DEEP BAY FLAT-FLOORED CRATER

Type: Flat floor
Age ma: 99 ± 4^a – CRETACEOUS
Diameter: 9.5^b km
Depth: 220m
Location: N 56° 24’ W 102° 59’
Shock Metamorphism: PDF in quartz grains and feldspar.
Dating Method: Stratigraphy – Cretaceous sediments

^a Undisturbed Mesozoic strata near the centre of the bay, along with fossil evidence, have been used to estimate the age (Innes et al., 1964 ; Grieve and Robertson, 1979). Fossil evidence indicates 95 to 102 Ma (Sweet, 1999)

^b Based on diameter of residual gravity anomaly (Dence 2004).

Saskatchewan, Canada – Gow Lake and Deep Bay craters,Carswell, Dumas, Elbow, Maple Creek and Viewfield impact structures. Yellow = ATHABASCA FORMATION, Pink = PRECAMBRIAN BASEMENT COMPLEX, Grey = INTERIOR PLAINS. Courtesy Breaking Science News at Sci-News.com Science Website.

The unique topographical features of Deep Bay are well brought out in this map of the southern end of Reindeer Lake that shows the almost perfect circularity of Deep Bay and the absence of islands within in it, Innes et al (1964)

Deep Bay Impact Crater looking south-east from GOZooM (Reindeer Lake in the foreground).

Deep Bay Structure Introduction

General Area: Low hills in the Canadian Shield. The area is forested and has been glaciated. The target rocks are crystalline.

Specific Features: Structure is a circular feature 11 km in diameter, at the south end of Reindeer Lake. The crater is defined by a 220 m deep circular bay in a lake which elsewhere averages only -50 m in depth. The shape and depth of the bay contrast sharply with other lakes in the area. Local Indian legend has a taboo on fishing in the bay, presumably due to its unusual appearance and depth. A subtle rim -100 m high surrounds the bay at a diameter of 13 km. Additionally, a faint fracture halo has been mapped from aerial photographs and SIRB (shuttle imaging radar B) imagery.

The Deep Bay flat floored crater is a nearly circular lake near the south end of Reindeer Lake. Partially surrounding the bay is a ridge up to 100 m above the lake with a maximum diameter of 13 km, which probably represents the outer rim of the crater.

Topographic, geological and geophysical evidence suggest that the structure of Deep Bay in Saskatchewan is the result of the explosion of a meteorite.

Deep Bay Crater – Saskatchewan (Courtesy NASA).

Deep Bay Crater – Saskatchewan (Google image).

The red dot represents the approximate area of the Deep Bay impact 99 million years ago in the Cretaceous Period.

The underground structure of the buried crater was studied by a refraction seismic survey and was found to be 2,000ft. deep and six miles in diameter. The crater appears to be filled with relatively soft sediments, possibly Mesozoic shales. Seismic velocities of 15,000 ft./sec. were measured, within the Precambrian rocks under the crater and in its vicinity against a velocity of 20,000 ft./sec. at greater distances from the structure.

The low velocity of propagation of seismic waves within these rocks must be due to fractures resulting from the explosion of the meteorite. The zone in which the Precambrian rocks are fractured was found to extend for three miles beyond the crater and to great depth under the structure.

A ground magnetometer survey permitted an independent estimate of the depth of the Precambrian rocks under the central portion of Deep Bay and correlates well with the seismic results. Both geophysical methods reveal a structure which conforms closely to the shape of a meteorite crater (Sander et al, 1964).

Drilling by the Dominion Observatory in the early 1960s into the structure revealed shocked and fractured metamorphic rocks flanked by mixed breccia deposits. PDF in quartz grains and feldspar were recovered from the drill site DOM 66-1 (see bathymetric diagram) (Dence et al., 1968). This is geologic confirmation of a cosmic impact.

Topography and bathymetry of Deep Bay. Also indicated are location of drill holes and a geologic cross-section based on these drill holes (bottom). Innes et al (1964). PDF in quartz grains and feldspar were recovered from the drill site DOM 66-1 (Dence et al 1968).

Seismic and Magnetic Investigation of the Deep Bay Crater. Sander 1964

Several mechanisms related to impacts may radically change the magnetic properties of target rocks. Peak pressures in autochthonous rocks may reach ~30 GPa at impact, which is sufficient to produce shock demagnetization and remagnetization effects.

At Deep Bay diamond drilling near its center has confirmed that Cretaceous sedimentary rock lies within the crater, indicating a minimum crater age of 140 million years. Analysis of deformed rock and gneiss breccia encountered in a drill hole one mile from shore suggests that the original crater diameter is about 31,000 feet, considerably less that first estimated (Innes 1964).

These aerial images under a clear blue sky were taken from GO ZooM on our trip to the west coast in 2012. At the time we took these images, the Saskatchewan prairies 100 km to the south were experiencing severe thunderstorms and tornadoes!!

Deep Bay Crater north east shore. Target rocks along this shoreline are intensely fractured. This fracture halo extends out to ~19 km.

At Deep Bay the circular fracture zone marks approximately the outer limit of the fractured zone and may be interpreted as a hinge line about which the granitic rocks forming the rim have been uplifted. Indeed the rocks within this circle, have the general appearance of having been uplifted and shattered into huge blocks without having undergone much horizontal movement. (Innes et al 1964).

The Deep Bay structure is a circular feature 11 km in diameter, at the south end of Reindeer Lake. The crater is defined by a 220 m deep circular bay in a lake which elsewhere averages only -50 m in depth. The shape and depth of the bay contrast sharply with other lakes in the area. Local Indian legend has a taboo on fishing in the bay, presumably due to its unusual appearance and depth. A subtle rim -100 m high surrounds the bay at a diameter of 13 km. Additionally, a faint fracture halo has been mapped from aerial photographs and SIRB radar imagery.

Low hills in the Canadian Shield. The area is forested and has been glaciated. The target rocks are crystalline.

Images illustrating the eastern shore of the Deep Bay crater.

Side Note

Relative sizes of Holleford, Brent and Deep Bay Impact Craters.

References

[see – METEORITE]

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

Dence, Michael R. Structural evidence from shock metamorphism in simple and complex impact craters: Linking observations to theory. Meteoritics & Planetary Science 39. Nr 2, 267-286 (2004).

Dence, M. R., Innes, M.J.S. and Robertson,P.B., Recent geological and geophysical studies of Canadian craters. in Shock Metamorphism of Natural Materials, eds. B. M. French and N. M. Short, Mono Book Corp., Baltimore, MD, pp. 339-362. 1968.

Grieve R.A.F., Impact structures in Canada, Geological Association of Canada, 2006.

Grieve, R. A. F., Robertson, P. B., The terrestrial cratering record. 1. Current status of observations. Icarus, v. 38, pp. 212-229. 1979.

Innes, M.J.S., 1964, Recent advances in meteorite crater research at the Dominion Observatory, Ottawa, Canada: Meteoritics, v.2, n.3, p. 219-241

Sander, G. W., Overton, A. and Bataille,R., Seismic and magnetic investigation of the Deep Bay crater. Ottawa Dominion Observatory Contributions, v. 5, 15 p. 1964.

Sweet, A. R., Applied research report on 4 mid Cretaceous samples from boreholes in the Deep Bay crater, Northern Saskatshewan, Paleontological Report, Department of Natural Resources Canada 3-ARS-1999. 1999.

Earth Impact Database