Three acid series

including straight chain monoacid

straight chain binary acid and aromatic acid

have been detected in the kerogen of low mature Tertiary source rocks with low organic carbon content in Qaidam basin.Relative abundance of straight chain monoacid is the highest among these three acid series

and C

16:0

acid occurs as the main peak(saturated fatty acid)

with obvious even carbon number predominance.The volume of kerogen fatty acid is over three times that of enhanced kerogen fatty acid

and the former has much larger relative abundance of straight chain binary acid than the latter.In addition

the volume of fatty acid that enrich in carbonate crystals of source rocks in the form of calcium(magnesium)fatty acid salt and fatty acid is far greater than that occur in kerogen network.When these carbonate crystals were decomposed at high temperature(and at complex geologic conditions)

the fatty acid salt and fatty acid might be cracked into small molecular hydrocarbon

i.e.

gaseous hydrocarbon.The sulfur in deposited organic matters in the study area occur as pentabasic

hexabasic and octatomic ring stable states

and would make contribution to the enrichment and existence of fatty acid(salt)due to its strong electron negativity.