Considerable quantity of oils and gas with diverse characteristics and origins has been discovered in the Tazhong-Ⅰ faulted slope break zone

Tarim basin.Totally 45 oil samples were gathered and analyzed with conventional geochemical approaches.The results show that the oils are characterized by significant predominance of light fractions and lack of heavy fractions

suggesting high thermal maturity of source rocks and/or thermal cracking of the oils.High absolute abundance of dibenzothiophene was detected in the oils

indicating a marine source.Several indexes(including relative distribution of gammacerane/C

30

hopane

C

27

-to C

29

-steranes

and C

30

-steranes) and biomarker fingerprints indicate that the oils in the area were generated from at least two kinds of primary source rocks.It was suggested that there is a strong gas invasion point at the eastern end of Tazhong-Ⅰ faulted slope break zone according to the abnormal distributions of diamondoid hydrocarbons and n-alkanes.There are evident differences among those oils even from closely adjacent wells

inferring different hydrocarbon generation and accumulation processes.All the features for the oil samples analyzed indicate the common characteristics of the oils in the superimposed basins in western China

i.e.

high thermal maturity

multiple sources and multiphase pooling

heterogeneity of chemical composition

and relative compartmentalization.This study is helpful for investigating the origin and accumulation mechanisms of the oils.It was suggested that great petroleum potential could be expected in the Tazhong-Ⅰ faulted slope break zone.