GCMS are used to analyse saturated hydrocarbon fractions of 17 argillite rock extracts of Dongtai depression so as to study the sedimentary environment

the type of organic matters and the maturity of early Tertiary source rocks with the aid of biomarkers such as sterane and terpane.Both OEP and isopre-noid distrt bution have proved that Ef

2

and Ef

4

are deposits under strong reducing environment in which gamma ceranes have emerged.Based on the ratio of sterane of different carbon number and that between sterane and terpane

sapropelicorganic matter(type Ⅰ and Ⅱ of kerogen)is found to distribute in regions where C

27

sterane exceeds 30% and where the ratio between C

27

sterane and C

30

hopaneplus mortane exceeds 0.5.On the basis of the epimerization of sterane and terpane

it can be deduced that the depth of the threshold of oil generationis about 2

100m.