Sedimentary Environments of the Ardley Coal Zone

The Ardley Coal Zone at the top of the Scollard Formation is associated with alluvial plain/fluvial sediments (Richardson et al., 1988). Widespread swamps and very low flow gradients characterize the alluvial plain environment. The moderately low ash content, and the laterally persistent and relatively thick nature of many of these coal seams, suggests the development of widespread swamps isolated from clastic deposition for long periods.

There are two thick, sandy fluvial channels present in the succession: a lower channel and an upper channel. The lower channel splits the Lower Ardley Coal Zone into two parts in the central part of the study area. The thickest sandstone body is about 15 m thick. The fluvial channel produced a ribbon sandstone along a northwest-southeast direction (see Figure 14: Cumulative sandstone (m) of the Lower Ardley Coal Zone) parallel to the general strike of the Western Canada Sedimentary Basin , with a minor arm of the ribbon trending to the east. The upper channel represents the depositional interval between the Lower and Upper Ardley coal zones. The thickest sandstone body is about 20 m thick. Channel sandstone forms a sinuous ribbon along a north-south direction, about 70° from the Lower Ardley channel direction (see Figure 13: Cumulative sandstone (m) between Lower and Upper Ardley Coal zones).

The grading upwards from sandstone to layers of very fine-grained sandstone and siltstone or shales may indicate rapid deceleration of flow into very shallow standing bodies of water. The generally abrupt transition from peats to channel fills resulted from a sudden improvement in drainage conditions at the site of deposition. This was achieved by the progradation of well-drained floodplain areas over poorly drained alluvial backswamps. The coals were probably formed in swamps affected by temporary river discharge fluctuations. The river-floodplain influence results in higher mineral-matter contents of the peats.

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Last modified: May 7, 2008