Cordilleran thrust belt-Rocky Mountain foreland interaction near Bannack, Montana
L. M. Johnson, J. W. Sears, 1988. "Cordilleran thrust belt-Rocky Mountain foreland interaction near Bannack, Montana", Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt, Christopher J. Schmidt, William J. Perry, Jr.
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Near Bannack, Montana, the Cordilleran thrust belt overlaps a Laramide Rocky Mountain foreland structure. The Precambrian-cored Armstead anticline formed along a steep, basement-rooted fault. Erosion breached the anticline, and Upper Cretaceous Beaverhead Group rocks, including distinctive conglomerates and tuffs, overlapped the truncated structure with angular unconformity. The Ermont thrust and associated structures then advanced into the area, disrupted the preexisting foreland structure, and tightly folded the Beaverhead Group.
The interaction between thrust structures and the Rocky Mountain foreland structure resulted in younger-over-older thrust faults and thrusts that cut down-section in the direction of transport.