STUDY ON TERRIGENOUS SEQUENCE STRATIGRAPHY FOR THE STEEP SLOPE OF FAULT-DEPRESSED LACUSTRINE BASIN-A CASE STUDY:THE UPPER MEMBER OF EH_3 IN THESHUANGHE-ZHAO' AO AREA,BIYANG FAULT-DEPRESSION
Hu Shouquan; Guo Wenping ;Liu Shugen; Tong Chongguang(Zhongshan University, Guangzhou 510275) (ChengduInstitute of Technology, Chengdu 610059)
in this paper, the upper member of Eh_3 in Shuanghe--Zhao'ao area of Biyang fault--depression is treated as a case to study terrigenous sequence stratigraphy and to establish a terrigenous sequence stratigraphy model for the steep slope of fault--depressed lacustrine basin. The terrigenous sequence stratigraphy model is composed of boundary model, system tract model, and terrigenous sequence stratigraphic model which includes lithologic framework model and chronostratigraphic framework model. The research shows that two kinds of terrigenous sequence (i. e. type Ⅰ and type Ⅱ ) can be recognized in the steep slope of fault--depressed lacustrine basin. A complete terrigenous sequence of type I can be divided into four system tracts: Lowstand System Tract (LST) ， Trangressive SystemTract (TST), Highstand System Tract (HST) and Regressive System Tract (RST) from bottom totop, and has five boundaries in which the top and bottom belong to sequence boundary, and other threeto system tract boundary. While terrigenous sequence of type Ⅱ lacks LST. The geometrical shape ofsedimentary body in every system tract appears wedge--like, namely sedimentary wedge, and the crossconfiguration of sedimentary factes in every system tract regularly change from basin--margin to basin-inside. The chronostratigraphic framework model clearly shows that sediment--filling history and distribution character in time and space for terrigenous sequence of the Upper Member of Eh_3 in research area.