ORGANIC FACIES ASSOCIATIONS IN RELATION TO SEDIMENTARY ENVIRONMENTS AND TECTONIC EVOLUTION IN THE YITONG GRABEN,NORTHEASTERN CHINA

Organic fades is defined in this paper as a mappable stratigraphic unit containing a specific genetic organic matter type in certain abundances. The three-dimensional morphology, paragenetic relationship and association pattern of genetically related organic facies types in a given chronostratic or lithostratic unit are referred to as the organic facies associatio(OFA). Four organic facies types namely Organic Facies B,C,D and E have been recognized in the Yitong Graben with the aid of combined sedimentological and organic geochemical studies. Although sedimentary environmental analysis indicates that the depositional fill features of different subunits in this graben are similar, the organic basin-fill sequences and organic facies associations of different subunits are quite different in various depressions. Organic facies and its association studies have remedied the defect of sedimentary environmental analysis which takes framework sandstones as its major object, and thus revealved the tectonic subsidence and depositional fill history of the basin more effectively.