a The age of the “Newporte event” has been estimated on biostratigraphic grounds at late-Deadwood, around 500 Ma, which places the formation of the Newporte structure after the formation of the intracratonic Williston Basin at around 550 Ma (Baird et al., 1995).
Petrographic study of Newporte rocks revealed shocked quartz and K-feldspar grains with PDFs in several thin sections of breccias. Most quartz grains with PDFs were observed in granit-derived quartz or in granite fragments. These findings confirm that Newporte is an impact structure (Koeberl et al, 1995).
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.(Gerlach et al, 1995).
Baird D.J., Knapp J. H., Steer D.N., Brown L.D. and Nelson K.D. (1995) Upper-mantle reflectivity beneath the Williston basin, phase-change Moho, an the origin of intracratonic basins.Geology 23, 431-434.
Forsman, N. F., T. R. Gerlach, and N. L. Anderson (1996), Impact origin of the Newporte structure, Williston basin, North Dakota, AAPG bulletin, 80(5), 721-730.
Gerlach T.R. The Newporte Structure: a Petroliferous, Subsurface Impact Crater, Renville County, North Dakota GF Activation Technologies, Grand Forks, North Dakota 58203 and the Energy & Environmental, Research Center, University of North Dakota, Grand Forks, North Dakota 58202 (1995)
Koeberl, C., Reimold, W. U., & Brandt, D. The Newporte Impact Structure, North Dakota: Shock Metamorphism in Breccias Abstracts of the Lunar and Planetary Science Conference, volume 26, page 773, (1995)
Christian Koeberl, Wolf Uwe Reimold, The Newporte impact structure, North Dakota, USA Geochimica et Cosmochimica Acta Volume 59, Issue 22, November 1995, Pages 4747–4767 University of New Brunswick, 2012.