Date of Award
Master of Science (MS)
Thirty-three oil well cores were examined and approximately 3,100 oil well logs were used to determine the depositional environments of the Tyler Formation (Pennsylvanian) in northwestern North Dakota. Ninety sandstone thin-sections were described and twenty-nine sandstone samples were analyzed by scanning electron microscope/X-ray microanalysis techniques to characterize sandstone diagenesis.
The Tyler Formation in northwestern North Dakota is correlative with the lower unit of the Tyler Formation in southwestern North Dakota. The upper unit of the Tyler Formation in southwestern North Dakota is not present in northwestern North Dakota, contrary to previous workers suggestions. The Tyler Formation in northwestern North Dakota consists of varicolored mudstone, medium-gray claystone, thin bituminous coal beds, dark-gray shale and limestone, and gray sandstone. The upper unit of the Tyler Formation in southwestern North Dakota consists of gray sandstone, dark-gray limestone and shale, and varicolored mudstone.
Lenticular sandstones present in the middle and rarely at the base of the formation, which occur in northeast-southwest linear trends, indicate that the Tyler Formation in northwestern North Dakota was deposited as a river channel system on a low-lying, prograding coastal plain. Depositional environments associated with the coastal plain include river channels, flood plains, lakes, estuaries, caliche paleosols, and backswamps. Throughout deposition of the Tyler Formation, several major river channels flowed in a predominantly southwest direction across a low-lying coastal plain and transported quartz sand toward a delta or shoreline, not identified in this study, at the margin of a shallow epeiric sea.
Initially, the presence of detrital clay and infiltration clay and early hematite and chlorite coatings on quartz grains was the most important factor influencing porosity reduction in Tyler sandstones. The first major diagenetic event responsible for porosity reduction was the development of authigenic quartz overgrowths. Other cements that have contributed to porosity reduction in Tyler sandstones include amorphous silica (opal), calcite, ankerite, siderite, anhydrite, barite, hematite, and pyrite, In addition, authigenic kaolinite, illite, and chlorite have reduced porosity in Tyler sandstones. Dissolution of carbonate cement resulted in the formation of secondary porosity.
Sandstone diagenesis took place shortly after sand was deposited in a marine environment, while sediments were being flushed with meteoric ground water, and while sands were being flushed with chemically evolved pore water released after diagenesis and compaction of interbedded mud-rich sequences.
River-channel sandstones in northwestern and southwestern North Dakota and barrier-island sandstones present only in southwestern North Dakota contain considerable amounts of intergranular porosity. Petroliferous sandstones in southwestern North Dakota are fine- to medium-grained, well-sorted, texturally mature quartzarenites. Preservation of porosity is related to depositional and diagenetic processes.
Quandt, Larry R., "Depositional environments and sandstone diagenesis in the Tyler Formation (Pennsylvanian), western North Dakota" (1990). Theses and Dissertations. 235.