Red Butte Conglomerate. A Thrust-Belt-Derived Conglomerate of the BeaverheadGroup, Southwestern Montana

摘要

The Red Butte Conglomerate is herein defined as the uppermost formation of theBeaverhead Group. The Red Butte includes dominantly limestone conglomerate and minor interbedded sandstone and siltstone shed from the frontal thrust belt in southern Beaverhead County, Montana. The Red Butte can be distinguished from the Lima Conglomerate and other similar conglomerates of the Beaverhead Group by the included clasts of recycled limestone conglomerate and an admixture of well-rounded quartzite clasts recycled from older quartzite conglomerates of the Beaverhead. The Red Butte Conglomerate overlies a sequence of older Beaverhead limestone conglomerate and quartzite conglomerate with angular discordance, and it is cut by the frontal Tendoy thrust system from which it was largely derived. East of the Tendoy Mountains in the Sage Creek basin, the Red Butte Conglomerate is overlain unconformably by Tertiary sedimentary and volcanic rocks of the Sage Creek basin.