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

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==== Wireline log characteristics ====
 
==== Wireline log characteristics ====
  
Facies Oc is characterized by very erratic gamma-ray and sonic-log responses, reflecting the variable interbedding of lithologies. Gamma-log response increases from 120–>150&nbsp;API in the underlying facies Ol mudstones–siltstones to 75–105&nbsp;API in argillaceous very fine to fine-grain crevasse-splay sandstones. A corresponding change also occurs in sonic-log response from 90–100 to 80–90&nbsp;µsft<sup>–1</sup>. Crevasse-splay deposits are characterized by gradationally based upwards-decreasing log responses with sharp inflections at the upper contact with overlying coal seams or lake or marine mudstones.
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Facies Oc is characterized by very erratic gamma-ray and sonic-log responses, reflecting the variable interbedding of lithologies. Gamma-log response increases from 120–>150API in the underlying facies Ol mudstones–siltstones to 75–105API in argillaceous very fine to fine-grain crevasse-splay sandstones. A corresponding change also occurs in sonic-log response from 90–100 to 80–90µsft<sup>–1</sup>. Crevasse-splay deposits are characterized by gradationally based upwards-decreasing log responses with sharp inflections at the upper contact with overlying coal seams or lake or marine mudstones.
  
 
=== Facies Ol – Lake and marine-bay deposits ===
 
=== Facies Ol – Lake and marine-bay deposits ===
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==== Description ====
 
==== Description ====
  
Lake and marine-bay deposits consist essentially of blocky, dark grey to black mudstones and siltstones, which may contain either freshwater or marine faunas. Thin very fine-grained sandstones and nodular horizons are interbedded locally in places. Deposits range in thickness from a few tens of centimetres to exceptionally 15–20&nbsp;m, with an average thickness in the range 2–10&nbsp;m. The main sedimentary structure is parallel lamination; however, convoluting and bioturbation may also occur in places. Lake and marine-bay deposits almost invariably overlie swamp or flood-plain sediments (facies Os) with a sharp contact, and are overlain gradationally by either crevasse splay (facies Oc) or distributary mouth-bar (facies Cd) sediments.
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Lake and marine-bay deposits consist essentially of blocky, dark grey to black mudstones and siltstones, which may contain either freshwater or marine faunas. Thin very fine-grained sandstones and nodular horizons are interbedded locally in places. Deposits range in thickness from a few tens of centimetres to exceptionally 15–20m, with an average thickness in the range 2–10m. The main sedimentary structure is parallel lamination; however, convoluting and bioturbation may also occur in places. Lake and marine-bay deposits almost invariably overlie swamp or flood-plain sediments (facies Os) with a sharp contact, and are overlain gradationally by either crevasse splay (facies Oc) or distributary mouth-bar (facies Cd) sediments.
  
 
==== Interpretation ====
 
==== Interpretation ====

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