Coal Deposition in an Anastomosing-Fluvial System: The Pennsylvanian Cumberland Group South of Joggins, Nova Scotia, Canada

  1. R. A. Rahmani and
  2. R. M. Flores
  1. Brian R. Rust1,
  2. Martin R. Gibling2 and
  3. Andrew S. Legun3

Published Online: 28 APR 2009

DOI: 10.1002/9781444303797.ch6

Sedimentology of Coal and Coal-Bearing Sequences

Sedimentology of Coal and Coal-Bearing Sequences

How to Cite

Rust, B. R., Gibling, M. R. and Legun, A. S. (1985) Coal Deposition in an Anastomosing-Fluvial System: The Pennsylvanian Cumberland Group South of Joggins, Nova Scotia, Canada, 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.ch6

Author Information

  1. 1

    Geology Department, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada

  2. 2

    Geology Department, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada

  3. 3

    Ministry of Energy, Mines and Petroleum Resources, P.O. Box 7438, Fort St John, British Columbia V1J 4M9, Canada

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:

  • coal deposition in anastomosing-fluvial system - Pennsylvanian Cumberland Group;
  • Pennsylvanian Cumberland Group south of Joggins - alluvial succession, containing channel sandstones and overbank deposits;
  • overbank deposits, comprising levée and abundant crevasse-splay sandstones;
  • floodbasin deposits, comprising grey to red mudrocks;
  • McCarren Creek succession, accumulating on alluvial plain

Summary

The Pennsylvanian Cumberland Group south of Joggins, Nova Scotia, is an alluvial succession containing channel sandstones and overbank deposits comprising mudrocks, coals and thin sheet sandstones. The section between McCarren Creek and Ragged Reef Point includes a 600 m coarsening-up sequence in which channel sandstones increase in abundance upwards.

The channel sandstones in the lower 500 m of this sequence have limited lateral extent, stepped bases and numerous subhorizontal internal erosion surfaces. Commonly they have sharp tops, and neither fine upwards, nor show upward decrease in the scale of sedimentary structures. Lateral-accretion strata occur only in the upper parts of a few channel fills. The channel sandstones are attributed to vertical accretion in anastomosing channels, accompanied by some widening and lateral migration, terminating with avulsion. In the uppermost 100 m of the sequence an increase in the lateral extent and density of the channel sandstones is attributed to the transition between anastomosing and meandering channel patterns.

Overbank deposits comprise levée and abundant crevasse-splay sandstones, which form thin sheets transitional upward, downward and laterally into floodbasin mudrocks. Levée sandstones characteristically coarsen upward and bear upright tree trunks. Crevasse-splay sandstones fine upwards or coarsen then fine upwards. Floodbasin deposits comprise grey to red mudrocks, rooted carbonaceous shales and coal seams. Red colouration increases up-section, as coal seams disappear and channel sandstones become more abundant. This is attributed to tectonic steepening of the alluvial plain, which lowered water-tables and increased the amount and grain size of the transported sediment. The lack of thick coal seams is attributed to low water-tables and to frequent progradation of crevasse-splays over swamps, as a result of locally rapid basin subsidence.