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The Ordovician carbonate sequence in northern Arkansas consists, in ascending order, of the Cotter, Everton, Joachim, Plattin, Kimmswick, and Fernvale formations. A comparison of the rock types, sedimentary structures, and faunal assemblages of these rocks with those of recent carbonate sediments indicates that these ancient rocks may be subdivided into lithofacies that are similar to modern supratidal, intertidal, and subtidal facies. Further comparison of these lithofacies with an epeiric sedimentation model shows that (1) the Cotter Dolomite, Joachim Dolomite, and Plattin Limestone were deposited chiefly in supratidal and intertidal environments, (2) the Everton Formation was deposited chiefly in an intertidal environment, and (3) the Kimmswick and Fernvale Limestones ere deposited in protected to open subtidal environments, above wave base.
Two major unconformities in the sequence, each overlain by a sandstone (Kings River Sandstone Member of the Everton Formation and St. Peter Sandstone), probably are the result of the widespread epeirogenic movements that initiated development of the sub-Tippecanoe unconformity. Earlier workers have reported paraconformities and microdisconformities within the post-St. Peter sequence that supposedly represent periods of subaerial exposure and erosion. Our premise is that these surfaces were integral to the sedimentary environments and were, in fact, developed by shifts in laterally adjacent, coexisting facies; these shifts were not related to uplift or to subaerial exposure of preexisting rocks.
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