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Silicic Volcanism At The Northern And Western Extent Of The Columbia River Basalt Rhyolite Flare-Up: Rhyolites Of Buchanan Volcanic Complex And Dooley Mountain Volcanic Complex, Oregon, Adam M. Large
Dissertations and Theses
Two mid-Miocene (16.5-15 Ma) rhyolite volcanic centers in eastern Oregon, the Buchanan rhyolite complex and Dooley Mountain rhyolite complex, were investigated to characterize eruptive units through field and laboratory analysis. Results of petrographic and geochemical analysis add to field observations to differentiate and discriminate the eruptive units. Additionally, new geochemical data are used to correlate stratigraphically younger and older basalt and ash-flow tuff units with regional eruptive units to constrain the eruptive periods with modern Ar-Ar age dates.
Previous work at the Buchanan rhyolite complex was limited to regional mapping (Piper et al., 1939; Greene et al., 1972) and brief …
Post-Middle Miocene Geologic History Of The Tualatin Basin, Oregon With Hydrogeologic Implications, Doyle Coley Wilson
Post-Middle Miocene Geologic History Of The Tualatin Basin, Oregon With Hydrogeologic Implications, Doyle Coley Wilson
Dissertations and Theses
The geologic history and sedimentary till of the Tualatin Basin after Columbia River Basalt Group (CRBG) emplacement is assessed and related to groundwater characteristics. The 334 m deep HBD-1 core from the Hillsboro Airport, provides the primary information for sediment characterization and is supported by over 2400 well logs and cores, and four seismic lines. The sedimentary section above the 26 m thick paleosol on the CRBG in HBD-I is divided into two main groups: a 25 m thick section of Missoula flood sediments called the Willamette Silt overlies a 263 m thick finegrained sequence of fluvial Neogene sediments.
Pollen, …
Biostratigraphy Of The Cowlitz Formation In The Upper Nehalem River Basin, Northwest Oregon, Neil B. Shaw
Biostratigraphy Of The Cowlitz Formation In The Upper Nehalem River Basin, Northwest Oregon, Neil B. Shaw
Dissertations and Theses
Examination of stream and roadcut exposures of the Cowlitz Formation allows the selection of measured representative sections, and collection of fossils, from an area roughly defined by the intersection of the boundaries of Clatsop, Columbia, Tillamook and Washington counties in Oregon. The study defines the features of the local environment of deposition, correlates sections to derive a composite columnar section, and develops a checklist of species for both microfossils and megafossils of the Cowlitz Formation.