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Date of Award
Master of Science (MS)
Suczek, Christopher A., 1942-2014
Engebretson, David C.
Babcock, R. Scott (Randall Scott)
The sedimentary rocks of the early to middle Eocene Blue Mountain unit compose the stratigraphic base of the otherwise predominantly basaltic Crescent Formation in the Olympic Peninsula, Washington. In the study area, primarily in northeastern portions of the Olympic Peninsula, the Blue Mountain unit consists of two distinct petrofacies, one a plagioclase-rich feldspathic arenite, the other a chert-rich lithic arenite. A third petrofacies is a feldspathic-lithic arenite and is a petrologic combination of the two distinct petrofacies. The source areas for the plagioclase-rich and chert-rich petrofacies are interpreted to be the Coast Plutonic Complex and San Juan Islands, respectively. The source area for the feldspathic-lithic arenite is interpreted to be a combination of the Coast Plutonic Complex and the San Juan Islands.
Limited sedimentologic data suggest that the Blue Mountain unit represents a submarine fan. Together, the Blue Mountain unit and basalt of the Crescent Formation compose the base of the Crescent terrane as exposed in the Olympic Peninsula. The Blue Mountain unit-basalt contact is depositional, and therefore the base of the Crescent terrane in this locality consists of continentally-derived sedimentary rocks. This relationship requires the basalt of the Crescent terrane to have originated near a continental landmass, probably North America. Furthermore, paleomagnetic data show that the Crescent terrane and the correlative Siletz terrane in Oregon have not undergone significant poleward displacement.
Relative plate motions indicate that the Kula and FaralIon plates were moving rapidly both poleward and perpendicular to the North American plate in the early Paleogene. Although uncertainties are large, the presence of interbedded continentally-derived sedimentary rocks, including the Blue Mountain unit, and the lack of poleward displacement suggest that the Crescent and Siletz terranes did not originate on the Kula or Farallon plates. Instead, the terranes probably formed inboard of the Kula-FaralIon-North American plate boundary, in sane type of marginal basin.
Crescent Formation, Paleomagnetism
Western Washington University
Subject – LCSH
Petrology--Washington (State)--Olympic Peninsula; Geology, Structural; Sedimentation and deposition--Washington (State)--Olympic Peninsula
Olympic Peninsula (Wash.)
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Einarsen, Jon M., "The Petrography and Tectonic Significance of the Blue Mountain Unit, Olympic Peninsula, Washington" (1987). WWU Graduate School Collection. 840.