Graduate Thesis Or Dissertation
 

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3f462997j

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  • The oldest strata present in the Swales Mountain area are part of the Roberts Mountains allochthon. These include the western-facies Ordovician Vinini Formation and unnamed transitional-facies Devonian limestones. The Vinini Formation comprises dark cherts and black to brown shales deposited in a deep-water oceanic environment. The Devonian limestones include numerous lithologies: calcarenite, calcisiltite and calcilutite in thin-bedded turbidite sequences, dacryoconarid-bioclastic calcarenite and calcisiltite, crystalline limestone, laminated quartz-silty dolomite, and pebbly lime mudstone. These rocks were deposited in an outer shelf or slope environment. The autochthonous Paleozoic sequence consists of Antler limestone turbidites of the redefined Kinderhookian Camp Creek sequence. The lower unit of the Camp Creek sequence is characterized by black hemipelagic carbonate mudstones with sparse thin sandy limestone interbeds; conodonts from the lower unit indicate an age somewhere within the spans of the sandbergi to isosticha-Upper crenulata Zones. The upper unit consists primarily of easterly derived quartz-sandy limestone turbidites, which were deposited during isosticha-Upper crenulata Zone time. These rocks were deposited at bathyal depths in the Antler foreland basin ("flysch trough"), which was actively subsiding through much of Early Mississippian time. The Roberts Mountains allochthon at Swales Mountain consists of the Ordovician western facies rocks with Devonian transitional facies rocks at its base and in imbricate thrust slices. The allochthon was obducted onto continental crust during late Kinderhookian and early Osagean time; as it progressed over the foreland, Devonian outer shelf and slope strata were incorporated in its basal parts. The allochthon moved into the map area by the end of isosticha-Upper crenulata Zone time, cutting up through the strata of the Camp Creek sequence.
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