Before the uplifting in the late Ladinian age of the Indosinian

the Leikoupo Formation of the Middle Triassic in Sichuan Basin was an evaporite platform intermittently submerged by epicontinental sea.The overall paleogeographic pattern of the platform was high in the east and low in the west.The secondary uplifts and depressions developed in the platform acted as the basement for lagoon and salinized salt lake.The depocenter of the salt lake moved with the evolution of the paleogeographic pattern to areas along Chengdu and Nanchong in central and western Sichuan Basin during the deposition of the third and fourth members of the Formation.The Sichuan sea was uplifted as a whole due to the early Indosinian movement in late ladinian age

leading to the development of a wide-spreading paleo-weathering crust at the top of the Formation.In western Sichuan Basin

the crust is mainly located at the top of the fourth member.Exposed dissolution and deep burial dissolution led to the development of fractured-vuggy reservoirs within the crust.It is observed that the development of vuggy-fractured reservoirs is one of the major factors controlling hydrocarbon accumulation.A big breakthrough of gas exploration has been made with the well Chuanke-1 at the top of the Formation in the Xiaoquan structure of western Sichuan Basin.The analysis of the genesis of weathering crust and the main controlling factors for reservoir development shows that the top of the Formation is the potential exploration targets in western Sichuan Basin.