CONSEQUENCES OF THE SUDDEN COLLAPSE OF FORESTS ACROSS THE END-PERMIAN EVENT (252.3 MYA) – EVIDENCE FROM THE SYDNEY BASIN AUSTRALIA

The end-Permian event (EPE: 252.31 ± 0.07 million years ago) is the largest known biodiversity crisis in history of life. Although the dynamics of extinction in the marine realm are relatively well known, and with the Permian-Triassic GSSP established within a marine succession, data from plants is scant and the consequences of this event on terrestrial ecosystems remain poorly understood. In particular, the consequences of deforestation have not been considered.

The successions are part of the Newcastle/Illawarra Coal Measures, which comprise coal seams intercalated with siliciclastic sediments deposited in fluvial and deltaic systems. The Vales Point coal seam is the topmost coal seam in the northern part of the basin and is followed by the globally recognized post-extinction “coal-gap”, which continues well into the Triassic. High-resolution palynological investigations across a three meter section spanning the Vales Point coal seam exposed in coastal cliffs north of Sydney, Australia reveal abundant and well-preserved spore-pollen assemblages typical glossopterid forest-mire communities. Across the Sydney Basin, the interval overlying the top coal seam is represented by an approximately 1–5 m thick carbonaceous mudstone with coal intraclasts, but it is less complete along the cratonic margin of the basin within the Illawara Coal Measures south and west of Sydney.

The lowermost assemblage reflecting post extinction productivity occurs in a laminated mudstone c. 1.5 m above the Vales Point coal seam. The palynological assemblage in this succession is dominated by freshwater algae, and laterally at some places also by acritarch communities. Sea-level rise has been invoked by many authors to explain the global record of swarms of fresh- and brackish-water algae and acritarchs during the end-Permian event. However, comparisons with the consequences of recent deforestation show that this pattern of algal enrichment is consistent with the end-Permian evidence of ponding on alluvial plains as a response to the continent-wide disappearance of the glossopterid forests. Comparisons with sedimentological and palynological signals following the end-Triassic and end-Cretaceous mass extinction events reveals striking similarities in alluvial plain ponding.