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Date Permissions Signed
Date of Award
Master of Science (MS)
Housen, Bernard Arthur
Suczek, Christopher A., 1942-2014
DeBari, Susan M., 1962-
Burmester, Russell F.
The Spieden Group in the San Juan Islands of Washington State consists of the Lower Cretaceous Sentinel Island Formation and the Upper Jurassic Spieden Bluff Formation. In order to constrain the location of its origin, paleomagnetism of the sedimentary rocks of the Spieden Group was studied to obtain paleolatitudes. Two components of magnetization were measured in most of the Sentinel Island Formation specimens. The second-removed component had a mean in-situ direction of D = 34.1°, I == 44. 2°, α95 = 12.0° and a mean tilt-corrected direction of D = 49.3°, I = 71.5°, α95 = 6.9°. Uncertainty that some of the scatter of directions was due to fault block rotation not corrected for during unfolding suggests inclination-only analysis may be appropriate; it yielded a tiltcorrected inclination of I = 64.0°, α95 = 7.9°. Three components of magnetization were extracted from most of the Spieden Bluff Formation specimens. The third-removed component had a mean in-situ direction of D = 82.5°, I = 82.0°, α95 = 23.0° and a mean tilt-corrected direction of D = 78.3°, I = 71.3°, α95 = 16.9°. Segregating directions according to how much a component contributed to the total remanence isolated characteristic components that were unfolded incrementally. The best clustered direction was from components that constituted 70-80% of NRM intensity and yielded a magnetic direction of D = 48.2°, I = 65.0°, α95 = 20.9°. The Cretaceous still-stand pole was used as a reference pole for the Cretaceous Sentinel Island Formation. The expected paleomagnetic direction calculated for the present position of the Sentinel Island Formation of D = 334.6°, I - 74.0° corresponds to a latitude of 60° N. This latitude contrasts with the paleolatitude best estimate of origin for the Sentinel Island Formation (derived from its 64° inclination) of 45.7° N latitude. The pole of the Brushy Basin Member of the Morrison Formation was used as a reference pole for the Jurassic Spieden Bluff Formation. The expected paleomagnetic direction calculated for the Jurassic Spieden Bluff Formation of D = 327.4°, I = 65.3° corresponds to a latitude of 47° N, which is identical to the paleolatitude for the Spieden Bluff Formation derived from its 65° inclination.
Paleomagnetism, Sedimentary rocks, Spieden Group
Western Washington University
Subject – LCSH
Paleogeography--Washington (State)--San Juan Islands
San Juan Islands (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.
Dean, Patricia Allison, "Paleogeography of the Spieden Group, San Juan Islands, Washington" (2002). WWU Graduate School Collection. 823.