Eastern Australian climate-change and mass extinction in the Permian: Volcanic "Hell on Earth" 300-250 million years ago
Professor Ian Metcalfe (Earth Sciences, School of Environmental and Rural Science, University of New England) has for the last four years been leading an international research team applying high-precision Uranium-Lead zircon Chemical Abrasion Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-TIMS) dating of volcanic ash layers (tuffs) in Permian-Early Triassic (299-247 million years ago) sedimentary rocks in Eastern Australia. The project aimed to internationally calibrate the Permian-Triassic of Australia and also provide vital information on the age and age-duration of major deep-time climate-change and mass extinction events in high-latitude southern hemisphere Gondwana that feed into global debates on deep-time extreme climate-change (glaciations, greenhouse crises, global warming) and mass extinction events.
Permian sedimentary rocks in the Sydney, Gunnedah and Bowen basins of eastern Australia include abundant, geographically extensive and volumetrically large volcanic ashes (tuffs) derived from a major volcanic arc situated on the margin of eastern Australia. Major tuff layers reach up to more than ten meters in thickness and in some cases can be traced over wide tracts of Queensland and New South Wales. Many of the thick geographically extensive (many tens of thousands of square kilometers in the Sydney Basin alone) volcanic ash deposits (e.g. Awaba Tuff, Nobbys Tuff in NSW and Platypus Tuff and Yarrabbee Tuff in Queensland) can be regarded as the products of catastrophic Supervolcanos having a Volcanic Explosivity Index (VEI) of 8 or higher producing thousands of cubic kilometers of ash. Catastrophic volcanism was so frequent in the late Late Permian Newcastle Coal Measures of eastern Australia, 256-252.2 million years ago, that during this 3.8 million year period there are six VEI 8 eruptions with a frequency of ~600,000 years and approximately 200 tuff layers recorded of VEI 5 or above which indicates a frequency of cataclysmic volcanic eruptions, producing hundreds of cubic kilometers of ash, every 20,000 years. The Late Permian of eastern Australia can truly be described as volcanic hell on Earth!
The presence of multiple tuff layers in the Permian-early Triassic of eastern Australia allows precise dating of these and hence of indicators of major climate-change including glaciations, global cooling/warming, greenhouse crises (high levels of carbon dioxide in the atmosphere) and mass extinction events, including the end-Permian mass extinction, the largest known to science.
The research involved the extraction of tiny zircon crystals from tuff layers and the individual isotopic dating of these zircons using U238Pb206 and the current best practice annealing and chemical abrasion techniques that result in accurate high-precision (0.05% or better) ages for tuffs. The zircon dating was undertaken by team members Dr Jim Crowley and Professor Mark Schmitz at Boise State University, USA. The zircon dating method utilised is a refined version of that published by Prof. Metcalfe's team in 2004 in the journal Science based on work in China.
In the first major paper resulting from the study published in the journal Gondwana Research entitled "High-precision U-Pb CA-TIMS calibration of Middle Permian to Lower Triassic sequences, mass extinction and extreme climate-change in eastern Australian Gondwana" Metcalfe and his team provide a vital new temporal framework for and international calibration of Permian-Triassic rocks in Australia that contain immense energy resources (coal, oil, gas). The paper also demonstrates that the two youngest previously identified Permian glacial episodes in Australia are significantly younger than previously proposed and also concludes "The end-Permian mass extinction is essentially the same age in both terrestrial and marine sequences of high-latitude Gondwana and in low-latitude northern hemisphere marine and terrestrial sequences" and " A global climate-change scenario for the end-Permian mass extinction, involving combined multiple causative mechanisms, including massive volcanism (Siberian Traps), global warming (with global wildfires), methane release from clathrates, hypercapnia and oceanic anoxia and acidification, that occurred over a relatively short period of time (less than 0.5 my), is more likely than a single causative mechanism".
Contact:
Professor Ian Metcalfe, University of New England
Tel: +61-2-67726297
Email: imetcal2@une.edu.au