SEQUENCES,FLOW PROPERTIES AND THE SEDIMENTARY MODEL OF THE XIGAZE IN SOUTHERN XIZANG

The turbidite sequences are recognized in the sandy and muddy flysch of the Xigaze Group in Xizang, including the sedimentary sequences resulted from the mud-rich cohesive high-density turbidity current, sandy high-density turbidity current, low-density turbidity current and "contained" muddy high-density turbidity current proposed by Pickering and Hiseott (1986), of which the sedimentary sequences resulted from the low-density turbidity current are closely similar to the Bouma sequences. But there are significant differences between them in grain size, grain-size distribution, sequence thickness and facies associations.
The analysis of sedimentary facies sequences, palaeocurrent direction and provenance indicates that the submarine fan systems of monodireetional source are well developed on the southern flank of the Xigaze flyseh basin, while the composite deposits derived from bidirectional sources and resuited frommultiple flows are recognized on the northern flank of the flysch basin. Furthermore, the discovery of a special turbidite type-the "contained" muddy high-density turbidity current deposits attests to the conclusion that the sedimentary basin of the Xigaze flysch is a residual one.