Physical Sciences and Mathematics Commons^™

An Analysis Of Gravity Surveys In The Portland Basin, Oregon, Janice C. Perttu

Dissertations and Theses

The geologic setting of the Portland Basin is ideal for gravity surveys because of the large density contrasts between geologic units. The Portland Basin consists of a north-northwest-trending syncline in the Columbia River basalt overlain by Pliocene to Recent alluvium. This study was undertaken to define structures in the Portland Basin which are obscured by the alluvium.

An areal gravity survey of the Portland Basin covering approximately 450 square kilometers was conducted for this study.

Geophysical And Geochemical Analyses Of Selected Miocene Coastal Basalt Features, Clatsop County, Oregon, Virginia Josette Pfaff

Dissertations and Theses

The proximity of Miocene Columbia River basalts to the "locally-erupted" coastal Miocene basalts in northwestern Oregon, and the compelling similarities between the two groups, suggest that the coastal basalts, rather than being locally erupted, may be the westward extension of plateau basalts derived from eastern Oregon and Washington.

The local-origin hypothesis is based largely on the interpretation of coastal dikes and sills as representing vent areas; however, a complex mechanism, as yet unsatisfactorily defined, would be required to cause the eruption of virtually identical magmas simultaneously from source areas 500 km apart.

This study, therefore, has investigated the coastal basalt …