Geochemical Characteristics and Genetic Mechanism of Permian Dolomitic Clastic Rocks in Northwestern Junggar Basin

Key words: 
• Junggar Basin /
• Permian /
• dolomitic clastic rocks /
• geochemical characteristics /
• genetic mechanism

Abstract: The types and lithology characters of Permian dolomitic clastic rocks in northwestern Junggar Basin are investigated by means of petrologic analysis, Xray indentification, carbon and oxygen isotope geochemistry and element geochemistry analysis, also analyzed Dolomization mechanism, Established dolomitization model. dolomitic clastic rocks in study areas include dolomitic mudstone, dolomitic siltstone, dolomitic tuffaceous siltstone, dolomitic tuffaceous shale,ect. And dolostones which are formed through dolomitization by replacing lacutrine plaster and siliceous (tuffaceous) components mainly consist of powderfine dolomites with automorphic or hypidiomorphic crystals, while residual calcite and late filled calcite cement commonly exist. The ratio of V/ Ni(1.2～4.8)content of Sr(95.5～782.2 μg/g)Mg/Ca(0.5～3.0),the degree of order(0.36~0.98)δ¹⁸O_PDB(14.8‰～3.2‰)and δ¹³C_PDB(1‰～5.2‰)all have larger variation range. The dolomitic rocks in this area mainly formed in a relatively weak hydrodynamic conditions, deep, peaceful, salt and lowsalt semiclosed terrestrial bay environment, have a characteristic of several stages and various causes. During Permian periods, in the researching zone the tectonics is complex, fault development, subtropical hot climate and frequent volcanic which provide favourable source of Mg²⁺ and permeability channel for the rich magnesium fluid fast flow. Comprehensive research show that these dolomitic rocks have three kinds of genetic types: Penecontemporaneous dolomitization, buried dolomitization, hydrothermal dolomitization.