked to short-term episodes of crustal loading (see Miall 1996: 477). However, such a mechanism alone may not produce the high-frequency events required to drive the cyclicity at this scale. Although not well constrained, it is thought likely that these third-order cycles have a timespan comparable with fourth-order sea-level cycles (105 years).
  
 
Hoffman & Grotzinger (1993) suggest that the climatic belt in which an orogen develops influences the tectonic style of the orogen and the architecture of the adjacent foreland basin. Monsoonal belts, such as those that would have characterized Upper Carboniferous times, would be typified by high rates of precipitation, leading to rapid erosional unroofing, deep erosion and the rapid filling of the foreland basin with sediment (Sinclair & Allen 1992, Hoffman & Grotzinger 1993). Drier periods would have less vegetation cover and hence would be characterized by increased erosion of bedrock, which would result in large volumes of material being available for transportation (Schumm 1968, Cecil 1990).
 
Hoffman & Grotzinger (1993) suggest that the climatic belt in which an orogen develops influences the tectonic style of the orogen and the architecture of the adjacent foreland basin. Monsoonal belts, such as those that would have characterized Upper Carboniferous times, would be typified by high rates of precipitation, leading to rapid erosional unroofing, deep erosion and the rapid filling of the foreland basin with sediment (Sinclair & Allen 1992, Hoffman & Grotzinger 1993). Drier periods would have less vegetation cover and hence would be characterized by increased erosion of bedrock, which would result in large volumes of material being available for transportation (Schumm 1968, Cecil 1990).
  
Olsen (1990) recognized two scales of cyclicity from Devonian meandering channel systems from east Greenland, one of the order of ''c''. 20&nbsp;m thick and a higher-order one at ''c. ''100&nbsp;m. He attributed these to climatic variations as a result of changes in Earth’s orbital parameters, reflecting 20000&nbsp;yr Milankovitch precession cycles with modulation by ''c. ''110000&nbsp;yr eccentricity cycles. Although it is possible that Milankovitch orbital forcing could account for the third-order cycles described here, the structural setting in northern Germany at this time makes it more likely that these cycles represent the product of changes in the balance between tectonically induced accommodation and climatically modulated sediment supply. Similar climatic controls on Carboniferous and Devonian non-marine successions have been described respectively by Glover & Powell (1996) and McKie & Garden (1996).
+
Olsen (1990) recognized two scales of cyclicity from Devonian meandering channel systems from east Greenland, one of the order of ''c''. 20m thick and a higher-order one at ''c. ''100m. He attributed these to climatic variations as a result of changes in Earth’s orbital parameters, reflecting 20000yr Milankovitch precession cycles with modulation by ''c. ''110000yr eccentricity cycles. Although it is possible that Milankovitch orbital forcing could account for the third-order cycles described here, the structural setting in northern Germany at this time makes it more likely that these cycles represent the product of changes in the balance between tectonically induced accommodation and climatically modulated sediment supply. Similar climatic controls on Carboniferous and Devonian non-marine successions have been described respectively by Glover & Powell (1996) and McKie & Garden (1996).
  
It is proposed that times of hinterland uplift resulted in greater orographic precipitation and hence the basal channel-belt-dominated parts of each third-order cycle reflect the rapid expansion of fluvial systems as the amount of clastic flux outstrips the accommodation space available. The change in fluvial style upwards through a cycle and the increased frequency of coals and other floodplain deposits indicates a decrease in the efficiency of the fluvial systems, a reduction in stream gradients and an elevation of the groundwater table. In a hydrographically enclosed system such as this, high rates of precipitation and any concomitant basinal subsidence would increase both the amount of sediment aggradation and raise the base level. Thus, relative base-level (effective lake-level) rise results in the progressive drowning of fluvial systems. The resulting decrease in the efficiency of the fluvial systems to transport the coarse clastic fraction is thought to be the main cause of the change from low- to relatively high-sinuosity fluvial systems and ultimately into floodplain conditions.
+
It is proposed that times of hinterland uplift resulted in greater orographic precipitation and hence the basal channel-belt-dominated parts of each third-order cycle reflect the rapid expansion of fluvial systems as the amount of clastic flux outstrips the accommodation space available. The change in fluvial style upwards through a cycle and the increased frequency of coals and other floodplain deposits indicates a decrease in the efficiency of the fluvial systems, a reduction in stream gradients and an elevation of the groundwater table. In a hydrographically enclosed system such as this, high rates of precipitation and any concomitant basinal subsidence would increase both the amount of sediment aggradation and raise the base level. Thus, relative base-level (effective lake-level) rise results in the progressive drowning of fluvial systems. The resulting decrease in the efficiency of the fluvial systems to transport the coarse clastic fraction is thought to be the main cause of the change from low-to relatively high-sinuosity fluvial systems and ultimately into floodplain conditions.
  
 
This hypothesis is difficult to prove conclusively, as evidence for intra-cycle variations in climate is lacking in these successions. However, climatically controlled facies changes have been proven from the Westphalian D and younger successions of northern Germany and the UK, and primary redbed facies, including calcretes and localized alluvial fans, all indicate deposition under increasingly drier and more arid conditions, linked to the growth of a rain shadow associated with uplift of the Variscan mountains (Besly 1987, 1988). It is also known that in younger Westphalian D and Stephanian successions, the effects of increased evapotranspiration are manifested by a change to better-drained palaeosols and an absence of coals upwards through a cycle. This may indirectly support the view that climatic controls operated during earlier times.
 
This hypothesis is difficult to prove conclusively, as evidence for intra-cycle variations in climate is lacking in these successions. However, climatically controlled facies changes have been proven from the Westphalian D and younger successions of northern Germany and the UK, and primary redbed facies, including calcretes and localized alluvial fans, all indicate deposition under increasingly drier and more arid conditions, linked to the growth of a rain shadow associated with uplift of the Variscan mountains (Besly 1987, 1988). It is also known that in younger Westphalian D and Stephanian successions, the effects of increased evapotranspiration are manifested by a change to better-drained palaeosols and an absence of coals upwards through a cycle. This may indirectly support the view that climatic controls operated during earlier times.
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=== 4.1 Exploration scale ===
 
=== 4.1 Exploration scale ===
  
Reservoir distribution is related to basin-scale processes that have interacted to produce cyclical sequences such that potential reservoirs are not randomly distributed through the stratigraphical succession, as would be predicted by a purely stochastic model. Correlations shows that thick stacked sandbodies with high net-to-gross ratios not only occur in the more proximal (southeastern) parts of the basin but can also be predicted to occur in the medial parts, where they will be preferentially stacked at the bases of first-order cycles on a repetitive vertical scale of approximately 160–200&nbsp;m ([[:File:YGS_CHR_05_FLUV_FIG_10.jpg|Figure 10]]). On a regional scale, second- and third-order cycles are more difficult to correlate, indicating some lateral variability.
+
Reservoir distribution is related to basin-scale processes that have interacted to produce cyclical sequences such that potential reservoirs are not randomly distributed through the stratigraphical succession, as would be predicted by a purely stochastic model. Correlations shows that thick stacked sandbodies with high net-to-gross ratios not only occur in the more proximal (southeastern) parts of the basin but can also be predicted to occur in the medial parts, where they will be preferentially stacked at the bases of first-order cycles on a repetitive vertical scale of approximately 160–200m ([[:File:YGS_CHR_05_FLUV_FIG_10.jpg|Figure 10]]). On a regional scale, second- and third-order cycles are more difficult to correlate, indicating some lateral variability.
  
This work has identified stratigraphical levels within the Bolsovian, which are more sand prone, providing a predictive framework for exploration. Typically, a cycle is 160–200&nbsp;m thick and commences with a widely developed sandstone complex, covering areas of tens to hundreds of square kilometres ([[:File:YGS_CHR_05_FLUV_FIG_10.jpg|Figure 10]]). Such sandstone-prone intervals locally form important gas reservoirs in northwest Germany and also in northeast Netherlands (e.g. the “Tubbergen Sandstone”). Although probably part of a different depositional system, similar sequences and regionally developed sandstone complexes have been identified in the Dutch–UK offshore (S. Kelly, personal communication, 2003).
+
This work has identified stratigraphical levels within the Bolsovian, which are more sand prone, providing a predictive framework for exploration. Typically, a cycle is 160–200m thick and commences with a widely developed sandstone complex, covering areas of tens to hundreds of square kilometres ([[:File:YGS_CHR_05_FLUV_FIG_10.jpg|Figure 10]]). Such sandstone-prone intervals locally form important gas reservoirs in northwest Germany and also in northeast Netherlands (e.g. the “Tubbergen Sandstone”). Although probably part of a different depositional system, similar sequences and regionally developed sandstone complexes have been identified in the Dutch–UK offshore (S. Kelly, personal communication, 2003).
  
 
=== 4.2 Field scale ===
 
=== 4.2 Field scale ===
  
The distribution of reservoir and reservoir-quality variations within a Carboniferous field is typically a complex problem, with reservoir volume, connectivity and productivity being particular issues. In the early phase of field life, there is little hard data; reservoirs are modelled either stochastically or objectively with a stochastic component to try to “capture” uncertainty. Volumetrics, well planning and production profiles rely on the accuracy of actual data and analogue input to these models. A robust correlation framework and an understanding of sandbody types and distribution are needed.
+
The distribution of reservoir and reservoir-quality variations within a Carboniferous field is typically a complex problem, with reservoir volume, connectivity and productivity being particular issues. In the early phase of field life, there is little hard data; reservoirs are modelled either stochastically or objectively with a stochastic component to try to “capture” uncertainty.
 +
 
 +
Volumetrics, well planning and production profiles rely on the accuracy of actual data and analogue input to these models. A robust correlation framework and an understanding of sandbody types and distribution are needed.
  
 
The work presented here predicts that high net-to-gross reservoirs should be field wide or greater in extent and possess a distinct layering, alternating with floodplain fines. These sandstone bodies are concentrated towards the bases of second-order cycles, with narrower, more ribbon-like, heterolithic sands located higher in the cycles. The reservoirs are clearly layered on a second-order scale, with the tops of cycles comprising mud-dominated floodplain and lacustrine associations that are laterally continuous on a field scale and hence form potential barriers to fluid flow (see [[:File:YGS_CHR_05_FLUV_FIG_03.jpg|Figure 3]]b). The recognition of second- and third-order cyclicity allows correlation of channel-belt scale sandbodies rather than individual channels.
 
The work presented here predicts that high net-to-gross reservoirs should be field wide or greater in extent and possess a distinct layering, alternating with floodplain fines. These sandstone bodies are concentrated towards the bases of second-order cycles, with narrower, more ribbon-like, heterolithic sands located higher in the cycles. The reservoirs are clearly layered on a second-order scale, with the tops of cycles comprising mud-dominated floodplain and lacustrine associations that are laterally continuous on a field scale and hence form potential barriers to fluid flow (see [[:File:YGS_CHR_05_FLUV_FIG_03.jpg|Figure 3]]b). The recognition of second- and third-order cyclicity allows correlation of channel-belt scale sandbodies rather than individual channels.
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The observed stacking patterns and cyclicity would fit into a sequence stratigraphical model, whereby base-level changes, controlled by glacio-eustatic sea-level oscillations, and there is good evidence for such processes occurring in the Upper Carboniferous. However, tectonic processes operating in both the basin and adjacent orogenic zones are thought more likely to have exerted the dominant control. Variscan compressional activities which took place farther to the south during the Bolsovian–Westphalian D, not only affected the amount and type of sediment delivered into the basin but also controlled the generation of accommodation space in the basin. This is good evidence that tectonic processes controlled the generation of cycles and stacking patterns within each cycle. It is also suggested that there is a distinct climatic signature controlling cyclicity, modulating the stacking patterns and ultimately impacting on fluvial style.
 
The observed stacking patterns and cyclicity would fit into a sequence stratigraphical model, whereby base-level changes, controlled by glacio-eustatic sea-level oscillations, and there is good evidence for such processes occurring in the Upper Carboniferous. However, tectonic processes operating in both the basin and adjacent orogenic zones are thought more likely to have exerted the dominant control. Variscan compressional activities which took place farther to the south during the Bolsovian–Westphalian D, not only affected the amount and type of sediment delivered into the basin but also controlled the generation of accommodation space in the basin. This is good evidence that tectonic processes controlled the generation of cycles and stacking patterns within each cycle. It is also suggested that there is a distinct climatic signature controlling cyclicity, modulating the stacking patterns and ultimately impacting on fluvial style.
  
A better understanding of fluvial style, architecture and stacking patterns leads to benefits in the understanding of hydrocarbon reservoirs. The deterministic nature of the facies is an important feature to bear in mind when modelling reservoirs. It is evident that these high net-to-gross Upper Carboniferous reservoirs are clearly layered and vertically compartmentalized. Thus, the implications for modelling is that such systems cannot be modelled simplistically as a “tank of sand” and detailed assessment and correlation is required in order to identify and distinguish intra-reservoir baffles, such as remnant overbanks and barform drapes.
+
A better understanding of fluvial style, architecture and stacking patterns leads to benefits in the understanding of hydrocarbon reservoirs. The deterministic nature of the facies is an important feature to bear in mind when modelling reservoirs. It is evident that these high net-to-gross Upper Carboniferous reservoirs are clearly layered and vertically compartmentalized.
 +
 
 +
Thus, the implications for modelling is that such systems cannot be modelled simplistically as a “tank of sand” and detailed assessment and correlation is required in order to identify and distinguish intra-reservoir baffles, such as remnant overbanks and barform drapes.
  
 
== Acknowledgements ==
 
== Acknowledgements ==
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Besly, B. M. 1987. Sedimentological evidence for Carboniferous and Early Permian palaeoclimates of Europe. ''Extrait des Annales de la Société Géologique du Nord ''151, 131–43.
 
Besly, B. M. 1987. Sedimentological evidence for Carboniferous and Early Permian palaeoclimates of Europe. ''Extrait des Annales de la Société Géologique du Nord ''151, 131–43.
  
Besly, B. M. 1988. Palaeogeographic implications of late Westphalian to early Permian redbeds, Central England. In ''Sedimentation in a synorogenic basin complex: the Upper Carboniferous of northwest Europe'', B. M. Besly & G. Kelling (eds), 200–221. Glasgow: Blackie.  
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Besly, B. M. 1988. Palaeogeographic implications of late Westphalian to early Permian redbeds, Central England. In ''Sedimentation in a synorogenic basin complex: the Upper Carboniferous of northwest Europe'', B. M. Besly & G. Kelling (eds), 200–221. Glasgow: Blackie. Bridge, J. S. 1985. Paleochannel patterns inferred from alluvial deposits: a critical evaluation. ''Journal of Sedimentary Petrology ''55, 579–89.
 
 
Bridge, J. S. 1985. Paleochannel patterns inferred from alluvial deposits: a critical evaluation. ''Journal of Sedimentary Petrology ''55, 579–89.
 
  
 
Bristow, C. S. 1987. Brahmaputra River: channel migration and deposition. In ''Recent developments in fluvial sedimentology'', F. G. Ethridge, R. M. Flores, M. D. Harvey (eds), 63–74. Special Publication 39, Society of Economic Paleontologists and Mineralogists, Tulsa, Oklahoma.
 
Bristow, C. S. 1987. Brahmaputra River: channel migration and deposition. In ''Recent developments in fluvial sedimentology'', F. G. Ethridge, R. M. Flores, M. D. Harvey (eds), 63–74. Special Publication 39, Society of Economic Paleontologists and Mineralogists, Tulsa, Oklahoma.
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Glover, B. W. & J. H. Powell 1996. Interaction of climate and tectonics upon alluvial architecture: Late Carboniferous–Early Permian sequences at the southern margin of the Pennine Basin. ''Palaeogeography, Palaeoclimatology, Palaeoecology ''121, 13–34.
 
Glover, B. W. & J. H. Powell 1996. Interaction of climate and tectonics upon alluvial architecture: Late Carboniferous–Early Permian sequences at the southern margin of the Pennine Basin. ''Palaeogeography, Palaeoclimatology, Palaeoecology ''121, 13–34.
  
Glover, B. W. & N. S. Jones 1997. Systematic distribution of coals within the Westphalian C–D succession of NW Germany and their implications for sequence stratigraphy. Coal Geology Workshop “Sequence Stratigraphy Applied to Coal-Bearing Strata: Quo Vadis?”, organized by VITO, March 1997, Hasselt, Belgium.  
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Glover, B. W. & N. S. Jones 1997. Systematic distribution of coals within the Westphalian C–D succession of NW Germany and their implications for sequence stratigraphy. Coal Geology Workshop “Sequence Stratigraphy Applied to Coal-Bearing Strata: Quo Vadis?”, organized by VITO, March 1997, Hasselt, Belgium. Hallsworth, C. R. & J. I. Chisholm 2000. Stratigraphic evolution of provenance characteristics in Westphalian sandstones of the
  
Hallsworth, C. R. & J. I. Chisholm 2000. Stratigraphic evolution of provenance characteristics in Westphalian sandstones of the Yorkshire coalfield. ''Yorkshire Geological Society, Proceedings ''53, 43–72.
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Yorkshire coalfield. ''Yorkshire Geological Society, Proceedings ''53, 43–72.
  
 
Hallsworth, C. R., A. C. Morton, J. Claoué-Long, C. M. Fanning 2000. Carboniferous sand provenance in the Pennine Basin, UK: constraints from heavy-mineral and detrital-zircon age data. ''Sedimentary Geology ''137, 147–85.
 
Hallsworth, C. R., A. C. Morton, J. Claoué-Long, C. M. Fanning 2000. Carboniferous sand provenance in the Pennine Basin, UK: constraints from heavy-mineral and detrital-zircon age data. ''Sedimentary Geology ''137, 147–85.
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Hoyer, P., J. Leisser, M. Teichmüller, R. Teichmüller 1971. Chapter 3. The Carboniferous of Ibbenbüren, the Hüggel and the Piesberg, (c): metamorphism of coal. The Carboniferous Deposits in the Federal Republic of Germany. ''Fortschritte in der Geologie von Rheinland und Westfalen ''19, 87–90.
 
Hoyer, P., J. Leisser, M. Teichmüller, R. Teichmüller 1971. Chapter 3. The Carboniferous of Ibbenbüren, the Hüggel and the Piesberg, (c): metamorphism of coal. The Carboniferous Deposits in the Federal Republic of Germany. ''Fortschritte in der Geologie von Rheinland und Westfalen ''19, 87–90.
  
Jackson, R. G. 1976. Depositional model of point bars in the lower Wabash River. ''Journal of Sedimentary Petrology ''46, 579–94.  
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Jackson, R. G. 1976. Depositional model of point bars in the lower Wabash River. ''Journal of Sedimentary Petrology ''46, 579–94. Jankowski, B., F. David, V. Selter 1993. Facies complexes of the Upper Carboniferous in northwest Germany and their structural implications. In ''Rhenohercynian and Subvariscan fold belts'', R. A. Gayer, R. O. Greilling, A. K. Vogel (eds), 139–58. Wiesbaden: Vieweg.
 
 
Jankowski, B., F. David, V. Selter 1993. Facies complexes of the Upper Carboniferous in northwest Germany and their structural implications. In ''Rhenohercynian and Subvariscan fold belts'', R. A. Gayer, R. O. Greilling, A. K. Vogel (eds), 139–58. Wiesbaden: Vieweg.
 
  
 
Jervey, M. T. 1988. Quantitative geological modeling of siliciclastic rock sequences and their seismic expression. In ''Sea-level changes: an integrated approach'', C. K. Wilgus, B. S. Hastings, C. G. St C. Kendall, H. W. Posamentier, C. A. Ross, J. C. Van Wagoner (eds), 47–69. Special Publication 42, Society of Economic Paleontologists and Mineralogists, Tulsa, Oklahoma.
 
Jervey, M. T. 1988. Quantitative geological modeling of siliciclastic rock sequences and their seismic expression. In ''Sea-level changes: an integrated approach'', C. K. Wilgus, B. S. Hastings, C. G. St C. Kendall, H. W. Posamentier, C. A. Ross, J. C. Van Wagoner (eds), 47–69. Special Publication 42, Society of Economic Paleontologists and Mineralogists, Tulsa, Oklahoma.
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Miall, A. D. 1996. ''The geology of fluvial deposits: sedimentary facies, basin analysis, and petroleum geology''. Berlin: Springer.
 
Miall, A. D. 1996. ''The geology of fluvial deposits: sedimentary facies, basin analysis, and petroleum geology''. Berlin: Springer.
  
Miall, A. D. 1997. ''The geology of stratigraphic sequences''. Berlin: Springer.  
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Miall, A. D. 1997. ''The geology of stratigraphic sequences''. Berlin: Springer. Morton, A. C., J. C. Claoué-Long, C. R. Hallsworth 2001. Zircon-age and heavy-mineral constraints on provenance of North Sea Carboniferous sandstones. ''Marine and Petroleum Geology ''18, 319–37. Morton, A. C., C. Hallsworth, A. Mosciarello 2005. Interplay between northern and southern sediment sources during Westphalian deposition in the Silverpit Basin, southern North Sea. This volume: 135– 146.
 
 
Morton, A. C., J. C. Claoué-Long, C. R. Hallsworth 2001. Zircon-age and heavy-mineral constraints on provenance of North Sea Carboniferous sandstones. ''Marine and Petroleum Geology ''18, 319–37.  
 
 
 
Morton, A. C., C. Hallsworth, A. Mosciarello 2005. Interplay between northern and southern sediment sources during Westphalian deposition in the Silverpit Basin, southern North Sea. This volume: 135– 146.
 
  
 
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