The Columbia River Basalt Group: from the gorge to the sea

GSA Field Guides
By: , and 



Miocene flood basalts of the Columbia River Basalt Group inundated eastern Washington, Oregon, and adjacent Idaho between 17 and 6 Ma. Some of the more voluminous flows followed the ancestral Columbia River across the Cascade arc, Puget-Willamette trough, and the Coast Range to the Pacific Ocean. We have used field mapping, chemistry, and paleomagnetic directions to trace individual flows and flow packages from the Columbia River Gorge westward into the Astoria Basin, where they form pillow palagonite complexes and mega-invasive bodies into older marine sedimentary rocks. Flows of the Grande Ronde, Wanapum, and Saddle Mountains Basalts all made it to the ocean; at least 33 flows are recognized in the western Columbia River Gorge, 50 in the Willamette Valley, 16 in the lower Columbia River Valley, and at least 12 on the Oregon side of the Astoria Basin. In the Astoria Basin, the basalt flows loaded and invaded the wet marine sediments, producing peperite breccias, soft sediment deformation, and complex invasive relations. Mega-invasive sills up to 500 m thick were emplaced into strata as old as Eocene, and invasive dikes up to 90 m thick can be traced continuously for 25 km near the basin margin. Mega-pillow complexes up to a kilometer thick are interpreted as the remains of lava deltas that prograded onto the shelf and a filled submarine canyon southeast of Astoria, possibly providing the hydraulic head for injection of invasive sills and dikes at depth.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The Columbia River Basalt Group: from the gorge to the sea
Series title GSA Field Guides
DOI 10.1130/2009.fld015(32)
Volume 15
Year Published 2009
Language English
Publisher Geological Society of America
Contributing office(s) Geology and Geophysics Science Center
Description 38 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title GSA Field Guides
First page 737
Last page 774
Country United States
State Oregon;Washington
Other Geospatial Columbia River
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