LOWER MISSISSIPPIAN SEQUENCE STRATIGRAPHY ACROSS THE USA

Sedimentary beds of the Madison type section at Monarch, Montana were traced to Cadomin, Alberta; Shell, Wyoming; Mingus Mountain, Arizona; Hannibal, Missouri; and Bowden, West Virginia. The primary tools of correlation were photographs of exposures with chemical weathering predominating and petrographic study using the Dunham classification of limestones.

Sedimentary couplets began with a resistant coarse bed of limestone with a sharp base. The top of the bed is a transition to a recessive silty bed with fine detrital quartz in fine-grained limestone. The couplet ends at a sharp contact, probably a diastem. Climatic cycles and sea level change are proposed as an explanation of the couplet's origin. The coarse beds are light colored while the fine beds are dark. Photographic study of exposures with chemical weathering shows remarkable bed persistance. Distinctive beds and patterns are very useful for reliable correlations; however, problems arise because lateral changes in the environment produce facies changes.

Sequence stratigraphy is a skill requiring many good exposures. The resulting correlations from couplet study should parallel those based on members and formations. Fossil study is best along depositional strike, particularly in the bryocrinoidal facies.

Summary:

1) Central Montana and Northern Wyoming: Woodhurst and lower Mission Canyon members of the Madison formation-resistant beds of crinoidal and oolitic limestone-recessive beds of pelleted and laminated silty limestone.

2) Foothills of the Canadian Rockies: Upper Banff (Plains) and Pekisko-resistant beds of bryocrinoidal limestone grade northeast to dolomitized wackestones-cherty recessive beds of silty to shaly dolomite.

3) Mingus Mountain, Arizona: Redwall-above the Whitmore Wash member the section becomes more red and silty. The overlying massive limestones of the Mooney Falls member becomes sandy.

4) Mississippian Type Section: Quarry and roadcut exposures show the Fern Glen, Dolby Creek, Haight Creek and Cedar Fork members of the Burlington formation-recessive units are fine grained, cherty, and dolomitic-resistant beds are massive white bryocrinoidal limestone.

6) West Virginia: Bowden-Greenbrier Limestone. The sequence stratigraphy is similar to the other areas, but the coarse beds are sandy and the silt beds are red with large mud cracks and ripple marks.