Portland State University. Department of Geology.
Marvin H. Beeson
Date of Publication
Master of Science (M.S.) in Geology
Geochemistry -- Oregon -- Portland Metropolitan Area, Lava -- Oregon -- Portland Metropolitan Area, Sediments (Geology) -- Oregon -- Portland Metropolitan Area
1 online resource (3, ix, 182 p.)
Instrumental Neutron Activation Analysis (INAA) was used to identify geochemical groups in Boring Lava along the west side of the Tualatin Mountains, and in sediments of the Portland and Tualatin basins. Samples of Boring Lava were obtained from TriMet drill core collected during planning of the tunnel alignment for the Westside Light Rail line. Additional samples of Boring Lava were collected from outcrops along the west side of the Tualatin Mountains. Samples of sediment from the Tualatin and Portland basins were obtained from drill core collected during an Oregon Department of Geology and Mineral Industries (DOGAMI) Earthquake Hazards Mapping project. INAA of Boring Lava samples resulted in the identification of three geochemical groups. Additional data sets, including x-ray fluorescence geochemistry, magnetic polarity, and age dates, allowed for the distinction of three Boring Lava units. The Boring Lava of Barnes Road is a young, normal unit, the Boring Lava of Sylvan Hill is an older normal unit, and the Boring Lava of Cornell Mountain is the oldest, reversed unit. The surf ace distribution, identified using topography and outcrop geochemistry, is consistent with the subsurface distribution, identified using boring logs and core geochemistry. Volcanic vent locations are proposed at topographic highs within the identified surface distribution of the Boring Lava of Barnes Road. INAA of sediment samples resulted in the identification of seven groups: (1) Columbia River source sediments, (2) lower Troutdale Formation, (3) Reed Island ashes, (4) young Columbia River sediments, (5) highalumina basalt sediments, (6) episodic Cascadian volcanic sediments, and (7) Columbia River Basalt Group (CRBG) sediments. Only the CRBG sediments group was identified in the Tualatin basin, while all seven groups were identified in the Portland basin. This appears to demonstrate that the sediment packages in the two basins are different. Finally, each sediment group can be placed into one of three broad geochemical categories: Columbia River source sediments and lower Troutdale Formation represent a Columbia River or continental source; Reed Island ashes, young Columbia River sediments, high-alumina basalt sediments, and episodic Cascadian volcanic sediments represent a Cascadian or local source; and CRBG sediments represent residual soils or sediments overlying Columbia River basalt flows.
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Barnes, Michelle Lynn, "Geochemistry of the Boring Lava along the West Side of the Tualatin Mountains and of Sediments from Drill Holes in the Portland and Tualatin Basins, Portland, Oregon" (1995). Dissertations and Theses. Paper 4990.