ANALYTICAL RESULT OF TRACE ELEMENTS IN OSTRACOD SHELLAS INDICATORTO RECONSTRUCT PALAEOENVIRONMENT
介形类壳体无机成份的定量分析及其指相意义

Trace chemical elements of forty-six ostracod shells have been accurately measured by using SEM with electron probe. According to their living environments and geological age, the specimens Leguminocythereis sp., Neomonoceratina sp., Abrotocythere quadricornis, A. ovata, A. plegadis, Cyprinotus sp., Jlyocypris sp., I. caohaiensis, I, weiningensis, I. bradyi, I. subbiplicata, Leucocythere plena, Limnocythere (Xinanolimnocythere)tribulosa, Hungarocypris sp., and Notodromas sp., can be divided into four groups: living marine ostracod group, living nonmarine ostracod group, fossil marine ostracod group and fossil nonmarine ostracod group. The living ostracods were collected from the South China Sea, Bohai Sea, East Lake in Wuhan Cith, Caohai Lake in Guizhou Province and a pool near the Daqing City, Heilongjiang Province, while the fossil ostracods were from the Tertiary and Quaternary strata in Jiangsu and Guizhou Provinces. The result reveals that the ostracod shells contain 9 kinds of chemical elements, calcium(Ca), aluminium (Al), iron (Fe), magnesium (Mg), potassium (K), chlorine (Cl), sulpher (S), sodium (Nay and barium (Ba) in the order of their value of content from high to low, in which the calcium is the most abundant (32-34%) and the total amount of all other trace elements is less than 10%. It is found that there is an obvious difference between the ostracods living in the sea and those in the fresh-water in their chemical content of shells. This paper deals with the difference to deduce the palaeoenvironment of fossil ostracods where they once lived in. Based on the available data, it is considered that the value of Ca/Mg, the frequency and average value of trace elements in ostracod shells are very significant in the recons-tructionof palaeoenvironment. In general, Ca/Mg of the marine ostracod shells is below 60, while that of nonmarine ones is above 80. The value of Ca/Mg between 50-90 indicates that the ostracods probably lived in the oligohaline environment. Ca, Mg, Si and Al of the marine ostracod shells occurred in the frequency of 100%. On the contrary, all element of nonmarine ones but Ca occurred less than 50%. In addition, the average value of magnesium and potassium in marine ostracod shells is six or seven times higher than that in nonmarine ones, while the average value of calcium and chlorine is rather different, the former being much lower than the latter. The analytical result of chemical content of ostracod shells helps throw light on the cause of different colors on ostracod shells and the process of their formation. Therefore, as indicator, the analysis of chemical elements on ostracod shells is very important not only for palaeontologists but also for sedimentologists to reconstruct palaeoenvironment.