Depositional models of the Permo-Carboniferous carbonate rocks and their significance in Yingen-Ejinaqi area，Inner Mongolia，China

On the basis of the origin of the pedestal on which the carbonate platforms were built, carbonate platforms in Yingen-Ejinaqi and their surrounding areas can be classified into four types, namely volcano-elevated carbonate platform(VEP), delta-elevated carbonate platform(DEP), coast-subsiding carbonate platform(CSP) and shelf-shoaling carbonate platform (SSP). All the carbonate platforms have different depositional models, which cause big differences in the strata morphology and interlayer lithology. Furthermore, this results form different assemblages of source rock, reservoir and seal. For the volcano-elevated carbonate formation, reservoirs for oil and gas consiste of volcanic rocks, pyroclastic rocks from the volcanic pedestal and within its formation, as well as interbeded limestone and sandy conglomerates; source rocks are composed of dark shelf mudstone above or at the lateral side of its formation, interbeded limestone and dark mudstone within the formation; while seal rocks are those shallow marine facies mudstone above the formation, all these make up a complicated lithologic trap for oil and gas with self-generation and accumulation. For the delta-elevated carbonate formation, reservoirs are mainly composed of pedestal sandy conglomerate of braided-delta/fan-delta origin and interbeded sandy conglomerates within its formation, source rocks come from those shallow marine facies dark mudstone above or on the lateral side of the formation and the interbeded dark mudstones, while seal rocks are dark mudstone above or on the lateral side of the formation, thus turns into a complicated lithologic trap for oil and gas with self-generation and accumulation. The formations of the coast-subsiding carbonate and the shelf-shoaling carbonate belong to simpler oil-and-gas lithologic trap with self-generation and accumulation, reservoir made probably of only limestone, the source rocks and the seal rocks are both composed of dark shelf mudstone.