Tertiary Qianjiang formation is rich in gypsum and salt.The content of chlorine ions in argillites is 0.1—1.5%

the average content of organic carbon and hydrocarbon is 0.61%

996 ppm respectively.The kerogen in Qianjiang formation is of mixed type with a higher genetic potential for petroleum.The normal-paraffins of source rocks from Qianjiang formation mostly fall in the C

22

-C

34

and show a distinct even-odd predominance with EOP values from1 to 1 approximately.During the deposition of this formation

in part of the fringing areas where the sedimentary layers have relatively nor-mal water salinity

the normal-paraffins also show a odd-even predominance with OEP values from1 to 1 approximately.These two predominance corres-pond to each other

but the former is the major one.Therefore

the authors consider that the even-odd predominance is the main path of the hydrocar-bon evolution in source rocks of salt lake facies.Among the isoprenoid alka

nes in source rocks of Qianjiang formation

phytanes are predominant with pristane-phytane ratios(pr/ph)1.Because of the well developed gypsum and salt and the lower geothermal gradient(2.3—3.0℃/100m)in the Jianghan basin

the evolution rate is slower and the buried depth is deeper than that of the organic matters in common continental source rocks.In Qianjiang formation

the petroleum generation threshold is about 2000m

mature threshold 2800m

petroleum genera-tion peak 3700m and the lower limit of liquid petroleum generation 4600m.Therefore the thickness of liquid window of hydrocarbon can be up to 2600m.The crude oil in Qianjiang formation can be classified into low-matured oil and matured oil.Its maturity is basically coincident with the maturity of source rocks

which reflects its features of close to oil source

short-distance migration

and which shows oil is generated from and reservoired in Qianjiang formation itself.