The rocks of the Mississippian System in this region were formed by sedimentation on the edge of the craton, across a hinge zone, and on the eastern flank of the miogeosyncline. The Kinderhook and Osage Series are represented by the western-derived Milligen argillaceous sediments in the miogeosyncline and the Madison Group carbonates up to 2,000 ft thick on the craton. The Meramec and Chester Series consist of the 4,000-ft-thick White Knob Group carbonates in the miogeosyncline and a sequence less than 1,000 ft thick on the craton including: the uppermost Madison carbonates and evaporite cycles; a post-Madison erosion surface; and the Big Snowy Group shale and associated limestone. These major stratigraphic changes across the region are interpreted in terms of differentia paleotectonism across the hinge zone or the "Wasatch Line."

Through petrographic study the carbonate strata have been subdivided into a succession of interrelated carbonate sandstone and mudstone deposits with distinctive grain assemblages, depositional fabrics, and bedding or cycle types. Record of a Kinderhook, Osage, and early Meramec regression on the craton is present in the Madison Group sequence which includes Lodgepole calcitic and argillaceous mudstone, Mission Canyon bioskeletal sandstone, algal limestone, evaporite cycles, and an unconformity. In the lower White Knob strata of Meramec age, regression in the miogeosyncline is recorded by the sequence which includes the Middle Canyon siliceous carbonate mudstone, and the Scott Peak crinoid-bryozoan sandstone, oolite, algal sediments, and carbonate mudstone with intertidal zone(?) open space structures. The upper White Knob strata of Chester age are principally carbonate mudstone, which is divided into the South Creek and Surrett Canyon Formations and reflects a transgressive deepening of the Late Mississippian sea. Internal changes within the formations in the vicinity of the hinge zone suggest a shoaling or erosional event in this area, at least as early as middle Mississippian time.

New petrographic and stratigraphic evidence suggests that the carbonate sequences developed as a low slope "prograding shoal" complex, which advanced from the paleobathymetric highs into deeper areas of the craton and into the bathymetrically deep (starved) geosyncline. Biostratigraphic evidence limits the slope of the prograding surfaces to very low angles; the large stratigraphic units are approximately isochronous as indicated by preliminary study of the corals, conodonts, and endothyrids. It is inferred that the cratonic area was a bathymetric high, and that its shallows localized the first carbonate sedimentation in the region. The paleotectonic and paleogeographic importance of the hinge zone during the Mississippian Period is evidenced by major differences in sedimentary

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history on either side of it and internal changes of formations extending into it.

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