Graduate Thesis Or Dissertation
 

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  • The Pennsylvanian rocks in south-central Idaho and adjacent areas consist of three main facies: a platform facies
  • The Pennsylvanian rocks in south-central Idaho and adjacent areas consist of three main facies: a platform facies, a shelf facies, and a marginal basin facies. The platform facies is represented by the Amsden, Quadrant, and Tensleep Formations, in southwestern Montana and western Wyoming, and contain Middle and probably Lower Pennsylvanian strata. The shelf facies is represented by the Pennsylvanian part of the White Knob Limestone, which extends from the Lemhi Range to the White Knob Mountains west of the Lost River Range in south-central Idaho, and contains Lower, Middle, and Upper Pennsylvanian strata. The marginal basin facies is represented by clastics of the Middle and Upper Pennsylvanian part of the Wood River Formation, in the Wood River region in south-central Idaho, and the Lower, Middle, and Upper Pennsylvanian part of the Wells Formation in southeastern Idaho. Broad epeirogenic upwarps or eustatic sea level caused the shelf and platform to be alternately positive and negative during Pennsylvanian time. Pennsylvanian seas reached maximum inundation during Desmoinesian time after which a temporary offlap developed during Missourian through Middle Virgilian time on the platform and shelf areas, and epicontinental seas were restricted to the Wells and Wood River basins. During Late Virgilian time the seas spread to the east over former areas of post-Desmoinesian erosion on the shelf area Generalized isopachous and lithofacies maps of Pennsylvanian time-stratigraphic units are presented, with interpretations of the positions and periods of activity of positive and negative elements.
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