Sedimentology of Fraser River Delta Peat Deposits: A Modern Analogue for Some Deltaic Coals

  1. R. A. Rahmani and
  2. R. M. Flores
  1. W. B. Styan and
  2. R. M. Bustin

Published Online: 28 APR 2009

DOI: 10.1002/9781444303797.ch14

Sedimentology of Coal and Coal-Bearing Sequences

Sedimentology of Coal and Coal-Bearing Sequences

How to Cite

Styan, W. B. and Bustin, R. M. (1985) Sedimentology of Fraser River Delta Peat Deposits: A Modern Analogue for Some Deltaic Coals, in Sedimentology of Coal and Coal-Bearing Sequences (eds R. A. Rahmani and R. M. Flores), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303797.ch14

Author Information

  1. Department of Geological Sciences, The University of British Columbia, Vancouver, B.C. V6T 2B4, Canada

  1. Shell Canada Resources, Calgary, Alta T2P 2H5, Canada

  1. Reprinted from International Journal of Coal Geology, 3 (1983), 101–143, courtesy of Elsevier Science Publishers.

Publication History

  1. Published Online: 28 APR 2009
  2. Published Print: 26 MAR 1985

ISBN Information

Print ISBN: 9780632012862

Online ISBN: 9781444303797

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Keywords:

  • sedimentology of Fraser River delta peat deposits – a modern analogue for some deltaic coals;
  • distal lower delta plain;
  • alluvial plain;
  • Lulu island;
  • fire splays

Summary

On the Recent lobe of the Fraser River delta peat accumulation has actively occurred on the distal lower delta plain, the transition between upper and lower delta plains, and the alluvial plain.

Distal lower delta plain peats developed from widespread salt and brackish marshes and were not influenced appreciably by fluvial activity. Lateral development of the marsh facies were controlled by compaction and eustatic sea-level rise. The resulting thin, discontinuous peat network contains numerous silty clay partings and high concentrations of sulphur. Freshwater marsh facies formed but were later in part eroded and altered by transgressing marine waters. The peats overlie a thin, fluvial, fining-upward sequence which in turn overlies a thick, coarsening-upward, prodelta–delta front succession.

Lower delta plain–upper delta plain peats initially developed from interdistributary brackish marshes and were later fluvially influenced as the delta prograded. The thickest peats occur in areas where distributary channels were abandoned earliest. Sphagnum biofacies replace sedge-grass-dominated communities except along active channel margins, where the sedge-grass facies is intercalated with overbank and splay deposits. The peats are underlain by a relatively thin sequence of fluvial deposits which in turn is underlain by a major coarsening-upward delta front and pro-delta sequence.

Alluvial plain peats accumulated in back swamp environments of the flood plain. Earliest sedge-clay and gyttja peats developed over thin fining-upward fluvial cycles or are interlaminated with fine-grained flood deposits. Thickest accumulations occur where peat fills small avulsed flood channels. Overlying sedge-grass and Sphagnum biofacies are horizontally stratified and commonly have sharp boundaries with fine-grained flood sediments. At active channel margins, however, sedge-grass peats are intercalated with natural levée deposits consisting of silty clay. These levée reduce both the number and size of crevasse splay deposits.

Coal originating from peats of the different environments of the Fraser River delta would vary markedly in character. Peats of the lower delta plain will form thin lenticular coal seams with numerous splits and have a high ash and sulphur content. Peats from the lower to upper delta plain will be laterally extensive and of variable thickness and quality. Basal portions of the seams will contain numerous splits and have a high sulphur content where as upper portions will be of higher quality. Peats from the upper delta plain–alluvial plain will form thick, isolated and laterally restricted coal seams characterized by low ash and sulphur contents.