Abstract:

During the Middle and Late Triassic，western Sichuan Province experienced a transform ing process from marine facies，transitional facies，to continental facies.Most source rocks and reservoir rocks developed during that period.Based on drilling and outcrop data and regional geological characteristics，this paper exam ines its lithoˉpaleogeographic features and evolution.During the deposition of the Leikoupo Formation to theMa’an-tang Formation，from west to east，the sedimentary environmentwas deepwater basin，platform margin and platˉform.The high energy platform edge shoal/reef facies and intraplatform shoal facies are favorable targets for petroleum exploration.During the deposition of the2 nd member and the3 rd member of the Xujiahe Formation，itwas a marineˉterrestrial transitional setting with delta deposits.Several m icrofacies，such as delta plain distributary channels，delta front subaqueous distributary channels and mouth bars，are favorable for the development of reservoirs.They have been the main exploration targets in recent years.The AnxianMovement，which occurred at the end ofdeposition of the3 rd member of the Xujiahe Formation，is a key point for the transition ofmarine facies to terrestrial facies in western Sichuan Province.At that time，the Longmen Mountain area was folded to mountains completely and the whole Sichuan Basin was turned into a continental sedimentary environment.During the deposition of the4 th member and the5 th member of the Xujiahe Formation，western Sichuan Provincewas dom inated by fluvial fans，lacustrine deltas and lake systems.By systematically exam ining theMiddle-Late Triassic litho-paleogeographic framework and evolution in western Sichuan Province，we can further check our exploˉration and appraisal approaches，analyze exploration strategies and figure outmain exploration targets，so as to guide exploration in future.

Key words: exploration target, significance for petroleum exploration, paleogeographic evolution, MiddleˉLate Triassic, western Sichuan Province