Paper No. 76-18
Presentation Time: 9:00 AM-5:30 PM
LATEST FRASNIAN (UPPER DEVONIAN) LOWER KELLWASSER EXTINCTION (LKE) SUBTROPICAL CARBONATE PLATFORM SURVIVOR-RECOVERY FAUNA-CENTRAL NORTH AMERICA
Upper Devonian Lime Creek Formation platform sections in its type area in north-central Iowa provide a high-resolution faunal record through the LKE and post-Lower Kellwasser Extinction (LKE) interval. Important new data document the pre- and post-LKE interval in the Owen Member (Mb.) deposited during the late highstand phase of Euramerican Devonian T-R cycle IId-1, followed by the onset of transgression, maximum flooding, and early highstand of latest Frasnian Devonian T-R cycle IId-2 in the remainder of the Owen. The Lower Kellwasser extinction is marked by marked range terminations and disappearance of over 60% of the brachiopod species of the Elita inconsueta Zone in the interval of the uppermost part of Frasnian Zone (F.Z.) 12 in the upper Cerro Gordo Mb. and lower part of the interval F.Z. 13A in the lower half of the Owen Mb. The post-LKE brachiopod fauna in the middle and upper Owen Mb. is characterized by low diversity mollusc-dominated assemblages of the upper E. inconsueta and Iowatrypa owenensis zones associated with F.Z. Zone 13A conodonts. The occurrence of Iowatrypa owenensis within and well above the base of F.Z. 13A indicate realignment of the base of the I. owenensis Zone within F.Z. 13A post-LKE survivor-recovery interval. Benthic macrofossil assemblages from post-LKE subtidal platform deposits are dominated by infaunal bivalves including Edmondia sp., Paracyclus sp. and Spathella sp.; large archaeogastropods Floyda gigantea & Westerna gigantea; low diversity brachiopod assemblages with Iowatrypa owensis, Pseudoatrypa devoniana, Spinatrypa rockfordensis, Cyrtospirifer whitneyi (owenensis morphotype), Conispirifer cyrtinaformis, Rhipidomella sp., Floweria sp., Douvillina n.sp., Nervostrophia sp., Strophodonta (Strophodonta) n.sp., Strophonelloides reversa; and solitary and colonial rugose corals Tabulophyllum expansum & Pachyphyllum dumonti. No record of the Upper Kellwasser Extinction interval is preserved in the Iowa Basin inner and middle shelf facies tracts of the Lime Creek Platform due to emergence and erosion, or non-deposition of deposits spanning the very latest Frasnian-Early Famennian.