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Book Chapter

Natural Fractures in Folded Sandstones of the Tensleep Formation, Wyoming

By
John C. Lorenz
John C. Lorenz
FractureStudies LLC 99 Rainbow Rd. Edgewood, New Mexico, 87015, U.S.A. (e-mails: john@fracturestudies.com, scott@fracturestudies.com)
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Scott P. Cooper
Scott P. Cooper
FractureStudies LLC 99 Rainbow Rd. Edgewood, New Mexico, 87015, U.S.A. (e-mails: john@fracturestudies.com, scott@fracturestudies.com)
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Published:
January 01, 2013

Abstract

Several types of meter-scale structures accommodated strain during folding of the Tensleep sandstones at Flat Top Anticline, a compound fold overlying an east-northeast to west-southwest striking Laramide thrust fault in southeastern Wyoming. The suite of structures includes (1) syn-depositional hydraulic injection fractures that were reactivated in shear and extension during folding, (2) early-formed hinge-oblique extension fractures, (3) later-formed hinge-parallel extension fractures concentrated on the crest and forelimb, (4) scattered small shear planes oriented both parallel and oblique to the large-scale eolian cross-bed foresets, (5) larger-scale bedding-parallel shear between sedimentary units on the steeper forelimbs, (6) faults, and (7) rare scattered deformation bands. The hinge-oblique extension fractures strike parallel to the direction thrusting, which was not normal to the basement fault. Most of these structures formed due to extension of he strata parallel and oblique to the anticlinal hinge folding developed over the thrust fault. The degree and type of extension fracturing vary by structural position: hinge-oblique fractures dominate the unfolded backlimb, whereas both hinge-oblique and hinge-parallel fractures developed on the forelimb and anticlinal crest. Paradoxically, extension fracturing is minimal where folding is most acute at the westernmost Pine Butte substructure, where small faults, bedding-parallel shear, and reactivation of the preexisting, well-developed suite of hydraulic injectites accommodated most of the strain. Many of these structures record more than one structural event.

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AAPG Studies in Geology

Application of Structural Methods to Rocky Mountain Hydrocarbon Exploration and Development

Constance N. Knight
Constance N. Knight
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Jerome J. Cuzella
Jerome J. Cuzella
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Leland D. Cress
Leland D. Cress
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American Association of Petroleum Geologists
Volume
65
ISBN electronic:
9781629812632
Publication date:
January 01, 2013

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