COMPARATIVE STRATIGRAPHY OF THE UPPER ORDOVICIAN (SANDBIAN-KATIAN) SUCCESSIONS OF EASTERN MISSOURI AND CENTRAL TENNESSEE

Comparison of Upper Ordovician successions of eastern Missouri and central Tennessee is facilitated by previous recognition of the Deicke and Millbrig K-bentonites in both regions. Below the Deicke, the Platteville in Missouri and the lower Carters Formation in Tennessee comprise broadly comparable shallow subtidal to peritidal carbonate facies. In both regions, the Deicke itself was deposited upon a starved flooding surface that is overlain by a thin interval of subtidal, shaly facies that punctuates the carbonate successions. The Millbrig K-bentonite also sits on a starved, flooding surface that previous workers have interpreted as recording a major disconformity. In the St. Louis, Missouri, area, the Millbrig is succeeded by a succession of fine-grained siliciclastics and carbonates (Decorah) that is truncated by a significant disconformity beneath the Kimmswick Limestone. The lowermost Hermitage Formation near Nashville, Tennessee, is strongly condensed, including thin conglomerate composed of reworked clasts of mineralized hardgrounds, and supports previous suggestions that correlatives of the lower Decorah are missing in this region. The siliciclastics of the Hermitage contrast with coeval carbonates of the Kimmswick, which include subtidal bioturbated pack- and wackestone as well as higher energy, cross-bedded grain- and rudstone. This sharp interregional difference records the increasing significance of siliciclastic input in Tennessee as the Taconic orogen developed.