A Precambrian diamictite below the base of the Stillwater Complex, southwestern Montana

Randolph Koski; Norman J. Page

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USGS · 70161756

A Precambrian diamictite below the base of the Stillwater Complex, southwestern Montana

Randolph Koski·Norman J. Page

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Abstract

The metasedimentary rocks of Precambrian age below the base of the Stillwater Complex, southwestern Montana, contain a metamorphosed diamictite similar to diamictite in strata of late Precambrian and Early Cambrian age in Canada and the Western United States. The diamictite consists of a quartz-cordierite matrix containing an average 10-15 percent of rock fragments diverse in shape, size, angularity, lithologic types, and textures. The diamictite unit is poorly sorted, crops out discontinuously for 14 miles, and locally has a crude layering containing dropstones. Its origin is debatable, but the rock is suggestive of glacial marine deposition. The minimum age of the diamictite of the complex is 2,750 m.y. from U-Pb determination on zircon of intrusive quartz monzonite, the maximum 3,140 m.y. as determined on zircon from metasedimentary rocks interbedded with the diamictite.

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Journal of Research of the U.S. Geological Survey Article

Source-reported bounding extent: 45.079339209738094° to 46.164614496897094° latitude; -110.49774169921875° to -108.92669677734374° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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BibTeX RIS

Randolph Koski, Norman J. Page. 1973. A Precambrian diamictite below the base of the Stillwater Complex, southwestern Montana. https://pubs.usgs.gov/publication/70161756

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