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Evaluation of Fractures on Monkshood Anticline, a Detachment Fold in the
William R. Jamison2
Monkshood anticline is a well-exposed surface
anticline located in the Foothills in northeastern British Columbia. Extension
fractures are well developed in the Prophet Formation (a carbonate-shale-chert
sequence) throughout this fold. Virtually all of these fractures are filled
with some combination of calcite and quartz cements. The fractures formed
and the mineral cements were deposited during the fold development.
Most fractures on Monkshood anticline have
formed at high angles to bedding, and they commonly fall into two to three
distinct orientation sets. The dominant fracture trend is aligned with
the fold axis through the backlimb of the fold, but there is considerable
variance in the dominant orientation in the forelimb. An order of magnitude
variation is found in fracture densities across this fold, and over two
orders of magnitude variation occur in mean fracture aperture. These variations
in density and aperture do not correlate with particular structural positions.
Fracture trace lengths exhibit power-law distribution patterns, suggesting
fractal character. Fracture aperture displays a roughly linear correlation
to volumetric fracture strain, but shows no consistent association with
either density or trace length.
1997. The American Association of Petroleum Geologists. All rights reserved.
received January 5, 1996; revised manuscript received August 19, 1996;
final acceptance January 20, 1997.
for Earth Resources Research, Department of Earth Sciences, Memorial University
of Newfoundland, St. John's, Newfoundland A1B 3X5, Canada. Present address:
The Upper Crust, Inc., 7340-11th Street SW, Calgary, Alberta T2V 1N1, Canada.
study has been made possible through the financial support of Amoco Canada
Petroleum Ltd., Mobil Oil Canada, Phillips Petroleum Resources Ltd., Talisman
Energy Ltd., and a National Science and Engineering Research Council (NSERC)
grant. Stable isotope analyses were conducted by Mark Wilson. Stochastic
modeling was conducted using the program FracMan®,
vended by Golder Associates, Inc. This manuscript greatly benefited from
the thoughtful and constructive reviews of Stephen Laubach, John Lorenz,
and Ron Nelson.
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