Abstract: Abstract:In order to find out the gas source of gas hydrates in Muli coal field of Qilian Mountain permafrost, fortyfour Jurassic samples were collected from drilling holes of QH1,QH2 and QH3 for geochemical analysis. On the basis of GCMS experiment and microscopical maceral identification of organic matters, the results show that the ranges of TOC and Ro of samples are 14%-166% and 071%~079%, respectively; mudstones TI is greater than 40, and coals TI is less than 0;the peak of normal alkanes appears in the first and the main peak of carbon distribution is C17-C19,while Pr/ Ph is generally greater than 11; tricyclic terpenes has the main peak with C19TT-C20TT, and C24Te has absolute advantage to C26TT; the distribution of C27-C28-C29 sterane series shows as a reverse “L”; C31 homohopane is an important component in hopane series and the content of C34-C35 homohopane is low, and G/C30H is low and mostly less than 02. The results reveal that the Jurassic source rocks stay in a mature stage;organic matters mainly belong to Ⅱ2-Ⅲ type, which are mainly from higher plants;the sedimentary environment belongs to swamp facies; the organic matter abundance is relatively high, indicating to be mediumgood source rocks.It can be drawn a conclusion that Jurassic source rocks in the study area are keeping in an oilgenerating stage and not the main gas source rocks.

Key words: source rock, maturity, abundance of organic matter, organic matter type, biomarker