Stratigraphic variation and low-angle faulting in the North Hansel Mountains and Samaria Mountain, southern Idaho
Published:January 01, 1983
Richard W. Allmendinger, Lucian B. Piatt, 1983. "Stratigraphic variation and low-angle faulting in the North Hansel Mountains and Samaria Mountain, southern Idaho", Tectonic and Stratigraphic Studies in the Eastern Great Basin, David M. Miller, Victoria R. Todd, Keith A. Howard
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Sandstone and limestone of the Pennsylvanian and Lower Permian Oquirrh Formation in a gently dipping homocline on Samaria Mountain are about 850 m thick. In the North Hansel Mountains, several kilometers to the west and across a fault inferred to be a thrust, rocks of the same age range are four times thicker. The North Hansel section is deformed into open folds with wavelengths of a few kilometers, except where basal Oquirrh units are overturned eastward on a large scale near a low-angle fault between the Oquirrh and the Mississippian and Pennsylvanian Manning Canyon Shale. On the west side of Samaria Mountain, Oquirrh units are more tightly folded and overturned eastward in the upper plate of the Samaria Mountain thrust. This steep fault places older deformed parts of the Oquirrh on undeformed younger parts. We infer that the Samaria Mountain thrust is laterally continuous with the Manning Canyon detachment in the North Hansel Mountains.
The large change in thickness of the Oquirrh across the fault and the severe disharmonic deformation in upper and lower plates in both ranges suggest that initial movement on the fault was eastward-thrusting, probably during the Mesozoic. A structurally higher allochthon of Oquirrh limestones in the North Hansel Mountains crosscuts these older structures and may be Tertiary in age. Reactivation of the Samaria Mountain thrust and Manning Canyon detachment as a normal fault during the Tertiary is also possible.