the Lower Assemblage refers to the whole thick pre-Mesozoic formations from Sinian system to Paleozoic Carboniferous system in Sichuan Basin. Three types of karst reservoirs develop in Sinian-Ordovician Carbonate rock in the Low Assemblage, which are tectonic unconformity karst, penecontemporaneous hiatus karst and contemporaneous karst reservoirs. Having been affected by long-term regional tectonic uplifts and frequent sea level eustasies, several regional tectonic unconformities, including ?1/Z2dy, O1/?2-3, S1l/O2b and P1/Z unconformities, and sequence boundaries formed and several contemporaneous shoal facies karst reservoirs developed under these unconformities. Superimposition and repeated reformation of multi-genetic karstification from early to late is the reason why carbonate karst reservoirs widely develop in horizontal and vertical extents in the Lower Assemblage.