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Local structure around arsenic atoms in K-T boundary clays was studied by As K-edge XAFS spectroscopy. The threshold Eq energy of As and the characterization of the white peak of XANES spectra agree well with the values of As(+5) minerals like ^(AsO^COH^KfeO and CaQi(AsO4)(OH) according to the comparison with several types of arsenic minerals. This indicates that arsenic is in a high oxidation state As(+5) and occupies the AsO4 fcetrahedral site of a mineral in K-T boundary clays.

Local structures around Fe and chemical shifts in X -ray absorption fine structure (XAFS) spectra were investigated for synthetic /Fetotal ratio in the system by the XAFS method would appear to be less than ±0.10, and higher reliability than this value would be acquired in the comparison of relative values at half -maximum positions.

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