Through gas chromatographic-mass spectrometric(GC-MS) analyses

11 series and 164 aromatic hydrocarbons

including naphthalene

phenanthrene

chrysene

biphenyl

fluorene

dibenzofuran

dibenzothiophene

triaromatic steroid

etc.

have been detected in oil sampled from Heidimiao

Saertu

Putaohua

Gaotaizi and Fuyu oil layers in Songliao Basin.Crude oil in Heidimiao and Saertu layers are mainly composed of triaromatic sterides and compounds of phenanthrene family.Crude oil in Putaohua layer are mainly composed of compounds of phenanthrene and chrysene families.Crude oil in Gaotaizi and Fuyu layers are mainly composed of compounds of phenanthrene and chrysene families and triaromatic sterides.All the break-points in vertical distributions of compounds of phenanthrene and chrysene families and triaromatic sterides appear at Putaohua layer

i.e.from the shallower Heidimiao layer to the deeper Fuyu layer

the contents of phenanthrene and chrysene families are tending to increase

while that of triaromatic sterides are tending to decrease.According to the content of triaromatic steroid and the combination of triaromatic sterides/phenanthrene family and dimethylphenanthrene/triaromatic steroid

crude oil in Songliao basin can be divided into three types

including the high triaromatic sterides crude oil in Heidimiao and Saertu layers

the low triaromatic sterides crude oil in Gaotaizi and Fuyu layers and trace triaromatic sterides crude oil in Putaohua layer.Based on crude oil in Songliao basin containing triaromatic sterides and the dibenzothiophene/phenanthrene being very low

it is believed that the source rocks in Songliao basin would have been deposited in weak oxidizing environment in freshwater-brackish lake.