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The cause of the great Permian-Triassic (P-T) boundary mass extinctions remains unknown. A crucial step in identifying the cause involves a precise timing of the mass extinction interval (MEI) in order to reconstruct the pattern of biotic evolution and the chronologic record of potential triggers. Here we present an estimate of the P-T boundary MEI duration based on astronomical tuning of multiple cyclic sedimentary records. Magnetic susceptibility data from Shangsi, southern China, provide evidence for strong 405 k.y. orbital eccentricity forcing throughout the P-T boundary interval. Radioisotope dating combined with 405 k.y. tuning provides an absolute time scale through the P-T boundary interval at unprecedented high resolution. An estimated ~700 k.y. duration for the MEI at Shangsi is supported by eccentricity tuned estimates of four other sections in China and Austria. In addition, at Shangsi, the onset of mass extinction occurred shortly following a coincidence of minima in the observed ~1.5 m.y., 405 k.y., and ~100 k.y. cycles. A change in the magnetic susceptibility response to astronomical forcing occurred just prior to the onset of extinction, with reduced 100-k.y.-scale cyclicity continuing into the Early Triassic for more than 2 m.y. [ABSTRACT FROM AUTHOR]

The authors discuss the comments made by M. R. Rampino and K. Kaiho on their paper regarding the astronomical correlation of the Permian-Triassic (P-Tr) boundary interval. The authors say that Rampino and Kaiho questioned their definition of mass extinction interval (MEI) for the P-Tr boundary interval. They mention that their definition on MEI considers the aftermath and following extinctions through P-Tr boundary. Moreover, the interval of Permian fossils is discussed.

The end-Permian mass extinction, the largest biological crisis in Earth history, is currently understood in the context of Siberian Traps volcanism introducing large quantities of green- house gases to the atmosphere, culminating in the Early Triassic hothouse. In our study, the late Permian and Early Triassic atmospheric CO2 history was reconstructed by applying the paleosol pCO2 barometer. Atmospheric pCO2 shows an approximate 4x increase from mean concentrations of 412-919 ppmv in the late Permian (Changhsingian) to maximum levels between 2181 and 2610 ppmv in the Early Triassic (late Griesbachian). Mean CO2 estimates for the later Early Triassic are between 1261-1936 ppmv (Dienerian) and 1063-1757 ppmv (Spathian). Significantly lower concentrations ranging from 343 to 634 ppmv are reconstructed for the latest Early to Middle Triassic (Anisian). The 5 m.y. episode of elevated pCO2 suggests that negative feedback mechanisms such as silicate weathering were not effective enough to reduce atmospheric pCO2 to precrisis levels and that marine authigenic clay formation (i.e., reverse weathering) may have been an important component of the global carbon cycle keeping atmospheric pCO2 at elevated levels. [ABSTRACT FROM AUTHOR]