Portland State University. Department of Geology
Paul E. Hammond
Term of Graduation
Date of Publication
Master of Science (M.S.) in Geology
Volcanic ash -- Washington (State) -- Chumstick Formation, Stratigraphic geology -- Eocene
1 online resource (137 p.)
This study outlines the ash (tuff) bed stratigraphy (tephrostratigraphy) in the middle Eocene Chumstick Formation of central Washington. The tuff beds provide local marker beds enabling interpretation of the stratigraphy and structure of the formation. The chemical signature of these units provides the basis on which the units can be traced over broad areas in the basin of deposition. Correlations of tuff beds were obtained over distances of 41 km.
The tephrostratigraphy of the Chumstick Formation consists of nineteen tuff marker beds. Seventeen of these units are chemically characterized in this study. Ten elements were used to fingerprint these tuff beds. Of these elements, step-wise discriminant analysis shows Sc to be the most discriminatory followed in decreasing order of ability to discriminate by Eu, Fe, Hf, Yb, La, Ta, Sm, Th, and u. Those units which have a distinctive chemistry can be easily identified, and they can be recognized inspite of having under gone mild alteration or containing minor detrital admixture.
Cluster analysis suggests that the Chumstick tuffs are from at least two chemically different volcanic sources. One group is relatively enriched in rare earth elements compared with the other, and relative amounts of K and Eu strengthens this division.
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McClincy, Matthew John, "Tephrostratigraphy of the middle Eocene Chumstick Formation, Cascade Range, Douglas County, Washington" (1986). Dissertations and Theses. Paper 3633.