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 Stratigraphy (mappable units) of the Columbia River

Basalt Group (CRBG)

As this chart to the right shows, the CRBG has been divided into a host of regionally mappable units based on variations in physical, chemical, and paleomagnetic properties (N= normal polarity, R = reversed polarity, E = excursional polarity, and T = transitional polarity) - in regard to stratigraphic position (sequence) - that exist between flows and packets of flows.

In the Umatilla Basin area the CRBG is represented mostly by three formations, from youngest to oldest, the Saddle Mountains, Wanapum, and Grande Ronde Basalts.

These formations can further subdivided into a number of members defined, as are the formations, on the basis of a combination of unique physical, geochemical, and paleomagnetic characteristics.

These members can be, and often are, further subdivided into flow units.

Last Updated ( Thursday, 19 March 2009 )
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