Abstract: By means of sequence stratigraphy, sedimentology and with comprehensive study of core section, cuttings, well-logging, seismic informations, fossils and geochemistry data the authors recognized three kinds of unconformities and classified the Paleogene into seven seismic sequences of third grade, vertical section of which is transgression, regression and aggradation respectively. Tectonic subsidence play dominant role in their geometric shapes, basin fillings, sequence evolution and sediment distribution in the Wushi Sag. Outline of the sequences are in shape of box-wedge or sheet-wedge and boundaries of sequences are varied from bilateral fault to monoclinal fault overlap, so that the sequences show distinct semigrabens which overlay in different ways. Seven sequences were formed in different stage of tectonic evolution. The sequence of SQ₁ formed in initial rift stage and deposited alluvial sequence. Sequences SQ₂-SQ₄ developed in intense rift stage and sediment lacustrine sequence. Sequences SQ₅-SQ₇ formed in late period of rift before thermal subsidence and deposit mere and delta sediment. The place adjacent to the synsedimentary fault is the subsidence center and depocenter; meanwhile, controlling fracture migrates in horizontal made subsidence and sedimentary center of the sag changed.

Key words: Wushi Sag, unconformity, sequence, geometric architectures, tectonic subsidence, sedimentary system