Keywords: 
• sequence-tract /
• depositional systems /
• Mingyuefeng Formation /
• west Lishui sag /

Abstract: The Paleocene Mingyuefeng Formation, an important oil/gas bearing segment of the west Lishui sag, filled shallow sea and deltaic deposit which has formed an integrated third order sequence. The sequence boundaries show downlap, truncation and incised characteristic on seismic profiles. The incised valley shows blocky and trunk configuration on well logs. According to the initial and maximal transgression surfaces, the sequence may be classified into lowstand tract, transgression tract and highstand tract. According to the minor regression surface, there has been recognized the falling sea level system tract in the late highstand tract. Sequence boundary, major transgression surfaces and the minor regression surface have been confirmed by the enrichment and differences of paleobiology fossils. Through the sequence-tract mapping of the above 4 tracts, the distribution and evolution of depositional systems in different periods have been revealed. There developed incised valley, shoreline delta classtic and prodelta turbidite in lowstand and transgression tract. The incised valley and shoreline delta distributed on the western slope margin of the basin, and the depositional systems mainly came from the northwest and the southeast of the basin. The sparse prodelta turbidite distributed on the eastern abrupt margin of the basin and the depositional systems came from the east. It is charactered by large-scale progradation delta front sandstone in the highstand tract and falling sea level tract. The highstand tract delta distributed on the west margin of the basin, and there developed more on the south than on the north. The depositional area of the basin has obviously shrunk in the falling sea level tract so that the deltaic sandbody centralized on the central section of the western of the basin.