PALEOGEOGRAPHY OF THE LATE PERMIAN – IMPLICATIONS FOR CLIMATE, GEOCHEMICAL CYCLES, AND MASS EXTINCTION

By the end of the Late Permian, most continents had collided to form the supercontinent of Pangea, a concept originally proposed by Alfred Wegener. The general geographic settings for this time are well-known, but the positions of Panthalassic mid-ocean ridges and of Tethian islands and seaways and their impact on the environment are uncertain. The geographic and tectonic changes at the Permian-Triassic boundary affected significantly the most severe mass extinction of species. One hypothesis for the extinction favors a climatic response to an increase in tectonic activity and associated large-scale volcanism, resulting in ocean stagnation and widespread anoxia with fatal consequences for marine and land organism. The concept is supported by recent interpretations of geochemical data suggesting that periodic upwelling of toxic hydrogen sulfide-rich water masses contributed to the extinction of species.

In this paper, we review the impact of mid-ocean ridges and sill depths on the Late-Permian climate and the implications for widespread anoxia and extinction. Comprehensive climate model results indicate that ridges promote diapycnal mixing along the ridge axis, but enhance inter-basin gradients of oxygen. Shallow passages between the Tethys and Panthalassa could have contributed to stagnation and low oxygen concentrations in the Tethian basin.

The climatic changes and tectonic activities at the end of the Permian, enhancing continental weathering and thus increasing nutrient input into the ocean, may have drastically changed marine productivity patterns and hence oxygen consumption in the deep sea.