Waulsortian-Type Carbonate Banks in the Mississippian Lodgepole Formation of Central Montana

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Abstract
Several Waulsortian-type carbonate banks nearly 200 feet thick and about 1/4 mile long occur in the Mississippian Lodgepole formation in the Big Snowy Mountains of central Montana. Compositional layering extends through all parts of the banks, with depositional attitudes up to about 35°. The layering results from variations in the amount of skeletal material and sparry calcite diluting the calcilutite matrix. Although depositional relief was as much as 150 feet on steep slopes of lime mud and silt, no biotic constituent yet found was responsible for growth and development of the banks. Fenestrate bryozoans and crinoids are the most abundant faunal constituents, and there are minor quanities of brachiopods, mollusks, and Stromatactis. Development of the banks may have begun from separate growth centers, and in one bank unit an early bank generation was subsequently engulfed by a later stage. Major postdepositional events included the formation and filling of large dilatational fissures and of irregular cavelike openings.

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