Hydrocarbon Potential of Columbia Plateau--an Overview

Newell P. Campbell

The Columbia basin, one of the largest frontier provinces in the United States, encompasses approximately 160,000 km² in Washington, Oregon, and Idaho. Sedimentary rocks of the basin are overlain by ~4,500 m of the Miocene Columbia River basalt.

Five distinct areas of layered pre-basalt rocks, ranging in age from Precambrian to Miocene, crop out along the margin and probably extend under the basalt. Tertiary fluvial and volcaniclastic sediments are arranged in fault-bounded basins along the northwestern margin. The northern margin exposes Paleozoic marine sedimentary and metamorphic rocks associated with the Kootenay arc, whereas Precambrian Belt metasediments belonging to the Belt basin occur on the eastern margin. Mesozoic oceanic and volcanic arc rocks, overlain by Tertiary volcaniclastics, dominate the southern margin, and the southwestern margin is composed of Tertiary volcaniclastics and lavas. Both southern and southwestern margins are associated with the northeast-trending Columbia (Blue Mountain) arc.

Adequate hydrocarbon source rocks exist in at least three areas but good reservoir rocks are less abundant. Recent basin exploration has focused on the Yakima foldbelt subprovince where coal from fluvial-deltaic rocks accounts for all discovered gas to date. Sedimentary rocks from the northwest margin can be correlated with sub-basalt rocks in four new exploration wells. The distribution of these sedimentary rocks is apparently controlled by two major structures--the Hog Ranch axis and the White-Naches fault zone.

AAPG Search and Discovery Article #91040©1987 AAPG Rocky Mountain Section Meeting, Boise, Idaho, September 13-16, 1987.