埋藏后生作用对生物壳体87Sr/86Sr的影响研究

根据小渡口剖面２８层有孔虫、介形虫、腹足类生物壳体的微观观察、微量元素及其比值、＾８７Ｓｒ／＾８６Ｓｒ与微量元素特征对比经及水－岩反应＾８７Ｓｒ／＾８６Ｓｒ的混合模式，显示生物壳体遭受了埋藏后生作用，但对生物壳体原始的＾８７Ｓｒ／＾８６Ｓｒ比值基本没有改变或影响甚微，推测参与埋藏后生作用的流体与生物壳体具有相近的Ｓｒ同位素组成或较悬殊的Ｓｒ含量。同时，实际研究表明评价和判别埋藏后生作用对生物壳体原

THE EFFECT OF DIAGENESIS ON 87Sr/86Sr RATIOS IN ORGANIC SHELLS

The subtle difference in texture detected by SEM and trace element concentrations of the fossil samples of foraminifera, ostracode, gastropod from the 28th bed of the Xiaodukou profile in Nihewan, Hebei, shows that some modifications of organic shells result from diagenetic alteration. However, the model of water\|rock interaction implies that the modification of strontium isotope is dependent on the differences in strontium contents and \{\}\ \{87\}Sr/\ \{86\}Sr ratios between fluids and organic shells during water\|rock interaction. The diagrams of Sr\|Mn, \{\}\ \{87\}Sr/\ \{86\}Sr\|Sr, \{\}\ \{87\}Sr/\ \{86\}Sr\|Mn, \{\}\ \{87\}Sr/\ \{86\}Sr\|1/Sr indicate that the Xiaodukou fossil shells record the original \{\}\ \{87\}Sr/\ \{86\}Sr ratios. Meanwhile, some criteria with shortcomings are not always the reliable indicators. The \{\}\ \{87\}Sr/\ \{86\}Sr ratios of shells compared with textural and other geochemical methods may be a sound criteria to evaluate the effect of diagenetic alteration on \{\}\ \{87\}Sr/\ \{86\}Sr ratios in organic shells.