Lacustrine-Interdeltaic Coal in the Fort Union Formation (Palaeocene), Powder River Basin, Wyoming and Montana, U.S.A.

  1. R. A. Rahmani and
  2. R. M. Flores
  1. W. B. Ayers Jr and
  2. W. R. Kaiser

Published Online: 28 APR 2009

DOI: 10.1002/9781444303797.ch4

Sedimentology of Coal and Coal-Bearing Sequences

Sedimentology of Coal and Coal-Bearing Sequences

How to Cite

Ayers, W. B. and Kaiser, W. R. (1985) Lacustrine-Interdeltaic Coal in the Fort Union Formation (Palaeocene), Powder River Basin, Wyoming and Montana, U.S.A., 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.ch4

Author Information

  1. The University of Texas at Austin, Bureau of Economic Geology, Austin, Texas 78712, USA

  1. Publication authorized by the Director, Bureau of Economic Geology, The University of Texas at Austin.

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:

  • Lacustrine-interdeltaic coal in Fort Union Formation - Powder River Basin;
  • Tongue River Member of Union Formation, major coal-bearing unit in River Basin of Wyoming;
  • Powder River Basin, region of low topographic relief;
  • major-sand maps, delineating sand body geometry;
  • lacustrine-interdeltaic model, explaining framework-peat relationship

Summary

The Tongue River Member of the Fort Union Formation, the major coal-bearing unit in the Powder River Basin of Wyoming and Montana, records a history of paludal, fluvial-deltaic, and lacustrine sedimentation. Tongue River deltas filled the basin primarily from the eastern margin as they prograded into a lake (Lebo Shale Member) which occupied the basin axis. Major streams entered the Fort Union coastal plain from point sources, resulting in areas of broad interdeltaic coastal plain isolated from major clastic influx.

We mapped the principal clastic facies and the regional distribution of thick Tongue River coal seams using approximately 1,400 induction-electric logs. A detailed study of a thick coal seam in the centre of the basin shows that coal occurrence is facies-dependent. Peat accumulation began in interdeltaic and interdistributary areas at the loci of regional ground-water discharge. Upon delta abandonment, peat swamps overspread the abandoned lobes. The result is a thick, strike-parallel, interdeltaic coal seam bounded by fluvial-deltaic framework facies. The depositional model and coal-occurrence maps provide a guide for coal exploration and a model for interpreting individual deposits in the Powder River Basin.