CLOUD CREEK IMPACT STRUCTURE
by: Charles O’Dale
- Type: Complex
- Age Ma: ~190 +/- 30 a – JURASSIC
- Diameter: 7 km
- Location: N 43° 7’ W 106° 45’
- Shock Metamorphism: Planar deformation features (PDFs) in quartz
a The Cloud Creek structure is dated chronostratigraphicly, formed sometime between the Late Triassic and Middle Jurassic (Tr-J). The structure lies under the Tr-J unconformity.
Located near the center of the Casper Arch in central Wyoming and buried below the Late Triassic-Middle Jurassic (Tr-J) unconformity at a depth of ~1130 m, the 7-km-diameter Cloud Creek structure displays the morphological characteristics of a complex terrestrial impact crater. Geologic interpretation of the Cloud Creek structure is based on reflection seismic data, supplemented by gravity and magnetics mapping, and by data from ten exploratory wells that penetrated some part of the circular Cloud Creek structure. There is a 1.4-km-diameter central peak enclosed by a ring fault zone, and a 1.6 km-wide encircling skirt sloping into an annular trough that is overlain by a fault-bounded, partial rim anticline. Within the central peak, strongly deformed Paleozoic strata are centripitally uplifted ~520 m (Precambrian uplifted ~200 m) above extracrater levels and truncated by members of the Middle Jurassic Sundance Formation. Crater morphology has been modified by Early Jurassic erosion and an important Laramide overprint. The Cloud Creek impact event occurred near the lower end of the 40-m.y. time gap spanned by the Tr-J unconformity, i.e., near the close of Triassic (~190 +/- 30 Ma). (Stone)
A number of structural elements are visible to identify this complex crater, such as the central raised zone, the faulted rim with anticlinal horizon, and the ring-like trough [Stone and Therriault, 2003]. However, the relative coherent seismic events in the central peak of the Cloud Creek structure reveal a uniqueness. This uniqueness might be suggestive of the existence of the significant erosion, and that what we observe now are the remaining roots of the impact structure. In addition, the TR-J unconformity displayed on the borehole well logs and the severely fractured zone below the unconformity provide the evidence of erosion. Furthermore, based on the scaling relationship pointed out by Melosh [Melosh, 1989], for a crater which is 7 km wide, the central peak is supposed to be 700 m instead of the currently observed 520 m. This evident removal of estimated 200 m strata might be another hint of active erosion events during the deposit environments.(Wei Xie, 2014)
Planar deformation features (PDFs) in quartz have been identified and measured in samples collected from reported intervals 30 m and 330 m below the TR-J unconformity.
Brent Dalrymple, Radiometric Dating Does Work! Reports of the National Center for Science Education
Melosh, H. J. (1989), Impact cratering: A geologic process, Research supported by NASA. New York, Oxford University Press (Oxford Monographs on Geology and Geophysics, No. 11), 1989, 253 p., 1.
Stone, D. S. Geology of the Cloud Creek Impact Structure on the Casper Arch, Central Wyoming AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana
Stone, D. S., Therriault, A. M., The Cloud Creek structure, central Wyoming, U.S.A. – Impact origin confirmed, Meteoritics & Planetary Science, v.38, p.445-455. 2003.
Stone, D. S., Cloud Creek: A possible Impact Structure on the Casper Arch, Wyoming, The Mountain Geologist, vol. 36, No. 4, Rocky Mountain Association of Geologists. 2000.
Xie W. Seismic Characterization of A Possible Buried Impact Structure near Bow City in Southern Alberta Department of Physics University of Alberta