Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

M. Rich


This investigation is a petrographic study of a composite section from the Duperow formation in western North Dakota in which seven cyclic microfacies are described and environmentally evaluated. The microfacies are:

1. Anhydrite-dolomite microfacies. Chemically precipitated cryptocrystalline calcite.

2. Micrite microfacies: Chemically precipitated, structurless cryptocrystalline calcite.

3. Saccharoidal dolomite microfacies. Microgranulor dolomite representin dolonitized limestone .

4. Pelmicrite-pelletiferous micrite microfacies. Pelletoidal grains of cryptocrystalline calcite and small amounts of fossil material in a matrix of cryptocrystalline calcite.

5. Fossiliferous micrite-biomicrite microfacies. Fossil material in a matrix of cryptocrystalline calcite.

6. Pelsparite microfacies. A loo e framework of pelletoidal grains and rounded fossil fragments cemented by sparry calcite.

7. Biolithite microfacies. Stromatoporoid constructed limestone.

The Duperow formation is believed to represent sedimentation over a very broad, shallow water area in a warm, arid climate. A similarity between the Duperow sediments and the sediments presently forming in the Bahamas is noted. The chemically precipitated sediments were formed in shoreward areas, possibly in isolated lagoons or ponds. Sediments represented by the pelmicirte-pelletiferous micrite microfacies were deposited in shallow, gently agitated waters which extended seaward from the area of evaporite formation. At the transition between shallow and deep water, a high energy environment was developed in which bars of pelletal material (pelsparite microfacies) and reefoid structures (biolithite microfacies) were developed. Sediments represented by the fossiliferous micrite-biomicrite microfacies were formed in protected areas adjacent to the bars and reefoid structures.

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