Geochemical Characteristics of Jurassic Marine Source Rock in Amu Darya Basin and Comparison with Marine Source Rocks in China

Key words: 
• marine limestone /
• marine mudstone /
• resource rocks assessment charts /
• Amu Darya Basin

Abstract: Upper Jurassic marine source rocks in Amu Darya Basin are a set of generally accepted mature source rocks, and the maturity of them show difference against Paleozoic high-over maturity marine source rock in China. Through geochemical analyses of upper Jurassic rock samples in right bank of Amu Darya Basin and contrast among similar source rocks from basins of China Tarim, Huabei, Turpan-Hami, Bohai Gulf, we examine mature marine source rocks in Amu Darya Basin and build evaluation standard and charts of organic matter abundance and types. The results show that there are two types of Jurassic mature marine source rocks in Amu Darya Basin: limestone and mudstone, and the organic matter abundance of limestone is slightly higher than the Paleozoic limestone in Tarim Basin and middle-upper proterozoic limestone in North China Platform, and is close to the Permian limestone in Sichuan, while the organic carbon of mudstone is equal to that of Jurassic mudstone in coal-measures and is much better than the marine mudstone in Tarim Basin and North China Platform; marine mudstone belongs to type Ⅰ₂~Ⅱ source rock while marine limestone belongs to type Ⅲ~Ⅱ source rock. Comprehensive analyses show that ①upper Jurassic marine limestone belongs to middle class source rock while marine mudstone belongs to good source rock, and the TOC standard value is 0.5% and 3% respectively; ②parameters like resolvable chloroform asphalt “A” constituents, relation between Pr/Ph and Ph/nC₁₈、polycyclic aromatics "benzfhiore tri-fluorene" of marine carbonate rock or mudstone major in lower eukaryote not only discover the generation environment of source rocks, but also are good parameters to distinguish types of mother matter. The build of evaluation standard and charts of upper Jurassic marine mudstone and limestone in Amu Darya Basin have great significance on overseas marine basins hydrocarbon resources assessment.