A LITHOSTRATIGRAPHIC AND MAGNETOSTRATIGRAPHIC FRAMEWORK IN A GEOCHRONOLOGIC CONTEXT FOR A PURPORTED PERMIAN–TRIASSIC BOUNDARY SECTION AT OLD (WEST) LOOTSBERG PASS, KAROO BASIN, SOUTH AFRICA

Current models of the terrestrial response to the end-Permian crisis are based largely on lithostratigraphic, magnetostratigraphic, and biostratigraphic records obtained from the Karoo Basin, South Africa. These successions have been interpreted to represent continuous sedimentation across the upper Daptocephalus and lower Lystrosaurus vertebrate-assemblage zones of the Balfour and overlying Katberg formations, respectively. The stratigraphic section at Old (West) Lootsberg Pass, Eastern Cape Province, is used as a cornerstone for the currently accepted model correlated with the marine extinction event, in part, based on a magnetic polarity stratigraphy of limited documentation. We provide a refined stratigraphic framework, encompassing over 740 m of measured section, compiled from twelve, closely spaced and physically correlated localities, across a northwest to southeast distance of less than 2 km. This framework is placed into magnetostratigraphic context and constrained by two U-Pb ID-TIMS age dates.

The Old Lootsberg Pass succession does not record continuous sedimentation, as previously argued. Several, rather than one, intraformational pedogenic-nodule conglomerate-lag deposits, which represent periods of landscape degradation, are contained in the upper Daptocephalus Assemblage Zone, ~100 m stratigraphically below the Katberg Formation. An interlaminated lithofacies, previously used as a diagnostic feature of the terrestrial event, occurs isolated at several stratigraphic positions, indicating that it is neither unique nor mappable. A dominant signature of normal-polarity magnetozones in the section is interrupted by two, short reverse-polarity intervals which are restricted to siltstone beneath erosional contacts with fluvial sandstones, indicating their cryptic nature of the succession. We have two dates indicated by U-Pb zircon age constraints from the section: one Early Changshsingian maximum age date from an ashfall (syndepositional) bed; and a Wuchiapingian maximum-age estimate for a detrital zircon population. A synthesis of our observations from Old (West) Lootsberg Pass with global patterns reported from the marine realm leads to the conclusion that the turnover from the Daptocephalus to Lystrosaurus AZs is not coincident with the end-Permian marine event.