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The Late Triassic (Carnian-Norian) time interval is well represented by strata in the Wallowa and Baker terranes and in the Izee-Suplee area of central Oregon. Strata of the Olds Ferry terrane, by contrast, have received little attention beyond field mapping and reconnaissance-level efforts. This paper describes the sedimentology of Carnian-Norian deposits in the Olds Ferry terrane and describes a model for arc-flanking mixed carbonate-volcaniclastic sedimentation. A distinctive thin-bedded limestone unit in the lower Huntington Formation is underlain and overlain by volcanic and shallow intrusive rocks. Ammonite and bivalve age assignments indicate that the limestone unit spans the late Carnian to early Norian; portions of the section may, more specifically, represent the welleri or dilleri ammonite zones. Four lithofacies—Graded Skeletal Packstone and Mudstone, Tuffaceous Peloidal Grainstone, Skeletal Peloidal Packstone, and Lapilli-Tuff Breccia—record episodic sedimentation influenced by earthquakes, storms, and volcanic eruptions on an oxygen-poor carbonate slope apron. The limestone unit represents an echinoderm- and mollusk-dominated heterozoan faunal assemblage characterized by abundant delivery of unlithified carbonate sediment to deeper water.

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