Chapter 10: Structural features and emplacement of surficial gravity-slide sheets, northern Idaho-Wyoming thrust belt
Published:January 01, 1992
Steven E. Boyer, John R. Hossack, 1992. "Chapter 10: Structural features and emplacement of surficial gravity-slide sheets, northern Idaho-Wyoming thrust belt", Regional Geology of Eastern Idaho and Western Wyoming, Paul Karl Link, Mel A. Kuntz, Lucian B. Piatt
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Gravity-slide sheets are common in areas of sufficient topographic relief provided by extensional and compressional tectonism. They occur throughout the Basin and Range Province of Nevada and Utah but are perhaps best exposed in the thrust belt of southeast Idaho and northwest Wyoming. The Idaho-Wyoming slide sheets developed adjacent to extensional basin-bounding faults, which in turn were initiated at a ramp in the Absaroka thrust. Initial coherent sheets may have been up to 12 km2 in aerial extent, but as a result of differential movement rates, these larger sheets were broken into smaller blocks by strike-parallel extension during emplacement. Folds on the down-slope edges of the sheets suggest movement analogous to a tank tread: Through interbed shear the limestone beds rolled forward and were dragged beneath the leading edge of each sheet. It is not known whether initial emplacement was catastrophic or by creep, but undisrupted cleavages within footwall Tertiary mudstones and coherent bedding within the sheets suggest creep for at least the later phases of movement.