Multiple Organic Carbon Isotope Reversals across the Permo-Triassic Boundary of Terrestrial Gondwana Sequences: Clues to Extinction Patterns and Delayed Ecosystem Recovery

摘要

Organic materials across the palynologically defined Permian-Triassic (P-T) boundary from five major terrestrial basins in the interior of the former Gondwana Supercontinent show large to very large (5per thousand-15per thousand) multiple negative spikes of #delta#~(13)C, separated in places by sharp reversals of up to 20per thousand. Large oscillations of #delta#~(13)C_(org) between -36per thousand and -15per thousand from mean values of approx24 +- 2 in India, approx26 +- 2 in Madagascar, and approx23 +- 2 in South Africa occur before and after the P-T transition. The mean values are within the range of modern C3 plants (approx-25per thousand). The negative #delta#~(13)C_(org) spikes of the terrestrial plant remains complement similar spikes of smaller amplitude recorded globally in marine carbonates across the P-T boundary. Sensitivity analyses of carbon fluxes in a coupled atmosphere-ocean system indicate that the sharp declines in terrestrial and marine #delta#~(13)C can be explained by episodic release of methane from clathrates (approx-60per thousand) either directly into the atmosphere or via the oceans, possibly during the disintegration of the southern continental shelf of Tethys. The rapid increases in #delta#~(13)C may either signal aborted attempts of C4 plants (approx-13per thousand) to establish themselves at the expense of C3 plants or, more likely, reflect a punctuated increase in C3 biomass production related to elevated atmospheric CO_2. Detection of a gradual negative trend in the Upper Permian and a similar positive recovery in the Lower Triassic, separated by up to three large negative #delta#~(13)C spikes across the P-T boundary in at least four terrestrial sections, caution against models of the end-Paleozoic biodiversity collapse and ensuing Mesozoic recovery based on a singular perturbation at the P-T boundary. Rather, these transitions may reflect multiple ecosystem stability states and abrupt responses during gradual forcing of a complex nonlinear system with thresholds.