Mineralogy and geochemistry of continental shelf sediments of Washington-Oregon coast

Abstract

ABSTRACT An analysis of the mineralogy and geochemistry of continental shelf sediments offshore of the Washington-Oregon Coast indicates that three depositional areas are present on the continental shelf; these consist of a nearshore area including the lower portion of the Columbia River estuary and a main shelf area, both characterized by poorly sorted sediments, and a third area seaward of 80 fm which is characterized by glauconitic sediments. Within each area the mineral and chemical compositions of the sediments appear distinctive and characteristic for the area. The glauconite in the continental shelf sediments is generally found in the deeper shelf areas. It is derived from glauconitic-bearing Tertiary sedimentary rock units exposed in the area, some may be transported north from shelf areas off central and southern Oregon and some may be forming in place. Boron is associated with the glauconite and may be indicative of the presence of glauconite or as an indicator of the marine environment.