Date of Award

1994

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

N.F. Forsman

Abstract

The purpose of this study was to determine if enough evidence exists to support an impact origin hypothesis the Newporte structure. Newporte, a petroliferous, subsurface, crater-shaped feature is located one mile south of the North Dakota - Saskatchewan border in Renville County. It is evident in Precambrian through Ordovician strata at depths of 9100 to 9600 ft (2774 to 2926 m) structure is approximately 2.0 miles (J.2 km) in diameter. Shell Oil company discovered Newporte field when testing this seismically-defined structure in 1977.

Seismic reflection profiling data and synthetic seismograms were used to generate maps that confirmed the circularity of the structure. Because no wells have been drilled in the central region of the structure, the seismic data were necessary for mapping and interpreting the morphology of the feature. Wireline logs of the seven wells, all located on the remaining rim, were used to identify lithologic units, verify the seismic data, and they were used in an attempt to interpret the age of the Newporte structure. All available well cores were described (Appendix B), and nearly 140 thin sections were evaluated microscopic evidence of shock metamorphism.

Interpretation of seismic data reveals a crater with a distinctive raised rim, and what may be vestiges of a central uplift. Intriguing breccias, resembling impact breccia, have been described from three well cores. Several examples of unusual microscopic features, perhaps indicative of low shock pressures, were discovered in quartz from sandstone and brecciated crystalline rock from the Mott 14 34 well. It has been concluded in this study, based on geophysical data, well core samples, and a thorough microscopic evaluation that there is much evidence to support an impact origin for the Newporte structure. The presence of a Deadwood breccia interval suggests the impact event may have occurred during or after Deadwood deposition, prior to deposition of the Winnipeg Group (Late Cambrian to Early Ordovician, or prior to Late Ordovician)

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