Graduate Thesis Or Dissertation
 

Geology of part of the southeastern Wallowa Mountains, northeastern Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/td96k6092

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  • Within 40 square miles of the southeastern Wallowa Mountains, Oregon, eugeosynclinal Permian and Triassic formations comprising a section about 25,000 feet thick have been exposed by uplift and erosion of overlying Miocene Columbia River basalt. Deposition appears to have been continuous from Permian into Upper Triassic, but an apparent angular nonconformity exists between Triassic formations. Neritic clastics of the Permian Trinity Creek formation are overlain by mixed volcanics and elastics of the Triassic Imnaha formation, which is terrestrial and littoral in its lower Russel member and neritic in Its upper Norway member. Sandstone and conglomerate of the Upper Triassic Lower Sedimentary Series apparently rest unconformably on deformed pillow lavas and breccias of the Norway member. A varied suite of small stocks Intrudes the area. Gabbroic units of the Fish Lake complex are most widespread; other stocks are composed of metadiorite, keratophyre, bostonite, and trondjemlte. Varied dikes are extremely abundant In older formations. Marble and skarn of uncertain age, but believed unrelated to the Imnaha or Trinity Creek formations, are intimately associated with gabbroic stocks. Deformation increases from east to west, and culminates with an overturned anticline in the Upper Triassic Lower sedimentary Series at the western margin of the area. Faulting is minor except for the Pine Creek reverse fault which has a minimum vertical displacement of 2500 feet. Alpine topography resulted from Pleistocene stream erosion and glaciation; post-Pleistocene erosion has not been extensive.
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