Taylor's Thesis Abstract

Paleomagnetism of the Crescent Formation Basalts, Olympic Mountains, Washington

Bryon Taylor

Correlation of Crescent basalt exposures is difficult due to the extensive deformation of the Crescent basalts on the Olympic Peninsula, Washington because of the active accretion of marine sediments along the western margin of the North American plate. As a result of the difficult nature of developing relative age correlation of different outcrops in the Crescent Formation, ten sites were sampled to develop a magnetostratigraphy through paleomagnetic analysis. Data extracted by this study are part of a larger regional project to develop a magnetostratigraphy and reversal sequence for the Crescent basalts. The data from this study show high site mean alpha 95 values which range from 27.13° to 180° and low k values ranging from 1.41 to 9.77. High alpha 95s and low k values indicate too much scatter in the data to obtain workable mean paleomagnetic directions for the sites. Of the ten sites, one site had weak initial intensities. While the other nine sites offered high initial intensities, rapid drops in intensities were observed in the alternating field demagnetization analysis. Thermal demagnetization analyses showed rapid drops in intensity at relatively low temperatures for all of the sites. The resulting data from the alternating field and thermal demagnetization analysis suggest that high initial intensities from nine of the ten sites are due to secondary magnetic overprints. Furthermore, studies by Nyberg (1998) and Normand (1998) reveal that scanning electron microscope analysis and reflected light microscopy analysis of similar outcrops to the west of this study area suggest alteration and secondary mineralization of the basalts. Because of the weak primary magnetic directions of the samples and the presence of magnetic overprints that could not be removed, the data is scattered and, as a result, is not useful for magnetostratigraphy.

University of Puget Sound