Abstract: Because the depositional shoreline break is difficult to recognize in the steep slope zone of fault-depressed lacustrine basin, it has been put forward that the location of specific wells is taken as reference to divide terrigenous sequence and system tract.A complete terrigenous sequence can be divided into 4 system tracts and has 5 boundaries, of which the top and the bottom belong to sequence boundary, and other 3 to system tract boundary.Low stand System Tract(LST)which bottom is a sequence boundary of type Ⅰ and top is first flooding surface formed during the period from the descent inflexion point(F)to the lowest point(L)of lacustrine level change.Trans gressive Systems Tract(TST)which bottom is a first flooding surface and top is marked by the emergence of condensed section formed during the period from the lowest point(L)to the ascent inflexion point(R)of lacustrine level change.High stand Systems Tract(HST)which bottom is marked by the emergence of condensed section and top is a maximal flooding surface formed during the period from the ascent inflexion point(R)to the highest point(H)of lacustrine level change.And Regressive Systems Tract(RST)which bottom is a maximal flooding surface and top is a sequence boundary of type I or type Ⅱ formed during the period from the highest point(H)to the descent inflexion point(F)of lacustrine level change.

Key words: Nanxiang Basin, Biyang sag, Continental facies, Stratigraphy sequence, Boundary, Model