TIMING OF LATE GIVETIAN-EARLY FRASNIAN (MIDDLE AND LATE DEVONIAN) SEA LEVEL EVENTS SUBTROPICAL CRATONIC CARBONATE PLATFORM DEVELOPMENT: CENTRAL NORTH AMERICA

Three significant marine flooding events controlled the development of very late Givetian and early Frasnian carbonate platform and mixed carbonate-clastic shelf facies in the Iowa Basin. The initial late Givetian marine flooding of Devonian Transgressive-Regressive (T-R) cycle IIb (Johnson and others) during the norrisi conodont zone (Allanella allani brachiopod Zone) is recorded by a transgression of the middle and inner carbonate platform facies of the Andalusia and Osage Springs and lower Idlewild members of the lithograph City Formation in eastern and central Iowa, and the upper part of the Callaway Limestone of the Upper Cedar Valley Formation in central and eastern Missouri. Marine flooding during Frasnian Montagne Noir (M.N.) Zone 3 (Iowa Basin Strophodonta callawayensis Zone) initiated deposition of the upper Andalusia and upper Idewild members of the Lithograph City Formation in Iowa and Snyder Creek Shale in Iowa and Missouri, respectively. This flooding coincides with Devonian T-R cycle IIb-2. The widespread occurrence of brachiopod faunas of the Orthospirifer missouriensis Zone with conodonts of M.N. Zone 4 mark the flooding that initiated a second major early Frasnian transgression across the mid-continent carbonate platform. In eastern Iowa, this flooding event coincides with the base of the Buffalo Heights member of the Lithograph City Formation, and a major marine starvation surface at the top of the New Bloomfield beds in the lower half of the Snyder Creek Shale in central Missouri. The later major early Frasnian flooding event can correlated with continental margin successions in western North America, and provides a regional record of a potential global event permitting subdivision of Devonian T-R cycle IIb-2 of Day and others.