Abstract: System tracl, a basic unit of T-gradc sequence, is a combinalion of the sarme-termm depositional systems controlled by water level changes (lacustrine level or sea level). Petroleum tends to being accumulated in the depositional sand bodies of differ-ent syslem tracts. The lype and distribution of lithologic pools could be predicted by characlerization of systeni tracts and analysis of depositional systems. In southwestern Qaidam basin, the characterization of system tracls shows that there exist developed transgressive system tract (TST) and various types of reservoirs 8uch as sand body of deltaic front, lacustrine beach and dam as. well as local turbidite of semideep lake. Based on synthetically geologic and seismic analyses, using digital seismic processing techniques (Jason's reservoir inversion, etc.), the sand body dislribution could be described, hence predicting that in southwest-ern Qaidam basin mainly developed the lithologic pools of SB, TU, DT and SS types.

Key words: sequence stratigraphy, nounmarine sediment, system tracl, reservoir: petroleum exploration, Qaidam