A HIGH RESOLUTION CHRONOSTRATIGRAPHIC FRAMEWORK FOR THE PERMIAN-TRIASSIC TRANSTION

The Permian-Triassic transition is distinguished by major events in biotic extinction, volcanic eruption, seawater chemistry, and by strong provincialism and slow biotic recovery. However, the interval and events are poorly constrained in a chronostratigraphic framework. A 20-myr time slice from the late Guadalupian (Middle Permian) to the early Olenekian (Early Triassic) is being examined, integrating marine and terrestrial paleontology and stratigraphy with radiometric ages, geochemical excursions and magnetic reversals. Establishment of GSSP's for the bases of the Changhsingian (latest Permian) and the Triassic at Meishan, China has helped define some of our terms, but radiometric ages through the interval are conflicting and the distribution and correlation of the major marine fossil group, conodonts, is at best controversial. A comprehensive taxonomic dictionary, dynamic synonymy, and species designation evaluation tool were developed to better understand conodont distributions and then applied to other fossil groups (particularly, radiolarians). Development of simple tools for stratigraphic compilation and application of correlation tools (graphic correlation, constrained optimization) were utilized to develop the refined framework. Radiometric ages, through the efforts of EarthTime, are becoming consistent. The magnetic reversals were inconsistent and needed to be recast as events in the chronostratigraphic framework to be built into a coherent stratigraphy. This was critical for marine-continental correlation. Results and progress can be monitored through the CHRONOS and PaleoStrat websites (http://www.chronos.org, www.paleostrat.org). The refined framework allows much better correlation throughout the marine realm and indicates the major extinction event in China was abrupt and isochronous at 252.6 Ma and the base of the Triassic is 252.5 Ma. A conodont, Hindeodus changxingensis, has a narrow range through this boundary interval from extinction into the earliest Triassic and is found throughout the Tethys.