Halahatang Sag has been one of the focuses for petroleum exploration in recent years.In order to confirm its oil source

depositional environment

thermal maturity and possible source rocks

systematic aromatic biomarkers analyses were performed on 26 oil samples from the Halahatang Sag and the Ordovician in Tahe oilfield as well as 4 potential source rock samples from the unmodified foreland region of the Tarim Basin.The results show that the Halahatang oil samples are characterized by high contents of naphthalenes and phenanthrenes

low content of biphenyl

low abundance of 1

2

5-TMN

high abundance of 1

3

6-TMN

high ratios of 4-MDBT/DBT and(2+3)-MDBT/DBT

and light carbon isotope of aromatics

which are similar to those of oil samples from the Tahe oilfield

indicating typical marine origin with contribution of lower algae and bacteria in predominance.High relative content of dibenzothiophene and low values of DBT/P and Pr/Phinfer a strong reducing depositional environment and carbonate lithology for the source rock.The equivalent vitrinite reflectances

i.e.Rc1 and Rc2

reveal a moderate to high maturity.Comparison of methyl triaromatic sterane isomeride shows that the Halahatang and Tahe oils correlate well with the Middle-Upper Ordovician source rocks

indicating a genetic affinity.