AN INTEGRATED PALAEOENVIRONMENTAL ANALYSIS OF THE PERMO-TRIASSIC BOUNDARY SUCCESSION IN EASTERN AUSTRALIA

This paper provides initial results from ongoing research aimed at elucidating the timing, duration, and causes of the end-Permian mass extinction (EPME) in eastern Australia. This succession was accumulated in a continental margin setting, which contrasts with most previous studies of the EPME that were located in deep marine or continental interior settings. Our study also differs from earlier work in that it represents an extensive, high to mid-palaeolatitude transect (70-40 degrees south). The succession is constrained by a large body of new, precise, absolute ages (CA-IDTIMS method) that allow resolution of timeframes at unprecedented levels of detail. These factors allow a number of questions to be addressed: 1. Did the EPME occur precisely at the Permo-Triassic boundary at 251.9 Ma?, 2. Was the terrestrial extinction in eastern Australia synchronous with the marine extinction?, 3. Were major environmental changes synchronous with the EPME and with the Permo-Triassic boundary?, 4. What environmental factors were the probable drivers of the EPME in eastern Australia, and 5. Which biophysical-climate feedbacks led to amplification of the environmental stresses? The eastern Australian succession is stratigraphically complete, and preserves the entire Permian system in addition to the Lower and Middle Triassic. Previous work by us has established that icehouse conditions of the late Palaeozoic Ice Age persisted longer in eastern Australia than in other regions of Gondwana. Indeed, the new geochronological data indicate that the ice age extended into the Late Permian, after the initial faunal extinction at the Guadalupian-Lopingian boundary, and only ~ 2 m.y. before the EPME at 251.9 Ma. This suggests that the EPME may represent a final biological tipping point at the end of a protracted interval of increasingly severe paleoenvironmental conditions associated with the transition from late Palaeozoic icehouse to Mesozoic hothouse conditions. Initial results suggest that the main biotic turnover was not synchronous with the Permo-Triassic boundary, and that major changes in palaeoenvironmental conditions did not occur until somewhat later. This suggests that the EPME may have occurred somewhat later in high palaeolatitudes than elsewhere.