Fatty acids(methyl ester)of dissoluble organic matter in Quaternary mudstone samples obtained from 540-1 490 m interval in Sebei area of Qaidam basin are analyzed through GC-MS.Even-odd predominance index of normal fatty acids varies greatly in 1 200-1 381 m interval.It is caused by various factors

of which the input of organic materials and bacterial action are dominant.In intervals of 796-810.8 m

1 188.24-1 210 m and 1 291.54-1 300.74 m

several biomarker indexes of fatty acids

such as content of fatty acids

even-odd predominance index and component dispersancy index

are at their valleys

as the major organic matters input in these intervals are of aquatic organism type

which are easy to be degraded by bacteria.All these indicate that source rocks dominated by indigenously sourced organic matter type have relatively high gas generating potential.Abundance of unsaturated acid and isomeric acid are discovered in 1 188.24-1 210 m interval

indicating that the geochemical environment and type of gas source rock in this interval are suitable for living and growth of bacteria.This specific fatty acid distribution might indicate high quality gas source rocks.