| Summary: | The Upper Viséan to Namurian Mabou Group of Cape Breton Island conformably overlies highest marine carbonate strata of the Windsor Group and unconformably (? also conformably) underlies the mainly fluviatile Cumberland Group. Regionally, the Mabou Group, dominated by fine grained clastic rocks, comprises a lower grey facies assemblage of proposed lacustrine origin, and an upper red facies of fluviatile origin. The grey facies is represented by the Hastings Formation in western Cape Breton Island, by the Cape Dauphin Formation in the Sydney Basin, and by the lower parts of the MacKeigan Lake Formation in the Loch Lomond Basin of southeastern Cape Breton Island. The red facies comprises the Pomquet Formation in western Cape Breton Island, the Point Edward formation in the Sydney Basin, and the upper part of the MacKeigan Lake Formation. The ubiquitous presence of thin, laterally discontinuous limestone beds in the lower grey facies of the Mabou Group is a useful guide to stratigraphic position. These carbonate beds include wackestones and grainstones containing intraclasts and ooids as well as ostracods and serpulids. Stromatolites are the most common carbonate rock type within the grey facies of the Mabou Group. Faunal elements characteristic of normal marine environments are conspicuously absent. The carbonate rocks and associated siliciclastic sediments indicate that deposition of the Mabou Group grey facies occurred within a shallow subaqueous environment undergoing intermittent periods of sub-aerial exposure, a setting consistent with lacustrine conditions, traditionally postulated for lower Mabou Group sedimentation. Initially elevated salinities reflecting the last stages of marine evaporite sedimentation gave way progressively to brackish and then fresh-water conditions as the Late Viséan arid climate moderated during earliest Namurian time. RÉSUMÉ Le Groupe du Viséen supérieur au Namurien de Mabou, sur l'ile du Cap-Breton, recouvre de façon ...
|
|---|