ABSTRACT

The Newporte structure, a petroliferous, subsurface, impact crater is located in Renville County, about one mile south of the North Dakota-Saskatchewan border. Reflection seismic data indicate that the feature is characterized by a structurally low central crater and a raised peripheral rim. Petroleum has been produced from wells that were drilled into the raised rim. One of these wells, Shell 14-34 Mott, is thought to be the only Precambrian producer in the Williston Basin.

In order to establish an impact origin for the Newporte structure, we examined all available core, 150 thin sections, wireline logs, and reflection seismic data. The cores help to establish the presence of impact breccias in the Ordovician through Precambrian section at depths of 9100-9600 ft (2774-2926 m). The distribution of these brecciated strata indicates that impact occurred during deposition of the Deadwood Formation (late Cambrian to early Ordovician). The thin sections show evidence of shock metamorphism, including planar deformation features (PDF) in quartz and feldspar grains, and support the impact origin theory. The wireline logs were used to identify subsurface lithologic units and constrain the interpretation of the available seismic data. The interpretation of the seismic reflection profiles allowed for the mapping of the Newporte structure in interwell areas. These data demonstrate convincingly that the Newporte structure is an impact crater of late Cambrian to early Ordovician age.