TEMPORAL AND GEOGRAPHIC EXTINCTION PATTERNS OF LATE DEVONIAN (LATE AND LATEST FRASNIAN) PLATFORM SHELLY FAUNAS: KELLWASSER MASS EXTINCTION BIOEVENTS: WESTERN LAURUSSIA

Detailed records of benthic platform and deep-water shelly faunas spanning the late Frasnian-early Famennian (Late Devonian) from subtropical and near equatorial tropical sites in western Laurussia document two step-wise late Frasnian extinction events (Lower and Upper Kellwasser bioevents). Rapid deepening associated with the crisis of the Lower Kellwasser event resulted in platform backstepping and coincides with significant collapse in brachiopod species biodiversity (up to 70% and higher) at all sites. Near total extinction of subtropical platform colonial rugose corals faunas in the late Frasnian of southern New Mexico is documented, although Frasnian rugosan biodiversity in western Canada actually peaks in the near-equatorial Kakisa Platform (NWT) following the initial wave of extinction associated with the Lower Kellwasser bioevent. At all sites Atrypoid and pentameroid brachiopods persist into the very late Frasnian. Strophomenoids persist only in the subtropical sites and appear to be extinct in the equatorial tropical sites at that time. Those groups as well as colonial rugosans suffered extinction during the Upper Kellwasser crisis interval in the very latest Frasnian. Moderately diverse rugosan faunas persist in the Iowa Basin at this time. Highstand resulted in platform progradation and emergence at three of four sites in the latest Frasnian-early Famennian. Very latest Frasnian crisis faunas discovered at Ancient Wall in western Alberta are dominated by rhynchonelloid, productoid, and cyrtospiriferid brachiopods similar to early Famennian survivor faunas. Athyroids join these elements in the survival interval at Ancient Wall in the earliest Famennian Sassenach Formation. Somewhat younger survivor faunas also occur at the New Mexico (San Andres Mts.) and NWT (Trout River) sites. They feature Orthoid and Orthotetoid genera common to survivor faunas recently reported by Bratton and Day (Great Basin), Day and Over (Appalachian Basin), and Balinski (southern Poland).