The biomarker compounds of the Bachu Formation mudstone and limestone collected from Qu-4 Well in Tarim Basin could be divided into two types:1.n-alkanes and isoprenoid alkanes;2.tricyclic terpane and pentacyclic terpane.Thermal simulation was made and the results suggest that

different simulation temperatures had different biomarker compound combinations.This was similar to that of the simulation made before.According to the oil-source comparison

the ratio of tricyclic terpane C

21

/C

23

in the crude oil generated from Carboniferous source rocks is usually greater than one

this differs distinctly from that in the crude oil generated from Cambrian-Ordovician source rocks(C

21

/C

23

<

1).It is suggested that the oil drilled in Qu-1 Well may be derived from Carboniferous mudstone.