Biostratigraphic dating

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[In White Knob Mountains, Milligen and Copper Basin Formations as mapped by Nelson and Ross, (1969) are replaced in this report by Mc Gowan Creek.] Cross sections; isopach maps. and associated megafossils indicate Early Mississippian age. Fossils collected from black slaty shale at several localities in Pioneer Mountains, Blaine Co, ID in the Snake River basin. For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

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It places particular emphasis on those parts of the stratigraphic column where economic resources are important.

The Geologic Time Scale 2012 (GTS 2012 ), published by the Geologic Timescale Foundation , has been implemented as the standard geological timescale for use in Geoscience Australia.

All Australian biozonation schemes have been or are being recalibrated to GTS 2012 and their relationships to it are stored in Geoscience Australia's Timescales Database.

Named for exposures on ridge south of Mc Gowan Creek in N1/2 sec 28 and E1/2 sec 29, T12N, R21E, Doublespring 15-minute quad, Custer Co, ID in the Idaho Mountains province. Divisible into: 1) a lower member 3,175 ft thick composed of grayish-black, carbonaceous, noncalcareous to slightly calcareous, thin-bedded argillite, silty argillite, and siltite with interbeds of medium-gray, very fine to fine-grained, partly gritty to conglomeratic sandstone and quartzite and dark-gray, silty, micritic limestone, and 2) an upper member 470 ft (143 m) thick composed of dark-gray and pale-yellowish-brown, thin-bedded, calcareous siltstone interbedded with dark-gray, silty, micritic limestone. Correlation chart shows Mc Gowan Creek correlates with lower part of Copper Basin Formation in Pioneer Mountains.

Correlates with lower part of Copper Basin Formation.

Evidence suggests both units are fluviatile, and despite fossil leaves, complete lack of contemporaneous volcanic rocks in Swauk suggests units are of different ages. Is divisible into [at least] three lithological units that are (descending): (A) interbedded basalt, basaltic tuff and breccia, and arkosic sandstone with minor rhyolite tuff and flows, and andesite flows(?

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