Abstract

Shatter cones that point steeply upward are present in abundance over an area >100 km2 in Belt Supergroup sandstone outcrops in Beaverhead County, southwestern Montana. Crushed sandstone with fragments dispersed in a fluidal textured, cryptocrystalline matrix of similar chemical composition has also been found. Absence of cones in adjacent units of Mississippian and younger age suggests a late Precambrian-early Paleozoic age for the formation of this newly discovered impact structure, only a small part of which is preserved in the complexly faulted terrain.

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