SEDIMENTARY ENVIRONMENT AND GEOCHEMICAL CHARACTERISTICS OF HYDROCARBON SOURCE ROCKS IN THE CAMBRIAN BASE OF THE HEFEI BASIN

More and more attention is being paid to the marine hydrocarbon exploration in the Hefei Basin. The marime argillaceous source rock found in the Lower Cambrian base of the West Hefei Basin has important practical significance, and the stuey on its sedimentary environment and geochemical characteristics is the basis for the further hydrocarbon exploration. Sequence stratigraphical and orgnic geochemical study shows that its sedimentary tectonic environment is at the transitional stage of extensional depressing to shifting spreading, and the basin belongs to the transitional type of internal rift basins to passive continental marginal basins. The is very much advantageous to the formation and preservation of hydrocarbon source rocks. This set of source rocks has the average organic carbon content of 6.46% and I-typed organic matter, and its maturity characterized by R_o(2%-3.5%) and T_max (500-600℃) reflects its entering into the overmatured early or late stage, The biomarkers reveal that this set of source rocks was formed in the strong-reduction and high-salinity environment, and it originated from bacteria and algae these kinds of low-grade organism, and is in the evolutionary degree of the oil-generating stage. The maturity difference reflected from the two kinds of organic geochemical indexes may result from different organic matter they represent respectively, R_o and T_max mainly reflect the host rock maturity of source rocks, while biomarkers may mainly reflect the organic matter maturity of rock enclusure. The comprehensive study suggests that this set of source rocks not only is in the peak period of gas generation but also has the potential to form oil. The sedimentary environmental and geochemical research of this set of source rocks provides theoretical basis for the Lower Paleozoic natural gas pool prospecting in the Hefei Basin.