ABRUPTNESS OF THE MARINE END-PERMIAN EXTINCTION EVENT IN SOUTH CHINA EVIDENT IN LARGER DATA SETS WITH INCREASED RESOLVING POWER

The end-Permian mass extinction is recorded as an abrupt event in the ranges of marine taxa preserved in the Meishan section, South China (Jin et al., 2000). In order to overcome the possible shortcomings of single sections, we have extended the inventory to another 10 sections representing the Lower Yangtze, Upper Yangtze, and Dian-Qian-Gui basins from South China and 6 sections from Tibet, the Salt Range, and Kashmir to represent the Perigondwana region. Local taxon ranges have now been established for more than 1250 species (compared with 300 in the earlier study) including conodonts, brachiopods, foraminifers, fusulinoideans, ammonoids, bivalves, ostracodes, pollen and spores. The enlarged data set deals more effectively with stratigraphic incompleteness, facies control of preservation, and biogeographic differences between basins. The local range charts were combined using conodont ranges. Rather than group the data into conodont zones, however, we built an unbinned sequence of all the individual events by constrained optimization (CONOP). This process resembles a multi-dimensional graphic correlation. It uses heuristic searches (simulated annealing) to find sequences of events with the least misfit to all the field evidence. Isotopic ages of exceptionally high precision from 5 sections provide a test and calibration of the resulting composite section, which spans at least 6 million years. More than 10 of the dated events fall in the critical interval between 252 and 254 Ma. All the individual basins, the South China region, and the northern Perigondwana region reveal an abrupt extinction event. More than 2500 sequential estimates of taxon richness are possible in the composite section. Estimated richness drops sharply from more than 130 taxa to about 30 in a brief interval that appears to be shorter than 0.5 million years. Composite taxon richness at each estimate is found to be an approximately linear function of the number of stratigraphic sections that span the same moment in time, but the regression differs significantly between late Permian and early Triassic times. With or without correction for this effect, the increased resolving power does not reveal a stepped or phased extinction; the apparent abruptness of the end-Permian extinction survives very close inspection.