Cypress Hills region - Bedrock Geology and
Astroblemes around the Cypress Hills
Astroblemes are roughly circular impact structures, thought
to be formed by meteor impact. If the impacts occurred in the
the craters may have a distinct surface expression, as at the
Meteorite Impact Crater in Ontario (see MacLennan 1988). However,
when impacts occurred in the distant geologic past, astroblemes
be deeply buried and only detectable through geophysical methods
The Eagle Butte astrobleme, at the west end of the Cypress Hills,
appears on the latest edition of the Geology of Alberta
map (1999). This map shows two astroblemes in Alberta; the second
River) is in the far north of Alberta. However, the latest GSC
Geology map of the area (Okulitch et al. 1996) shows three
astroblemes around the margin of the Cypress Hills: Eagle
Butte, Maple Creek (which is actually south of Piapot),
and Govenlock (south of the town of the same name and
immediately north of the US border). In their note accompanying
the map, their comments on these are as follows:
Three sub-circular structures within the Bearpaw and
older formations north, west and south of the Cypress
Hills are herein interpreted as astroblemes. The enigmatic
Maple Creek structure is of mid-Maastrichtian age; the
others are of the same age or younger. The Eagle Butte
structure has been verified as an astrobleme, but the
Govenlock structure remains to be studied. The three
may have formed during impact of a cluster of meteorites
that perhaps contributed to faunal declines preceding
extinctions at the end of the Cretaceous.
For Eagle Butte, Westbroek (1997) says the following:
The Eagle Butte impact crater is located in southeastern
Alberta. It is a complex crater about 18 km in diameter
with structural uplift at its core of some 250-300 m
(Sawatzky 1976). Its impact origin has been proved by
the discovery of shatter cones at the surface
(Lawton et al. 1993; Hodge 1994). An area of active
hydrocarbon exploration, it has been extensively covered
by seismic acquisition lines and the structure has been
drilled in a number of localities. To date, a few gas
accumulations have been found associated with the structure. (p.
Robertson and Grieve (1975) list Eagle Butte as a "probable"
impact crater, together with one at Elbow, Saskatchewan.
However, this was written in 1975
and more work has been done since then. Ezeji-Okoye (1985)
describes the Eagle Butte feature in more detail.
A recently-published compendium by Grieve (2006) summarizes the
publicly-available data for the Eagle Butte structure. He
comments on several occasions that subsurface and geophysical
data are proprietary and not readily available. Grieve (2006: 72)
notes deformation in the Lower and Upper Cretaceous formations,
between the Alberta Shale and Bearpaw formations, with
disturbance extending to at least 1.3 km depth. He suggests that
the timing of the event is younger than Upper Cretaceous (because
bedrock units of this age are disturbed) but notes that the age
is not well-constrained. Hanova et al. (2005) provide
visualizations of the north-east quadrant of the structure, based
on well and seismic data. Their analysis shows multiple faults
and curved fault planes. Although these do delineate a roughly
circular feature, they note that the structure is complex and
detected a "rose-petal structure, as opposed to simply only
The impact structure is not well-expressed at the surface, and
is not obvious in the field. Presumably, glaciation and
subsequent geomorphic processes would have removed any marked
crater, if one had been present prior to glaciation. However,
satellite imagery (see below) does show a roughly
circular feature, marked especially in the stream network and
You can view an image of Eagle Butte here.
The Whitecourt Impact Crater in northwest Alberta provides a
comparative example. This small crater is estimated to have been
formed in the late Holocene and has a more obvious surface
expression (Herd et al. 2008; Kofman et al. 2010).
You can view an image of the Whitecourt Crater here.
Finally, a useful article by Donofrio (1998) has some helpful
maps showing the distribution of astroblemes in Canada, although
it does not mention Eagle Butte or the newly-identified
- Donofrio, R. R. 1998
- North American Impact Structures Hold Giant Field Potential.
Oil & Gas Journal (May 11, 1998):69-83.
Available in PDF form at http://www.edge.o
- Ezeji-Okoye, S. 1985
The Origin of the Eagle Butte Structure. PanCanadian
Petroleum Limited, unpublished report 75 pages.
- Grieve, R. A. F. 2006
Impact Structures in Canada. GEOtext No. 5. Geological
Association of Canada, St John's, Newfoundland, Canada. x + 210
Provides a useful summary of twenty-eight
impact structures in Canada, including maps, subsurface data,
geophysical data, and detailed citations. The text includes
discussion of the Eagle Butte (pp. 71-73) and Maple Creek (pp.
113-114) structures as well as several others that occur in the
Prairie Provinces. The Whitecourt Meteorite Impact Crater,
is too recent to be included. (02/Sep/2010).
- Hanova, J., D. C. Lawton, J. Visser, A. R.
Hildebrand, and L. Ferriere 2005
- 3D Structural Interpretation of the Eagle Butte Impact
Structure, Alberta, Canada.
. 36th Annual Lunar and Planetary Science Conference, March
2005, in League City, Texas, Abstract no. 2355 2 pages.
On-line document available at htt
- Herd, C. D. K., D. G. Froese, E. L. Walton,
R. S. Kofman, E. P. K. Herd, and M. J. M. Duke 2008
- Anatomy of a young impact event in central Alberta, Canada:
Prospects for the missing Holocene impact record.
AEU SCI QE 1 G3455 DOI: 10.1130/G25236A
- Hodge, P. 1994
Meteorite Craters and Impact Structures of the Earth.
Cambridge University Press, Cambridge, England, UK. 124
- Kofman, R. S., C. D. K. Herd, and D. G.
- The Whitecourt meteorite impact crater, Alberta, Canada.
Meteoritics and Planetary Science 45(9):1429-1445.
- Lawton, D. C., R. R. Stewart, and R. Gault
- The Geophysical Expression of the Eagle Butte Impact
. Paper presented at the 19th Annual Meeting of the Canadian
Geophysical Union, Banff, Alberta.
- MacLennan, M. J. 1988
- The Holleford Meteorite Impact Crater.
The Canadian Geographer 32(2):173-177. Canadian Landform
Examples - 8, vol. 32.
This crater is located near Kingston,
This provides a useful description of a crater that is still
clearly visible at the ground surface.
- Okulitch A. V., D. A. Lopez, and T. Jerzykiewicz
Geology, Lethbridge, Alberta-Saskatchewan, Montana.
Geological Survey of Canada, Map NM - 12 - G, scale 1:1,000,000.
National Earth Science Series, Geological Atlas. Geological
of Canada, Ottawa, Ontario, Canada.
Consists of four map sheets.
- Robertson, P. B., and R. A. F. Grieve 1975
- Impact Structures in Canada: Their Recognition and
Journal of the Royal Astronomical Society of Canada 69:1-
This is available on-line (PDF format)
the Royal Astronomical Society of Canada website at http://www.rasc.ca/journal/
- Sawatzky, H. B. 1976
- Two Probable Late Cretaceous Astroblemes in Western Canada
Eagle Butte, Alberta and Dumas, Saskatchewan.
- Westbroek, H. 1997
Seismic Interpretation of Two Possible Meteorite Impact
Craters: White Valley, Saskatchewan and Purple Springs,
Alberta. Unpublished M.Sc. dissertation. Department of
and Geophysics, Calgary, Alberta, Canada. 145 pages.
Available on-line at http://www.cr