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Petrology and diagenetic history of the upper shale member of the Late Devonian–Early Mississippian Bakken Formation, Williston Basin, North Dakota

By
Neil S. Fishman
Neil S. Fishman
U.S. Geological Survey, Denver, Colorado, USA
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Sven O. Egenhoff
Sven O. Egenhoff
Department of Geosciences, Colorado State University, 322 Natural Resources Building, Fort Collins, Colorado 80523-1482, USA
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Adam R. Boehlke
Adam R. Boehlke
U.S. Geological Survey, Denver Federal Center, Lakewood, Colorado 80225, USA
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Heather A. Lowers
Heather A. Lowers
U.S. Geological Survey, Denver Federal Center, Lakewood, Colorado 80225, USA
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Published:
September 01, 2015

The organic-rich upper shale member of the upper Devonian–lower Mississippian Bakken Formation (Williston Basin, North Dakota, USA) has undergone significant diagenetic alteration, irrespective of catagenesis related to hydrocarbon generation. Alteration includes precipitation of numerous cements, replacement of both detrital and authigenic minerals, multiple episodes of fracturing, and compaction. Quartz authigenesis occurred throughout much of the member, and is represented by multiple generations of microcrystalline quartz. Chalcedonic quartz fills radiolarian microfossils and is present in the matrix. Sulfide minerals include pyrite and sphalerite. Carbonate diagenesis is volumetrically minor and includes thin dolomite overgrowths and calcite cement. At least two generations of fractures are observed.

Based on the authigenic minerals and their relative timing of formation, the evolution of pore waters can be postulated. Dolomite and calcite resulted from early postdepositional aerobic oxidation of some of the abundant organic material in the formation. Following aerobic oxidation, conditions became anoxic and sulfide minerals precipitated. Transformation of the originally opaline tests of radiolaria resulted in precipitation of quartz, and quartz authigenesis is most common in more distal parts of the depositional basin where radiolaria were abundant.

Because quartz authigenesis is related to the distribution of radiolaria, there is a link between diagenesis and depositional environment. Furthermore, much of the diagenesis in the upper shale member preceded hydrocarbon generation, so early postdepositional processes were responsible for occlusion of significant original porosity in the member. Thus, diagenetic mineral precipitation was at least partly responsible for the limited ability of these mudstones to provide porosity for storage of hydrocarbons.

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Daniel Larsen
Daniel Larsen
Department of Earth Sciences, University of Memphis, Memphis, Tennessee 38152, USA
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Sven O. Egenhoff
Sven O. Egenhoff
Department of Geosciences, Colorado State University, 322 Natural Resources Building, Fort Collins, Colorado 80523-1482, USA
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Neil S. Fishman
Neil S. Fishman
U.S. Geological Survey, Denver, Colorado, USA
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Hess Corporation
Hess Corporation
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Geological Society of America
Volume
515
ISBN print:
9780813725154
Publication date:
September 01, 2015

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