KELLWASSER EXTINCTION RECORDS FROM DEEP CARBONATE RAMP AND SHALLOW PLATFORM SETTINGS IN CENTRAL NORTH AMERICA

New high resolution faunal data document the Lower Kellwasser extinction intervals (LKE) in deep subtidal ramp and platform settings in core and surface exposures in the Iowa Basin of the central United States. Benthic shelly and pelagic faunal sequences in deep-subtidal mid-ramp facies of the Amana Beds of the Lime Creek Formation record the LKE extinction. The Amana Beds pre-LKE benthic shelly faunas occur with offshore conodonts including Palmatolepis winchelli, Pa. foliacea, and Ancyroganthus assymetricus. The Amana Beds brachiopod sequence records stepped extinctions with no carryovers into the post-LKE interval. One of three ammonoids ranges through the LKE interval marked by deepening very high in Frasnian Zone (F.Z.) 12, followed by onset of benthic hypoxia and deposition of organic-rich brown shale deposits with the lowest Pa. bogartensis (lower F.Z. 13a). New data from Lime Creek platform sections in its type area in Floyd and Cerro Gordo counties and the Bruns Quarry (Butler Co.) provide a high-resolution record through the LKE interval in northern Iowa. New conodont occurrence of Palmatolepis foliacea and Pa. winchelli with diverse brachiopod faunas in the upper Cerro Gordo Member confirm an upper F.Z. 12 position at Bird Hill. At the Bruns Quarry the LKE is recorded in deposits of the Owen Member deposited during the late highstand of Devonian T-R cycle IId-1, followed by the onset of transgression, maximum flooding, and early highstand interval in the remainder of the Owen. Diverse brachiopod faunas (up to 30 species) of the Elita inconsueta Zone with upper F.Z.12 conodonts (Polygnathus planarius, P. brevilaminus, Ancryognathus amana, Ag. asymmetricus), in the upper Cerro Gordo and lower Owen are replaced by low diversity shelly assemblages of the Iowatrypa owenensis Zone associated with diverse F.Z. Zone 13a conodonts (Pa. bogartensis, Po. brevicarina, Ozarkodina dissimilis). Benthic assemblages from strata between the LKE and UKE intervals are dominated by infaunal bivalves and gastropods (Floyda & Westerna); with brachiopods including I. owensis, Pseudoatrypa devoniana, Spinatrypa trulla, Cyrtospirifer whitneyi (owenensis morphotype), Conispirifer cyrtinaformis, Nervostrophia sp. & Strophonelloides reversa; and rugose corals Tabulophyllum expansum and Pachyphyllum dumonti.