Abstract

The Fencemaker allochthon, a regionally extensive tectonic feature at the outer edge of the Mesozoic North American foreland, contains Upper Triassic flysch deposited in a deep-water basin that occupied much the same geographic tract as does the present allochthon. Polyphase deformation in the allochthon has been sequentially removed to determine the pre-tectonic position of strata. Rocks of the allochthon in the East Range of north-central Nevada include calcareous and siliciclastic strata transported by varied sub-aqueous processes. Thirteen facies are recognized in the allochthon. Vertical facies sequences are indicative of deposition on middle and inner portions of a submarine fan during retrogradational and progradational cycles. Flysch deposition began in the early Norian and continued through the middle Norian with northward migration of major siliciclastic conduits. Penecontemporaneous shelf strata compose the autochthon to the Fencemaker thrust, the eastern margin of the bivergent Fencemaker allochthon, and record early Norian deltaic and middle Norian post-deltaic shelf sedimentation. The Fencemaker thrust was localized by the shelf-to-basin transition. Sediments in both the allochthon and the autochthon were derived primarily from the Triassic craton far to the east with addition from local sites. Regional Mesozoic unroofing in north-central Nevada probably occurred after Late Triassic time.

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