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Three Westphalian D cyclothems were studied from the coal-bearing Sydney Mines Formation, Cape Breton Island, Nova Scotia. Allogenic (glacioeustatic?) processes, and superimposed autogenic processes, were responsible for cyclothem facies successions: 1) lake/bay-fill and distributary channel, 2) well-drained floodplain, 3) poorly-drained floodplain to coastal plain and 4) extensive mire. Major coal seems, organic-rich limestone/shale units, red mudstone and nodular carbonate layers are laterally extensive which suggests regional controls on their formation.

The Backpit seam and limestone/shale roof unit (top of Cyclothem 2) contain a detailed record of basinal processes over an extended period. The Backpit seam is a high volatile B to A bituminous coal (Ro = 0.69-0.76%), with moderate to high ash (avg. 15.3 + 6%) and sulphur (avg. 5.2 + 2%). Banded lithotypes constitute a major portion of the seam; vitrinite macerals and vitrinite-rich microlithotypes predominate. Distinct fusain bands are common and represent the charred remains of ancient fires. Some dull to coaly shale layers can be correlated across the onshore portion of the basin for more than 45 km.

The Backpit peat accumulated in a rheotrophic mire, elongated parallel to depositional strike. Coal facies patterns indicate a wetting upward trend in the upper portion of the seam that culminated in the flooding of the mire and the formation of a broad, shallow lake or bay. Agglutinated foraminifera extracted from the underclay and the roof strata support a coastal setting for the mire. The abundance of fresh to brackish tolerant fauna such as bivalves, ostracods, serpulids, sharks and other fish in the Backpit roof unit and the paucity of open marine fauna suggest that the area was protected from open marine inundation.

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