隠岐島後(島根県)の飯山珪藻土の元素組成(予報)

Diatomite is an important resources for the brick stones in the Oki-Dogo Islands，Southwest Japan．This report involves XRF analyses（major and trace elements）of the Miocene linoyama diatomite，and indicates briefly the major elements characteristics．
SiO_2 contents show a negative good correlation with most of the major elements（r^2 values range from 0.69 to 0.98）excluding MgO and P_2O_5．This suggests that dilution effects of biogenic silica are significant for the composition of the diatomites．On the SiO_2 vs Al_2O_3 diagram，other Miocene siliceous rocks of the examined area plot on the trend of the Iinoyama diatomite．Noteworthy is that Jodogaura samples of the nonmarine Tokibariyama Foemation have SiO_2 over 90 wt %，suggestive of chert formation due to the higher silica concentration of biogenic activity under lacustrine environments and/or diagenetic alteration．