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Bear Gulch Limestone

The Bear Gulch Limestone in Montana is a fossiliferous lagerstätte, a limestone layer laid down in the Bashkirian Stage of the early Pennsylvanian epoch of the Carboniferous period, about 318 mya.This lens of limestone was laid down in a surrounding matrix that indicates a landscape of mudflats and braided channels (linear sandstone seams) in fresh and brackish water, in an arid climate (gypsum formation).