WHERE IN THE KAROO IS CARMEN SANDIEGO’S LYSTROSAURUS DECLIVIS ASSEMBLAGE-ZONE BOUNDARY?
We present a new Karoo Basin model based on a multidisciplinary approach incorporating geochronology, magnetostratigraphy, palynostratigraphy and paleobotany into a stratigraphic framework spanning classic AZ-boundary localities from the Eastern Cape to the Free State provinces. We demonstrate that the diagnostic taxa used to distinguish pre-extinction and post-extinction vertebrate AZs are coeval, and coexisted on the same Changhsingian land surfaces. Diagnostic taxa of the Daptocephalus AZ are preserved in green mudstone whereas L. declivis AZ taxa are preserved in laterally correlatable reddish-gray mudstone. Our data show that both assemblages lived in a Glossopteris-dominated landscape. A new U-Pb CA-ID-TIMS age date constrains all of these elements to the latest Permian, ~0.3 Ma older than the marine event. We also demonstrate that the currently defined AZ boundary occurs in a normal polarity magnetozone in the Eastern Cape with an early Changhsingian age estimate (Lootsberg Pass) and in a reverse polarity magnetozone in the Free State (Bethel) province with a late Changhsingian age estimate. Our data negate the utilization of an isochronous horizon and vertebrate turnover in the basin and, by extension, across Gondwana and elsewhere.