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Paleomagnetic studies resolve stratigraphic and correlational problems of several ignimbrites exposed along the margins of the eastern Snake River Plain (ESRP) in eastern Idaho and western Wyoming. Each ignimbrite exhibits a consistent magnetic remanence direction from its base to top. All units studied are high-silica, densely welded, metaluminous ignimbrites, the radiometric ages of which range from 7 Ma to 4 Ma. This study investigates whether ignimbrites of the Heise volcanic field—the tuffs of Blacktail Creek, Blue Creek, Elkhorn Spring, and Kilgore—correlate with the lithologically and chronologically similar Walcott and Conant Creek tuffs, two ignimbrite sheets marginal to the Heise field.

Correlation of the tuff of Elkhorn Spring with the tuff of Blue Creek appears to be erroneous. Rather, paleomagnetic and chemical data indicate that the tuff of Blue Creek is equivalent to the Walcott Tuff. Results also suggest that the Conant Creek Tuff may actually consist of two separate ignimbrites: (1) an older unit that is tentatively correlated with the tuff of Elkhorn Spring and (2) a younger unit that is correlative with the tuff of Kilgore. The older unit appears to be restricted to the Heise cliffs and to the west side of the Teton Range. The tuff of Blacktail Creek remains a separate older unit.

The Blue Creek and Kilgore calderas are now recognized as sources for the Walcott Tuff and the younger Conant Creek Tuff. The source of the older Conant Creek Tuff remains unidentified. Minimal areal distribution estimates are 15,000 km2 for the Walcott Tuff and 18,000 km2 for the tuff of Kilgore.

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