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AAPG Bulletin


Quantitative Evaluation of Fractures on Monkshood Anticline, a Detachment Fold in the Foothills of 
Western Canada

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.

©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.

1Manuscript received January 5, 1996; revised manuscript received August 19, 1996; final acceptance January 20, 1997.

2Centre 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.

This 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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