Sequence Stratigraphy Study on the Cabroniferous Strata in Sichuan,Yunnan,Guizhou and Guangxi

The Carboniferous strata extensively distributes in Sichuan,Yunnan,Guizhou and Guangxi provinces. It has the characteristicse of clear stratigraphic division and correlation, plentiful sediment types and better outcrops. It is suitable to have the sequence stratigraphy research in these areas. This paper has focused on the accurate researches of the exposure sequence stratigraphy of the Carboniferous strata based on the detailed sedimentological study and accurate stratigraphic division and correlation of the Carboniferous strata in Sichuan,Yunnan,Guizhou and Guangxi provinces with the aid of the theory and studying means of the exposure sequence stratigraphy. Sequences are divided mainly by the characteristics of the key boundary surfaces,regional correlation,sedimentary facies sequence changes,parasequence stacking patterns,facies assemblage and sedimentary geochemistry. It has expounded in detail the outcrop signs of the sequence division and various boundary surfaces. The Carboniferous strata in the study area are divided into 10 third\|scale sequences, which are named from sequence 1 to 10, with the upper series of Carboniferous strata having 5 sequences and the lower series also. In the lower series of Carboniferous strata, Yanguan stage are composed of sequence 1 to 2, and Datang stage from sequences 3 to 5. In the upper series, Huashiban stage are composed of sequence 6 and Dala stage of sequence 7, and Maping stage from sequence 8 to 10. According to the features of the bottom boundary surface, 10 sequences are classified into two sorts of sequences, which are type Ⅰ sequence (S\-1,S\-3,S\-6,S\-9,S\-\{10\}) and type Ⅱ sequence(S\-2,S\-4,S\-5,S\-7,S\-8). The bottom boundary surfaces of type Ⅰ sequence all have clear signs including the strong paleokarst,the different thickness eluvial facies,the strata discontinutity,the immense changes of sedimentary patterns and traits,the regional revival of river,the disappearence and abrupt changes of organism evolution and the huge and sudden alternation of carbon,oxygen and strontium isotope values. On the other hand, the bottom boundary surfaces of type Ⅱ sequence are character ized by the transient exposure,the weak erosion and the lithoface texture transformation. So it is discerned more difficultly than the bottom boundary surface of type Ⅰ sequence. This paper also has expounded in detail the sedimentary features of the first transgressive surfaces and condensed sections of sequences in the different sedimentary environments and basins. It has summarized the sedimentary characteristics of the different system tracts in the different facies and basins. On the basis of these researches, this paper has probed the sequence correlation in the different sedimentary facies and basins from the ways of the sequence numbers,boundary surface traits and system tract structures and has founded the time\|space pattern diagram of the Carboniferous sequence strata in the study area.