Young's Thesis Abstract

Paleomagnetism of the Southern Crescent Formation, Olympic Peninsula, Washington

Megan Young

The mechanism of curvature for the Crescent Formation has been a subject of debate since the geology of the Olympic Peninsula was first studied. The Crescent Formation is an extraordinarily large swath of basalts that lies along the northern, eastern, and southeastern sides of the Olympic Peninsula. Although it is grouped as part of the Coast Range basalts, recent paleomagnetic studies of the northern part of the Crescent Formation suggest that it has a regional tectonic history distinct from other Coast Range basalts to the south. Previous attempts at paleomagnetic studies in the southern Crescent Formation have not yielded stable paleomagnetic directions. The majority of cores obtained for this study possessed stable magnetic directions, but scatter within each site is large. Comparison of the site mean directions with the expected middle Eocene pole for North America (82.8° north latitude, 170.4° east longitude) suggests that the sites have undergone some tilting and rotation, although the large directional scatter within each site prevents an accurate measurement of the amount of rotation and tilt. The inclinations and declinations obtained from the sites show different directions of rotation within a small area and also show inclinations inconsistent with any plausible model of regional deformation. These inconsistencies suggest that the areas sampled contain more structural complexities than simple bedding tilt, and that the site mean directions may reflect local, rather than regional, deformation and rotation.

University of Puget Sound