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Geological | Coal >  Formation

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Coal formation:

when:

North European principle coalfields:-

  • era - Upper Palaeozoic
    • period - Carboniferous
      • epoch - Upper Carboniferous / Silesian
        • age - Westphalian & Stephanian
  • dates:
    • Carboniferous :              345 - 280 my bp
      • Silesian :                 325 -280 my bp
        • Westphalian
          • A :
          • B :
          • C :
          • D :
        • Stephanian :

how:

first by peat formation

  • formed in vast coastal swamps containing jungle-like vegetation
  • modern analagous locations eg Florida Everglades
  • ancient swamps dominated by large scaly-barked trees (lycopsids)
    • club-mosses and horsetails 45 - 60 ft (15 -20m)
  • dead vegetation protected from total decay by submergence in water
    • compression from overlying material forms peat
    • aerobic bacterial activity near surface
      • water stagnant, oxygen consumed & decay stops
    • anaerobic bacterial activity raises acidity of water
      • ph reaches 4.0 & decay stops
    • deepest layers of peat transformed into gytta
      • gytta : black cheesy jell-like substance
      • gytta will undergo metamorphism to form coal
    • requires large quantities of vegetation to form thick seams
    • but does not require large thickness of peat
  • subsequent burial by sediments protects from erosion
    •  

then by coalification

  • bituminisation
    • deeper burial + geothermal gradient starts bituminisation
    • gradual escape of more volatile hydrocarbon compounds
    • increased burial and compaction produces higher rank of coal
      • lignite / brown coal
      • sub-bituminous
      • bituminous
  • metamorphism
    • subsequent low-grade pressure metamorphism produces
      • sub-anthracite
      • anthracite

where:

  • the palaeoenvironment:
    • non-marine flora and fauna
    • fossil seeds show adaptations for dispersal by water
  • the palaeoclimate:
    • considered to be a tropical one -
      • very warm and humid conditions deduced from:
        • presence of cold-blooded animals
        • nature of vegetation
      • Carboniferous trees lack growth rings indicating:
        • lack of distinct seasonal changes.
  • the palaeogeography:
    • palaeomagnetic data shows North-European land mass near equator
    • part of a much larger land mass (Laurasia)
      • N America + N Europe + N Asia
    • Lower Carboniferous  (Dinantian)
      • NW Europe:
        • clear shallow warm sea - limestone formation;
      • in UK Pennine area: 
        • localised stable blocks  -
          • Askrig-Alston and Derbyshire
        • & subsiding basins -
          • Northumberland and Mid-Pennine troughs
        • limestone formation on stable blocks
        • repeated sandstone - shale formations in basins
    • Early Upper Carboniferous (Namurian)
      • in UK Pennine area:
        • recurrent deltaic formation and infilling of the deeper basins
        • rhythmic succession of mudstones and sandstones
    • Later Upper Carboniferous (Silesian)
      • in UK Pennine area:
        • deltas are extensive and established
        • large areas flat & low-lying
        • coastal swamps
        • recurrent / rhythmic subsidence

    upperCarb-m02

                   

    • End Carboniferous
      • NW Europe:
        • Variscan orogony
      • in UK Pennine area:
        • folding, faulting
        • uplift & erosion
  • the palaeotectonic activity:
    • cyclic deposition over vast areas
      • short geological time scales
      • alternation of marine and non-marine deposits
      • possible causes:
        • eustatic (worldwide) sea level changes
          • Gondwanaland glaciation cycles
          • large scale deep-sea floor warping
        • intermittent regional subsidence
        • local effects due to fluctuations in clastic sediment supply
    • Variscan orogony
      • Afro plate -> Euro plate
      • faulting & thrusting in S England & Wales
      • folding & faulting in N England & Scotland
      • uplift & erosion

    what happened next:

    • Permian
      • extensive shallow inland sea (Zechstein)
        • deposition of marls, limestones, dolomites

      zechstein-a-m

    what happened later

  • the Mesozoic:
    • Triassic
      • desert conditions
      • aeolian sands and pebble beds
    • Jurasic
      • TBD
    • Cretacious
      • TBD
  • the Cenozoic:
    • Tertiary
      • TBD
    • Quaternary
      • TBD

     

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    05 May, 2009

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    11:33:04 AM

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