LATE FRASNIAN KELLWASSER EXTINCTIONS CONSTRAINED BY INTEGRATED CONODONT-BRACHIOPOD-AMMONOID BIOSTRATIGRAPHY, ISOTOPE CHEMOSTRATIGRAPHY, MAGNETOSTRATIGRAPHY AND ASTRONOMICAL CYCLOSTRATIGRAPHIC CALIBRATION: IOWA BASIN-WESTERN LAURUSSIA

New faunal, chemostratigraphic and magnetostratigraphic data document the Lower and Upper Kellwasser extinction intervals (LKE & UKE) in basinal, deep subtidal ramp and platform facies in core and surface exposures in the Iowa and western Illinois basins. Conodont sequences in the Iowa Geological Survey (IGS) Sullivan and H-32 cores fix the position of the LKE in the upper Hog Thief Member (new) of the Sweetand Creek Shale high in Montagne Noire (MN) Zone 12, and the UKE beginning within MN Zone 13b in the lower Grassy Creek Shale in IGS Sullivan Core in southeastern Iowa. Spectral analysis of magnetic susceptibility data from the IGS CG-1 (platform) and H-32 (basinal) cores confirm that the onset of the LKE extinction begins within the interval of Frasnian Long Eccentricity Signal 15 (FR-LES) and the UKE interval is high within FR-LES 16 (recently documented in Frasnian of western Alberta). Conodont, brachiopod and ammonoid sequences in deep-subtidal mid-ramp facies of the Amana Beds of the Lime Creek Formation record the LKE extinction demonstrated by the stepwise extinction of brachiopods and ammonoids within transgressive and maximum flooding interval associated with Devonian Transgressive-Regressive (T-R) cycle IId-2. The onset of LKE begins in the upper part of MN Zone 12, manifested by disappearance of all benthic shelly megafauna (brachiopods, echinoderms, molluscs, trilobites) and two of three ammonoid species just below the base of MN Zone 13a coinciding with maximum flooding and organic-rich brown shale deposition. The Lime Creek Formation in the CG-1 core in northern Iowa records the onset of the LKE δ¹³C_carb excursion within FR-LES 15 within MN Zone 12 (upper part of brachiopod Elita inconsueta Zone). At the Bruns quarry in northern Iowa, the LKE is recorded in deposits of the upper Cerro and Owen members of the Lime Creek deposited during the late highstand of T-R cycle IId-1, followed by the onset of transgression, maximum flooding, and early highstand interval of T-R cycle IId-2 in the remainder of the Owen Member. Diverse brachiopod faunas of the upper Cerro Gordo and lower Owen members (with conodonts of upper MN 12) are replaced up section by low diversity shelly fossil assemblages dominated by gastropods and infaunal bivalves, with the brachiopod Iowatrypa owensis and associated conodonts of MN Zone 13a.