Columbia River Basalt Stratigraphy in Oregon |
In Cooperation with the Oregon Water Resources Department |
Skip site navigation bar and go to main content
CRBG Stratigraphic Nomenclature Chart Importance of Understanding CRBG Stratigraphy Contact |
StratigraphyThe CRBG has been divided into six formations: Imnaha Basalt, Picture Gorge Basalt, Prineville Basalt, Grande Ronde Basalt, Wanapum Basalt, and Saddle Mountains Basalt by Swanson and others (1979). These formations are divided into members and further subdivided into flow units based on field mapping, well logs, aeromagnetic surveys, geochemistry, and magnetic polarity. Flows belonging to the Imnaha Basalt, the oldest known in the Columbia River Basalt Group, are found in western Notes on geologic logs of the Columbia River Basalt Group: Field mapping, subsurface well logs and samples, aeromagnetic surveys, and paleomagnetic and geochemical studies are used to identify and assign individual flows to formations, members, and flow units in the Columbia River Basalt Group. With detailed study and mapping of the CRBG, revisions are made in the classification of individual basalt flows. The naming convention used in this website is based on work by Swanson and others (1979a) with revisions by subsequent investigators. The diagram of formations, members, and units represents the current stratigraphic nomenclature of the CRBG (Reidel and others, 2002). The naming classification shown provides a framework to identify and group individual basalt flows. It contains informal and formal geologic names.
The Ellensberg Formation includes unidentified sedimentary interbeds within the CRBG. Where the interbed is identified, the interbed name, for example, "Vantage," is used. (See photo at right.) Within the detailed subdivisions of the CRBG, multiple flows may occur. Individual flows are numbered consecutively within the subdivision starting with the uppermost flow in a series of flows. The numbering sequence is unique to each site and is not intended for correlation of individual flows between sites. The geologic logs and geochemical tables are presented as received from the geologists who interpreted the geologic data. The geologists assigned the geologic names and elevation of formations. In some cases, the elevation of the top and bottom of geologic units is referenced to sea level and in other cases is referenced to land surface. References Reidel, S.P., Johnson, V.G., and Spane, F.A., 2002, Natural gas storage in basalt aquifers of the Columbia Basin, Pacific Northwest USA--A guide to site characterization: Richland, Washington, Pacific Northwest National Laboratory. Swanson, D.A., Wright, T.L., Hooper, P.R., and Bentley, R.D., 1979, Revision in the stratigraphic nomenclature of the Columbia River Basalt Group: U.S. Geological Survey Bulletin 1457-G, 59 p. |
||
|
Oregon Water Science Center Studies Page Oregon Water Science Center Home Page |