PERMIAN CLIMATES: NEW DATA/MODEL RESULTS, AND INSIGHTS ON TERRESTRIAL VEGETATION CHANGES ACROSS THE PERMO-TRIASSIC BOUNDARY

The Permian is characterized by a Pangean world geography with ca 15 degrees northward motion of the major continents through this period, and a transition from icehouse to hothouse conditions that cannot be explained solely by such latitudinal motion. We analyzed fossil plant and lithological data to derive biomes (‘climate zones’) for two Permian stages, the Sakmarian (286 - 280 Ma) and Wordian (267 - 264 Ma). These represent remnant icehouse and transition toward hothouse world conditions. The results from our data are compared with those from GCM simulations for a range of prescribed CO2 levels and orbital configurations. CO2 level is an important factor (4x and 8xCO2 producing a better match with the data than 1xCO2). The effects of orbital variations are minor. However, even these elevated CO2 levels fail to match the data in the high southern latitudes. We discuss possible reasons for this data and model discrepancy in terms of oceanic heat transport.

Our approach to determining Permian climates also provides a framework for understanding changes in terrestrial vegetation across the Permo-Triassic boundary. These observed changes are usually assumed to have been synchronous and due to a global extinction. However, separate factors could have affected floras in different parts of the world and these could have operated within the limits of temporal resolution. Three main regions, Angara, Gondwana and China, have Late Permian plant remains. There is good evidence that the changes in Angaran vegetation occurred at about the beginning of Siberian flood basalt volcanism. Changes in the Gondwanan records could be largely attributed to disappearance of moisture sources and the consequent drying out of this region. The Chinese records can be ascribed to northward latitudinal motion of the North and South China blocks, these areas migrating out of the tropical everwet biome into progressively drier regimes.