HYDROCARBON GEOCHEMICAL FIELDS AND ANOMALIES REGIONS IN THE NORTH YELLOW SEA BASIN

The North Yellow Sea Basin could be subdivided into three main depressions, i.e. the eastern depression, middle depression and western depression. According to the mean values and variation coefficients of the hydrocarbon gases,aromatic and condensed rings aromatic hydrocarbons of the seabed sediments, the geochemical fields of the three depressions are different. The geochemical field of the eastern depression is heavily heterogeneous for all indices, the field of the middle depression is the mixture of the homogeneous and heterogenous, and the western depression are characterised by slightly heterogeneous up to homogeneous anomalies. The geochemical anomalies of hydrocarbons are main distributed along the edge faults of the depressions and second sinks. It suggests that the geochemical fields and anomalies are controlled by faults, especially the edge faults of depressions. Integrating together all anomalies of hydrocarbons, eight geochemical regions (Ⅰ,Ⅱ,Ⅲ,Ⅳ,Ⅴ,Ⅵ,Ⅶ and Ⅷ) can be identified in the North Yellow Sea Basin. Among the eight, three(Ⅰ,Ⅱ, and Ⅲ)are in the eastern, three(Ⅳ,ⅤandⅥ) in the middle, and two(Ⅶ and Ⅷ) in the western depressions. Upon the integrated evaluation of geochemical anomalies, with reference to other geological factors, including structure, stratigraphy, source rock, reservoir, and cover, one first grade region(Ⅰ), three second grade regions(Ⅱ,Ⅲ and Ⅳ),and four third grade regions(Ⅴ,Ⅵ,Ⅶ and Ⅷ) are identified in the North Yellow Sea.