Carbonate sedimentation on the Mississippian Mission Canyon platform: Response to tectonism and sea level fluctuations
1992
Deposition of the Mission Canyon Limestone in the northern Bighorn Basin region occurred in a dynamic, shallow, equatorial, platform sea. Twelve microfacies, grouped into three major facies associations (supratidal-upper intertidal, lower intertidal-subtidal and platforms interior shoal-sand bar), are recognized. The three members of this formation record distinct depositional episodes probably related to waning and then increasing tectonic activity in the Antler foreland basin and Central Montana trough. The vast, dolomitized tidal flats in the Bighorn Mountains suggest deposition of the Big Goose Member during quiescence. Correlative deposits in the Beartooth Mountains are thin grainstones separated by thick intervals of peritidal lime micrites. Increased tectonic activity during deposition of the Little Tongue and Bugg Ridge Members is suggested by greater abundance of subtidal and shoal deposits with smaller, discrete tidal flat deposits at all sections. Emergence early during deposition of the Bull Ridge Member is suggested by the presence of solution-collapse breccias near its base in the Beartooth Mountains and by the occurrence of siliciclastic materials (windblown continental detritus ) in the basal carbonate mudstones in the Bighorn Mountains and Elk Basin. Dolomitization and brecciation patterns suggest that some of the breccias, particularly in the Big Goose Member, formed during periodsmore » of nondeposition and subaerial exposure during Mission Canyon time and not during post-Madison emergence. Fourteen depositional sequences are recognized in the Mission Canyon. Some of their boundaries reflect migration of adjacent sedimentary environments through time. At others, juxtaposition of tidal flat facies on shoal deposits or shoal facies on tidal flat deposits suggests fairly rapid relative sea level changes.« less
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