Basin Facies Analysis of Coal-Rich Tertiary Fluvial Deposits, Northern Powder River Basin, Montana and Wyoming

  1. J. D. Collinson and
  2. J. Lewin
  1. Romeo M. Flores

Published Online: 29 APR 2009

DOI: 10.1002/9781444303773.ch40

Modern and Ancient Fluvial Systems

Modern and Ancient Fluvial Systems

How to Cite

Flores, R. M. (1983) Basin Facies Analysis of Coal-Rich Tertiary Fluvial Deposits, Northern Powder River Basin, Montana and Wyoming, in Modern and Ancient Fluvial Systems (eds J. D. Collinson and J. Lewin), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303773.ch40

Author Information

  1. U.S. Geological Survey, Denver, Colorado 80225, USA

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 7 FEB 1983

ISBN Information

Print ISBN: 9780632009978

Online ISBN: 9781444303773

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Keywords:

  • basin facies analysis of coal-rich tertiary fluvial deposits – northern Powder River basin, Montana and Wyoming;
  • tertiary coal deposits;
  • detrital deposits;
  • palaeogeographic reconstruction;
  • alluvial-plain setting

Summary

Facies analysis of the Palaeocene Tongue River Member of the Fort Union Formation in the northern Powder River Basin provided an understanding of the origin of associated thick coal deposits. Lithostratigraphic synthesis of the lower part of the Tongue River Member recognized coals associated with meander belt and lacustrine–floodplain lithofacies. The meander belt lithofacies is characterized by a high density of closely spaced channel sandstones and abandoned channel deposits, interspersed with subordinate levée deposits. This lithofacies grades laterally and alternates vertically with the lacustrine–floodplain lithofacies that consists of crevasse-splay and crevasse delta–lake deposits. Associated with both of these lithofacies is the backswamp lithofacies that consists of coal beds (as much as 20 m in thickness) and carbonaceous shales. The accumulation of thick coals was controlled by the following interrelated factors: localized aggradation of fluvial channels, subsidence due to basement tectonic control and differential compaction of sediments, length of time of peat accumulation, nature of the backswamp's palaeoflora, and palaeoclimate. These factors were present in an alluvial plain that was situated in an intermontane basin. The alluvial plain contained a north-eastward flowing trunk–tributary system that drained into the Cannonball Sea.