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The AAPG/Datapages Combined Publications Database

Wyoming Geological Association

Abstract


The Cretaceous Geology of Wyoming; 36th Annual Field Conference Guidebook, 1985
Pages 59-65

Stress Analysis of the Casper Mountain — Emigrant Gap Anticline Juncture, Natrona County, Wyoming

William C. Beck, Arthur E. Burford

Abstract

Casper Mountain and Emigrant Gap Anticline lie at the southwest side of the Powder River Basin and abut at their west and southeast ends, respectively. Deformation associated with the anticline was the result of at least two stress fields; each had the axis of maximum compressive stress (sigma 1) oriented northeast-southwest and horizontally. Comparison of equal-area, lower hemisphere projections of poles to joints before and after bedding rotation to horizontal shows markedly more distinct groupings of maxima after rotation and suggests the following sequence of stress fields. The initial sigma 1/sigma 3 stress plane was horizontal, followed by a vertical sigma 1/sigma 3 stress plane. Dominant folding occurred while the latter stress field was active. Return to the initial stress orientation is suggested by Previous HitstrikeNext Hit-slip faults that offset folded strata.

Deformation of Casper Mountain was also the result of at least two stress fields as indicated by equal area projections; each had the axis of maximum compressive stress oriented approximately north-south, horizontal. Similar to that of Emigrant Gap Anticline, the initial sigma 1/sigma 3 stress plane was horizontal, followed by a vertical sigma 1/sigma 3 stress plane. Dominant folding and thrusting occurred while the latter stress field was active. Return to the original stress orientation is suggested by Previous HitstrikeTop-slip faults that offset thrusts and folded strata. Relations of structural features including cross-cutting of Emigrant Gap Anticline by the Casper Mountain fold axis and faulting, the bending of the western part of the axis of Casper Mountain, and the presence of cross folds on Emigrant Gap Anticline indicate that Casper Mountain has been thrust over Emigrant Gap Anticline.


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