Abstract

A thrust system at least 40 km long and with as much as 2,000 m of shortening has been mapped in the southern High Plateaus of Utah, partly within Bryce Canyon National Park. Seismic data clearly reveal that the thrusts are of thin-skinned, ramp-flat style, soling out in evaporite-rich layers of the Jurassic Carmel Formation. Mapping discloses that large portions of the thrusts terminate upward in fault-propagated folds, marked by vertical to overturned beds. Spaced cleavage reveals that some shortening is accommodated by pressure dissolution. Shallow drilling for coal provides data suggestive of more than one episode of thrusting. An older event predates deposition of the Upper Cretaceous and Paleocene(?) Canaan Peak Formation. This deformation is presumably related, in the broadest sense of the term, to the Sevier orogeny. The younger thrusting is southvergent and involves rocks as young as the lower to middle Eocene, white limestone member of the Claron Formation, a formation that is considered post-orogenic by most geologists. The upper age of the younger event is not constrained in time, and its tectonic significance remains poorly understood.

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