Deep time records provide evidence for changes in biodiversity and ecosystem disruption and recovery, and act as models for understanding the potential changes now recognized affecting Earth. The End Permian Mass Extinction Event is reported to have impacted more than 90% of life in the oceans and up to 80% of life on land, with the collapse occurring simultaneously at 252.2±0.2 million years ago. Recent work of the PI and collaborators demonstrates that the paleontological records from the Karoo Basin, South Africa, on which the idea of sudden collapse on land is based, can not be used to identify a distinct event. Rather, criteria used to assign an end-Permian age to the biological patterns are inaccurate based on field relationships. The most reliable way to identify the timing of this event is by using chronometric techniques based on radiometric dating of single crystal zircons from volcanic ash deposits. To date, this has not been possible because it was believed that such deposits didn?t exist near the boundary. A fossilized forest litter, located 70 m below the level where the extinction event is reported, is buried and preserved by volcanic ash deposits in Wapadsberg Pass, Eastern Cape Province. A pilot study of single crystal zircons analyzed by isotope dilution thermal ionization mass spectrometry (ID-TIMS) using the ET535 tracer (spike) solution, distributed by the EARTHTIME initiative, resulted in a suite of ages indicating a detrital source for the zircons. Ages range from the NeoProterozoic (1038.78 ± 1.42 to 606.76 ± 1.0 Ma [3 grains]) to the early Mesozoic (252.0 ± 0.5 to 251.8 ± .038 Ma [3 grains]). The project goals include the acquisition of a larger suite of detrital zircon from several stratigraphic horizons in Wapadsberg Pass and elsewhere that will be age dated. These will be correlated with changes in sedimentary environments in the collection sites to place an age constraint on the biodiversity trends identified in the Karoo Basin. The project tests the hypothesis that the ?Mother? of all Mass Extinctions was a phenomenon restricted to the oceans, and changes in biodiversity trends on land were decoupled from those documented elsewhere. If turnover in continental biodiversity did not happen simultaneously with the patterns identified in the oceans, a new model for the greatest mass extinction in Earth history will have to be developed.

Project Report

The end of the Paleozoic Era, ~252 million years ago, witnessed the greatest biodiversity loss in Earth's history. Ocean life was reduced up to 90% by some estimates, and life on land also is believed to have been affected similarly. Fossils collected from rocks exposed in the Karoo Basin, South Africa, are used as the keystone to understand how terrestrial plants, and the vertebrate food web they supported, responded to the ecosystem crisis. For more than a half century, it has been assumed that the extinction of reptiles and amphibians, here, occurred at the same time as the demise of marine animals across the globe. In rocks that represent ocean sediments it is possible to correlate the marine events in both the northern and southern hemispheres. This is possible because rocks, now exposed on different continents, preserve biological and chemical records that can be understood using a variety of paleontological and geochemical techniques. In addition, the timing of the crisis now is known through age dating of volcanic-derived zircon crystals, using high precision analytical methods, derived from volcanigenic deposits in the marine rocks. To date, though, there are no age dates from the rocks that represent sediments deposited on the continents which allow for a direct connection between oceanic and terrestrial events. We have found volcanic-derived deposits in rocks of the Karoo Basin from below and above the ecological crisis, as understood on land based on changes in fossil-vertebrate assemblages. Age dates from these rocks provide the first evidence to test whether biodiversity loss on land and in the oceans was coincident and associated with the End-Permian extinction event. To date, age determinations on volcanic-derived zircon crystals from beds below the vertebrate-defined Permian—Triassic extinction event are Late Permian, whereas analyses continue on a volcanic ash bed situated above the extinction event. These rocks, and the stratigraphic sections in which they occur, have been analyzed for their remnant paleomagnetic signatures as a complementary data set which will allow comparison with the magnetostratigraphic record, and placement within a global context. But, newly discovered fossil plant and vertebrate collections call into question the response of life-on-land to the crisis as currently envisioned. We have collected new fossil plants from rocks above the vertebrate-defined Permian—Triassic extinction event which belong to the group of gymnosperms that colonized Permian wetland habitats across the southern hemisphere. These Glossoperis-rich floras also preserve the spores and pollen of other plant groups, known to be of Permian and Triassic age, some of which have been hypothesized to represent the recovery flora. Glossopteris leaves and the spore-and-pollen grains occur both below and above river deposits that, currently, are interpreted to represent a change in the landscape from wet to arid environments in response to the ecological crisis. But, new fossil wood and vertebrate remains also have been collected from conglomerate, comprised of reworked soil nodules, in the base of these river deposits. The fossil wood shows tree-ring evidence for moist, not arid, growth conditions, and the vertebrate skull is identified as belonging to the Late Permian, pre-extinction ecosystem. If the vertebrate-defined Permian—Triassic boundary in the Karoo Basin is valid, these new data demonstrate the continuance of a wetland ecosystem into the post-extinction landscape, requiring current ecosystem response models to be reevaluated. If vertebrate-defined Permian—Triassic extinction event in the Karoo Basin is either a younger (earliest Triassic) or older (Late but not latest Permian) phenomenon, its utility is severly reduced. As a result, it will be necessary to re-evaluate the terrestrial stratigraphic, paleontologic, and geochemic record to determine the consequences of the marine End Permian mass extinction on land.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Yusheng Liu
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Colby College
United States
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