JAMES RIVER STRUCTURE

JAMES RIVER STRUCTURE

by: Charles O’Dale

  • Type: Complex
  • Age Ma: <480 (Geological dating)a
  • Diameter: 5 km
  • Location: N 51° 54’47″ W 114° 55’ 11″

a The top of the anomaly structure was detected on top of the Cambrian units and the structure is estimated to form between the Late Cambrian and Middle Devonian time.

The red dot indicates the position of the James River structure, courtesy Breaking Science News at Sci-News.com Science Website.
The James River 5 km diameter structure is indicated by the red circle. (courtesy Google)
The James River structure from the south east approximately 4000 feet above ground level. “Ground zero” is image centre.
An interpreted horizon from the James River 3-D seismic survey shows many of the morphological characteristics of a complex impact crater. This view is of the Cambrian ‘event’ horizon as described by Isaac and Stewart (1993).(interpretation by Helen Isaac, visualization by Henry Bland)

Abstract

The James River impact structure in south-central Alberta is imaged on a 3-D seismic dataset. This structure is buried beneath 5 km of sediments and shows no surface or gravity expression. Also evidenced, is an annular synform and a central uplift.

The James River structure is located in southwestern Alberta and is consistent with complex crater morphology. The top of this structure is buried at a depth of nearly 4500 m and is truncated by an erosional unconformity marking the top of the Cambrian. This crater has a diameter of nearly 5 km, an annular moat, and a central uplift 2.4 km in diameter. Of exploration interest are structural traps formed by the terraces along the crater walls.

The recognition of the James River structure at ~4.5 km depth (Isaac and Stewart, 1993) indicates that at least some deeply located candidates are detectable. It is also likely that a significant number of structures have been observed but misidentified as being of non-impact origin.

Seismic data in the James River 3-D volume. Several interpreted horizons are shown. The upper horizon corresponds to the top of the Cambrian, the middle horizon corresponds to the Cambrian ‘event’, and the lower horizon corresponds to the Precambrian. Faulting in the James River data set is divided between shallow rim faults and deep central and rim faults.

The James River impact structure, located in the southeast Alberta plain, is a deeply buried circular structure with a rim-to-rim diameter of 4.8 km. The complex structural features observed on the 3D seismic data set, which included the raised central peak, annular synforms and rim faulted strata, have been well studied by Isaac and Stewart [1993]. Beneath the 4500 m thick strata, the top of the anomaly structure was detected on top of the Cambrian units and the structure is estimated to form between the Late Cambrian and Middle Devonian time. Figure 2.13 shows the synclinal features and a raised zone that performs the apparent erosion. However, due to the deep burial and lack of economic potential, no well has yet penetrated the target layer and as such there are no materials that could provide evidence of shock metamorphism. Thus, the impact essence of this potential impact structure is still waiting to be confirmed. (Wei Xie, 2014 )

2D seismic profile intercepted the James River structure, displaying almost symmetric synclines surround the eroded central peak. Image from Isaac and Stewart [1993].

The feature observed on the 3-D seismic data at James River is a cryptoexplosion structure, interpreted to be the result of a meteorite impact. It has a circular shape, raised circular central uplift, annular rim syncline and rim faults. The amount of central uplift is seen to decrease with depth and continuous reflections are seen within the uplift. The age of the deformed rocks is Cambrian and the structure was formed during Late Cambrian to Middle Devonian time. Although we do not have enough geological evidence to establish definitively the origin of the feature, we suggest that the morphology of the structure, the internal structure of the uplift and the decrease in uplift with depth strongly indicate an impact origin. (Isaac and Stewart, 1993)

References

Brent Dalrymple, Radiometric Dating Does Work! Reports of the National Center for Science Education

Isaac, J. H., and R. Stewart (1993), 3-D seismic expression of a cryptoexplosion structure, Can. J. Expl. Geophys, 29(2), 429-439.

M. J. Mazur, R. R. Stewart, and A. R. Hildebrand, Department of Geology and Geophysics, University of Calgary, SEISMIC CHARACTERIZATION OF BURIED POSSIBLE METEORITE IMPACT STRUCTURES. Lunar and Planetary Science XXX

M.J. Mazur, R.R. Stewart and A.R. Hildebrand, Department of Geology and Geophysics, THE SEISMIC SIGNATURE OF METEORITE IMPACT CRATERS University of Calgary, Calgary, Alberta, Canada

Xie W. Seismic Characterization of A Possible Buried Impact Structure near Bow City in Southern Alberta Department of Physics University of Alberta 2014