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

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==== Geometry ====
 
==== Geometry ====
  
High-sinuosity channel deposits have been mapped in detail on shore in the UK by us at and around Waverly East opencast site, and previously by BP (Eagle Sandstone reservoir) in the Beckingham oilfield. These studies indicate a maximum thickness of 20–25 m and lateral continuity for up to 1 km perpendicular to palaeoflow and for several kilometres or tens of kilometres parallel to palaeoflow. Although produced by high-sinuosity channel activity, the deposits preserved consist of many point bar units and commonly form relatively straight channel belts.
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High-sinuosity channel deposits have been mapped in detail on shore in the UK by us at and around Waverly East opencast site, and previously by BP (Eagle Sandstone reservoir) in the Beckingham oilfield. These studies indicate a maximum thickness of 20–25m and lateral continuity for up to 1km perpendicular to palaeoflow and for several kilometres or tens of kilometres parallel to palaeoflow. Although produced by high-sinuosity channel activity, the deposits preserved consist of many point bar units and commonly form relatively straight channel belts.
  
 
==== Wireline log characteristics ====
 
==== Wireline log characteristics ====
  
Facies Ch is invariably characterized by sharp basal gamma-ray and sonic-log inflexions. However, the upper contact may be either sharp or more gradational, depending upon the lithologies developed. The gamma log response is typically in the range 60–75&nbsp;API reflecting the argillaceous nature of the sandstones. It is typically accompanied by a sonic log response of 80–90&nbsp;µsft<sup>–1</sup>. The main variations in wireline log profiles occur in the upper part of sandstone units where gamma log response and δ''T ''values may increase markedly because of the presence of finer-grained units. δ''T ''values tend to decrease sharply at well cemented or concretionary beds.
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Facies Ch is invariably characterized by sharp basal gamma-ray and sonic-log inflexions. However, the upper contact may be either sharp or more gradational, depending upon the lithologies developed. The gamma log response is typically in the range 60– 75API reflecting the argillaceous nature of the sandstones. It is typically accompanied by a sonic log response of 80–90µsft<sup>–1</sup>. The main variations in wireline log profiles occur in the upper part of sandstone units where gamma log response and δ''T ''values may increase markedly because of the presence of finer-grained units. δ''T ''values tend to decrease sharply at well cemented or concretionary beds.
  
 
=== Facies Cd – Distributary mouth bar ===
 
=== Facies Cd – Distributary mouth bar ===
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==== Description ====
 
==== Description ====
  
Distributary mouth-bar deposits coarsen upwards overall and comprise an upper sandstone unit overlying a lower mudstone– siltstone unit. The lower mudstone–siltstone unit is typically 10– 15&nbsp;m thick and may contain either a marine or non-marine fauna. Overlying sandstones are well sorted and fairly clean, and they generally increase in grain size upwards from very fine to fine; however, they may locally be coarse and may fine upwards. Mudstones and siltstones are mostly parallel laminated or locally homogenized by bioturbation, particularly at marine horizons. The sandstones tend to be ripple cross laminated near the base and trough cross bedded at higher levels. Distributary mouth-bar units are commonly underlain and overlain by coal seams or rooty horizons.
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Distributary mouth-bar deposits coarsen upwards overall and comprise an upper sandstone unit overlying a lower mudstone– siltstone unit. The lower mudstone–siltstone unit is typically 10– 15m thick and may contain either a marine or non-marine fauna. Overlying sandstones are well sorted and fairly clean, and they generally increase in grain size upwards from very fine to fine; however, they may locally be coarse and may fine upwards. Mudstones and siltstones are mostly parallel laminated or locally homogenized by bioturbation, particularly at marine horizons. The sandstones tend to be ripple cross laminated near the base and trough cross bedded at higher levels. Distributary mouth-bar units are commonly underlain and overlain by coal seams or rooty horizons.
  
 
==== Interpretation ====
 
==== Interpretation ====

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