Late Paleozoic formations of central Oregon

Abstract

Fifteen miles southeast of Paulina, central Oregon, unaltered Carboniferous and Permian rocks yield much information regarding late Paleozoic history of this region. Three formations are described as follows: (1) the Coffee Creek (Lower Carboniferous) marine limestones and sandstones bearing Gigantella, Striatifera , and Dibunophyllum ; (2) the Spotted Ridge (Pennsylvanian) disconformably above the Coffee Creek, consisting of cherts, sandstones, heavy conglomerates, and mudstones, in part land-laid, yielding a well-preserved flora provisionally assigned to Pottsville; (3) Coyote Butte (Permian) limestones and sandstones with a large fusulinid, coral, and brachiopod fauna, resting unconformably on both the Spotted Ridge and Coffee Creek. The faunas indicate a closer relationship with northern California, Alaska, and the Old World than with other known areas in North America. Asiatic affinity of the Coyote Butte Permian fauna is particularly strong. The Paleozoic beds were folded after deposition of the Coyote Butte Permian and before accumulation of the Triassic conglomerates and sands. The Triassic and older strata suffered further compression later. Strikes of folds within the steeply dipping Paleozoics locally depart widely from trends in superjacent Triassic beds. Abundant coarse sandstone in all formations and heavy conglomerates in the Spotted Ridge Pennsylvanian bespeak high near-by terrain during much of late Paleozoic and conform to structural evidences of diastrophism.