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  • 1 Kanazawa University Division of Material Sciences, Graduate School for Natural Science and Technology Kakuma-machi 920-11 Kanazawa Japan
  • | 2 Kanazawa University Department of Chemistry, Faculty of Science Kakuma-machi 920-11 Kanazawa Japan
  • | 3 Institute of Geochemistry Academia Sinica 550002 Guiyang P.R. China
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Abstract  

Thirty samples from a limestone stratum across the Pemian-Triassic (P-Tr) boundary layer in China were analyzed for 30 elements by instrumental neutron activation analysis, wavelength dispersive X-ray fluorescence and ICP-MS, and also for mineral compositions with a powder X-ray diffractometer. The depth profile was found to indicate a sudden change of elemental and mineral compositions across the P-Tr boundary. Also the profile showed severa peaks in elemental concentrations in the lower Permian layered samples as well as in the overlying Triassic strata, which are associated with the change of mineral compositions. Elemental profiles were found to be classified into 4 groups and to give some insights in the geochemical records. Ir is far less abundant (0.1 ppt) compared with that of the K-T boundaries (10 ppb), and the Ir/Co ratio is outside the K-T and Cl chondrite trends. This change of elementary profile is suggestive of the internal causes rather than the external ones such as an asteroid impact for the mass extinction at the P-Tr boundary.