Sedimentology of the coal-bearing Mist Mountain Formation, Line Creek, Southern Canadian Cordillera: relationships to coal quality

A detailed sedimentological investigation of the Jurassic-Cretaceous Mist M ountain Formation in the southern Canadian Cordillera was undertaken to det ermine what, if any, sedimentological factors control coal quality and seam geometry. In the Line Creek area, the Mist Mountain Formation is divisible into two units based on abundance and lateral continuity of facies. The lo wer unit consists of alternating laterally extensive coal seams and thick, widespread channel sandstones interspersed with crevasse splay and flood pl ain facies sediments. The lower unit was deposited in an interdeltaic coast al plain environment protected from marine incursion by the beach ridge-dun e sandstones of the underlying Morissey Formation. The upper unit of the Mi st Mountain Formation was deposited in a distal alluvial-fluvial flood plai n environment and has similar facies to the lower unit but coal seams and c hannel sandstones are less laterally continuous and thinner than in the low er unit. Channel sandstones decrease in number and thickness up-section, an d are replaced by an increasing abundance of coal Seams, flood plain and cr evasse splay facies sediments. Seam geometry and ash data indicate that ela stic sedimentation had only Limited influence on pear (coal) accumulation i n the Mist Mountain Formation. While the geometry of the seams reflects the proximity of under- and overlying channel sandstones, neither abundance no r mineralogy of the coal ash reflects changes in surrounding elastic sedime nts. The Mist Mountain Formation peat mires were thus not obviously influen ced by coeval fluvial activity. Characteristics of the lower unit suggest p ear mires developed only during hiatus in elastic deposition, whereas upper unit coals appear to have formed in at least partially domed mires contemp oraneous with elastic sedimentation. The vitrinite content:of the coal incr eases up-section at the expense of semifusinite, possibly reflecting an inc rease in the proportion of arborescent vegetation in the mire with time and a lower susceptibility to fires. (C) 2000 Elsevier Science B.V. All rights reserved.