Organic facies in black shale of Devonian-Mississippian Bakken Formation, southeastern Saskatchewan

Alginite, acritarch and sporinite macerals in the epicontinental black shale of the Devonian-Mississippian Bakken Formation in southeastern Saskatchewan have been studied with fluorescence incident light microscopy to evaluate the petrographic organic facies. Three organic facies have been defined for the upper and lower shale members of the Bakken Formation: (i) organic facies A is characterized by abundant, relatively large Prasinophyte alginites; (ii)organic facies B is characterized by small acanthomorphic acritarchs and small Prasinophyte alginite, sporinite may be present; and (iii) organic facies C contains macerals similar to organic facies B, sporinites and floral inertinite. Based on the distribution of macerals across a typical Devonian to Mississippian shelf, organic facies in the Bakken shale are interpreted to reflect the degee of water column agitation increasing from the organic facies A setting to the organic facies B and C settings. The lower shale member is dominated by organic facies A except for isolated pockets of organic facies B suggesting a more agitated water colum. The organic facies distribution in the upper shale is markedly different consisting of organic facies A in the west and organic facies B in the east.