Study on the Origin of the Dolostone Intercalcated in the Black Shales in Middle Permian Lucaogou Formation Eastern Part of Southern Margin of Junggar Basin

The black shales and dolostones intercalcated with them had been researched petrologi-cally and geochemically of middle Permian Lucaogou Formation,eastern part of southern. Margin of Junggar Basin. The great similarity between them has been found. Based on the above study and the discussion of carbon and oxygen stable isotopie composition of the dolo-stone,it is concluded that: 1). Special thermodynamical and kinetic condition favorable for the formation of the environment where black shales were formed and organic evolution in then including: A): CO₃^2-,B):Low So₄^2-,C):High Mg²⁺/Ca²⁺ ratio and D) :organic-rich alkline and reducing environment. 2) The dolostones may had been precipitated in the evolution process of the environment where black shales were formed,and organic matter,accompaning with the increase of salinity and CO₃²- content of bottom water.