Crude oils in the block 1 and 3 in central Junggar basin have similar geochemical behaviors.The distribution of normal alkanes is complete and shows a single peak

with the main peak carbons ranging in C

17

～C

23

and weak pristane prevalence(the pristane/ phytane ratios ranging from 1.33 to 1.75).The characteristics of biomarkers are:(1) high contents of tricyclic terpane and gammacerane

(2) relatively high contents of pregnane

(3) "ascending" type homosterane distribution

(4) relatively high content of ααα20RC

27

sterane

and(5) high contents of β-and γ-carrotanes.The carbon isotope value is generally below-29‰.It is suggested

therefore

that the biological sources of crude oils would mainly be composed of low-grade aquatic organism and thallophyta

and the source rocks would have been deposited in lacustrine and reducing depositional environment.The crude oils are mainly generated from the Permian source rocks.Crude oils in the block 2 and 4 in central Junggar basin have also similar geochemical behaviors.The distribution of normal paraffin hydrocarbons is complete and shows a single peak

with the main peak carbons being C

13

and C

19

and strong pristane prevalence(the pristane/ phytane ratios ranging from 5.62 to 7.24).The characteristics of biomarkers are(1) very low content of tricyclic terpane

(2) relatively low content or absence of gammacerane

(3) low content of pregnane

(4) very high content of C

29

sterane

(5) a "reverse L"-shape homosteranes distribution

and(6) absence of β-and γ-carrotanes.The carbon isotope value is generally over-27‰.Therefore

the biological sources of the crude oils might be mainly composed of higher plants

and the source rocks would have been deposited in oxidizing environment.The crude oils are mainly generated from the Jurassic coal-measure source rocks.