The "Mammoth" coal seam in southeastern British Columbia, Canada, was structurally thickened to 100 m as a result of Laramide folding and faulting. Samples from the coal seam, examined using reflected-light microscopy, include thermally altered coal macerals, their by-products (e.g., pyrolytic carbon), and, in addition, heat-affected preoxidized coke.The heat-affected residues are composed of material formed by friction produced from faulting of the coal-bearing strata. The pyrolytic carbon was formed from the distillation of coal and from coal tar pitch.The occurrence of preoxidized, heat-affected vitrinite suggests that the Mammoth coal seam was oxidized before faulting.

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