ORGANIC MATTER AND PYRITE BURIAL AND O2 AND CO2 FOR THE LATE PERMIAN AND EARLY TRIASSIC

The results of a theoretical isotope mass balance model are presented for the time dependence of atmospheric O2 and CO2 across the Permo-Triassic boundary. Averaged data for oceanic d13C and d34S were inputted each million year from 270 to 240 Ma. Results show a large drop in the rate of global organic matter burial during the Late Permian and a predominance of highly variable burial during the Early-to-Middle Triassic. Accompanying the drop in organic matter deposition was an increase in the burial of sedimentary pyrite, and a dramatic increase in the calculated global mean ratio of pyrite-S to organic-C. High S/C values resulted from an increase of deposition in marine euxinic basins combined with a decrease in the burial of low-pyrite associated terrestrial organic matter. This prediction of increased oceanic anoxia during the Late Permian and Early Triassic agrees with independent studies of the composition of sedimentary rocks

Weathering plus burial fluxes were used to calculate changes in atmospheric oxygen and carbon dioxide. The striking result is a continuous drop in O2 concentration from about 30% to 13% over a twenty million year period and a rise of CO2 to very high values at the P/Tr boundary with additional maxima during the early Triassic. The large changes in CO2 were obtained even while assuming no variation in volcanic CO2 input. These results are believed to have been due primarily to variations in land plant productivity leading to variations in global organic matter burial.