Graduate Thesis Or Dissertation

 

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4m90dz005

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Abstract
  • Approximately 23 square miles of the east-central part of the Tendoy Range are included in the thesis area which lies three miles west of Dell, Montana. Rocks ranging in age from Late Mississippian to Recent are exposed in the study area. The upper Paleozoic section includes approximately 4,200 feet (1,281 m.) of strata which are divided into four formations. The nine formations of Mesozoic aae total approximately 2,960 feet (903 m.) plus part of the Cretaceous-Tertiary Beaverhead Formation. Cenozoic strata in the thesis area include Beaverhead conglomerates, basaltic andesite flows, tuffs, and breccias, and unconsolidated gravels, alluvium, and alluvial fan gravels. The thesis area was examined in detail to define formation distribution and structural complications. The Triassic and Jurassic (Ellis Group) rocks were examined specifically in an effort to interpret their depositional environments. Sedimentary structures, fossils, and petrographic evidence indicate a shallow subtidal and intertidal setting for the deposition of Triassic rocks. Algal laminated strata within the Woodside Formation have not previously been described. Much of the Ellis Grout:, was deposited under shallow subtidal and locally shoaling conditions. Glauconite calcarenites in the Swift Formation may represent deposition in sand waves. Folding and faulting within the thesis area represent the overlapping influence of geosynclinal and cratonic tectonism in the hinge line setting of the Tendoy Range. The imposition of a southward-plunging anticline on a southwestward-plunging syncline has resulted in the overturning of the northern limb of the syncline. A low-angle thrust with eastward vergence has been developed in the Dry Canyon area. The thrust has been cut by a later high-angle reverse fault. White Knob strata (Mississippian) have been carried into the western margin of the thesis area on the Medicine Lodge thrust. The economic possibilities are not encouraging. The phosphate deposits of the thesis area have been analyzed and deemed uneconomical. Distance from intrusions precludes the chance of significant mineralization in the area. The petroleum potential for the area is doubtful. Late Cretaceous folding and erosion may have allowed escape of hydrocarbons from the potential source and reservoir rocks of the region. However, the Medicine Lodge thrust sheet may conceal structural and stratigraphic configurations capable of trapping oil and gas.
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