Beier sag is one of the prolific sags in Hailar Basin.However

the significance of high quality source rocks consisting of dark mudstone

marl

oil shale and calcareous mudstone

developed in the SQ2 sequence of the transgressive system tract in the sag

had been overlooked in previous studies.Based on various data including the measured TOC

content of the chloroform asphalt “A”

hydrocarbon generation potential(S

1

+S

2

)

vitrinite reflectance

as well as TOC from log interpretation

a detailed study of the source rocks was carried out in the context of sequence stratigraphic framework by using the geochemical-sequence analysis method to identify and evaluate the system tracts in which the major and quality source rocks had dwelled and calculate the amount of hydrocarbon generation and expulsion of the source rocks.The results show that most indexes including TOC

chloroform bitumen “A”

S

1

+S

2

and etc.

indicate that the source rocks in SQ2 and SQ3 are good to excellent in quality and dominated by oil-prone organic matter

meaning the two sequences are the major source rocks in the sag.The major source rocks are strongly heterogeneous and the high-quality source rocks were mainly developed in transgressive system tracts and early stage high stand system tracts(especially in SQ2).Calculation of hydrocarbon generation and expulsion from the source rocks shows that the source rocks in SQ2 contributed the most with hydrocarbon generation amount accounting up to 84% of the total and hydrocarbon expulsion amount accounting up to 93% of the total.The SQ2 was therefore considered the most promising home for source rocks in the sag.Evaluation of source rocks wiith geochemistry method can be used not only to guide exploration in brown blocks but also to improve working efficiency of source rock evaluation of green blocks with rare wells and samples.