Australia: The Land Where Time Began

A biography of the Australian continent 

Late Permian Mass Extinction - Recovery Impeded by Multiple Greenhouse Crises in the Early Triassic

Following the mass extinction event of the Late Permian, the most severe biodiversity known, the recovery period was unusually long, continuing through the Early Triassic. Discussion has continued on whether the delayed recovery was the result of especially profound ecological disruption or other environmental perturbations. New evidence has been found in the Sydney Basin, southeastern Australia, of 5 successive spikes of unusually high atmospheric concentrations of CO2 in the Late Permian and Early Triassic, as well as profound episodes of chemical weathering. These successive crises of greenhouse levels of atmospheric CO2 coincided with periods of unusually warm, wet palaeoclimates at a palaeolatitude of 61oS. The long-term cool, dry conditions with low atmospheric CO2 levels were punctuated by successive transient greenhouse crises, the authors1 suggesting that these crises may have contributed to the length of time for which the biota of the Early Triassic remained small and with low diversity.

After the greatest known mass extinction event at the end of the Permian the terrestrial plants and animals were of distinctive, cosmopolitan types. A few taxa of small to medium sized therapsids, especially Lystrosaurus (Cosgriff et al., 1982; Benton et al., 2004; Retallack et al., 2003) dominated the land animals of the time. The main plants were lycopsids (Tomiostribus and Pleuromeia) and the conifers such as Voltzia & Voltziopsis: White, 1986; Retallack, 1995; Visscher et al., 2004). There were small paper clams, Claraia, and there were many inarticulate brachiopods, Lingula (Hallam & Wignall, 1997; Fraiser & Bottjer, 2004; Twitchett, 2007). Within biotas diversity, biotic differentiation by region, swamp woodlands, reef corals and bryozoans didn't reach the levels they achieved in the Permian until the Middle Triassic (Retallack et al.,1996; Payne et al., 2004; Benton et al., 2004; Weidlich, 2007). This recovery took much longer than the millennial tempo of ecological succession, evidence for which can be found even in ancient sequences (Calder, 2006). Some have contributed the prolonged recovery time to the exceptional severity of the extinctions that occurred in the Late Permian, with key ecological components such as reefs (Pruss & Bottjer, 2004; Weidlich, 2007), being decimated. An alternative hypothesis has been proposed in which full recovery was prevented until the Middle Triassic by lingering or recurrent environmental hazards (Fraiser & Bottjer; 2007; Twitchett, 2007).

Organic carbon isotope anomalies that are coincident with the Late Permian and Middle Permian mass extinction events have been confirmed by the multiproxy study by the authors1 of non-marine strata from the Sydney Basin, southeastern Australia, of Permian and Triassic age (Retallack et al., 2006).  Mass extinctions were demonstrated by refined stratigraphic analysis to not be at the very end of the Late or Middle Permian, contrary claims by others (Clapham et al., 2009; Song et al, 2009), instead being before the upper boundaries of the Late Permian (Changhsingian) and Middle Permian (Capitanian) in China (Jin et al., 2000; Metcalfe et al., 2008;Wignall et al., 2009). Negative carbon isotope anomalies were found during the Early Triassic, as well s these marked perturbations of the carbon cycle, which contrasted with a Late Permian and Early Triassic that were isotopically quiet, as noted previously in marine records (Payne et al., 2004). Stomatal index studies by the authors1 of plant fossils from the Sydney Basin demonstrate that this episode of carbon isotopic volatility in the Early Triassic was also a time when atmospheric levels of CO2 were fluctuating. The times of these CO2 crises were times of higher levels of temperature and precipitation, as indicated by the chemical composition of palaeosols, which allowed lycopsids and large amphibians the take the opportunity to undertake transient migrations to the high latitudes of the Southern Hemisphere. The Early Triassic biota was maintained by successive greenhouse crises, and not merely an aftermath of the mass extinction event that was unusually severe.

 

Sources & Further reading

  1. Retallack, Gregory J., Nathan D. Sheldon, Paul F. Carr, Mark Fanning, Caitlyn A. Thompson, Megan L. Williams, Brian G. Jones, and Adrian Hutton. "Multiple Early Triassic Greenhouse Crises Impeded Recovery from Late Permian Mass Extinction." Palaeogeography, Palaeoclimatology, Palaeoecology 308, no. 12 (7/15/ 2011): 233-51.
Author: M. H. Monroe
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Last updated 07/05/2013
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading