ABSTRACT

A study of the coal-bearing Albian Gates Formation (Falher equivalent) in northeastern British Columbia was undertaken in order to ascertain the factors controlling coal facies variation, as well as to obtain a better understanding of gas generation and retention capacity in the coals. Lithotype (coal facies) samples collected from mines and coal and petroleum drill core were analysed for maceral composition. Compositional boundaries between lithotypes are gradational. From bright to dull coals, there is a progressive decrease in vitrinite and increase in inertinite; liptinite is negligible (<1%). Compositional differences between lithotypes reflect differences in vegetational characteristics, accumulation rate and decomposition rate of wetland plant communities. Lateral and vertical variation in composition was controlled by groundwater levels (due to sea level variations and climatic conditions?) and proximity to active fluvial systems. The lithotypes represent depositional environments ranging from forest swamps to dry, herbaceous and/or shrubby marshes. Swamps were dominated by coniferous trees with a significant component of ferns as herbs or low trees. Angiosperms and cycads contributed to the vegetation in the form of shrubs. Angiosperms were probably also present as marginal herbs.

A representative suite of lithotype samples was analysed for surface area. Differences in maceral composition of the individual lithotypes is believed to be an important control on the differences in surface area. Determining the controls on coal facies variations (compositional variations) is important in understanding variations in the gas generation and retention capacity of coals.

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