ANALYSIS ON THE OCCURRENCE FORMS OF SELENIUM AND INFLUENCING FACTORS IN LYUDAHUOFANG VERTICAL SECTION OF SONGNEN PLAIN

The Lyudahuofang section located in the east of Songnen Plain is a typical natural section for the study of selenium(Se) source in the Se-rich soil belt of Songnen Plain. A total of 33 samples are collected from two vertical sections of Cretaceous Nenjiang Formation (K₂n) to analyze Se and its seven occurrence forms, and physicochemical indexes such as TOC and pH. The results show that the Se content is 0.01×10^-6-3.05×10^-6, averagely 0.56×10^-6, with great variance in samples from different layers. Residual selenium is the main form in section samples with the average content of 0.092×10^-6, accounting for 51.98%. The Se content is mainly affected by parent material (oil shale). The correlation analysis results show that TOC and pH have certain effects on the distribution of Se content. That is, TOC is positively correlated with Se of strong organic bound, humic acid bound, ion-exchangeable and water soluble forms; while pH is negatively correlated with Se of all forms.