Evolution and hydrocarbon potential of the marine strata on the southeastern margin of the North China plate

The combustible gas and burned tunnels founded in the Dabie orogenic belt are concentrated to the North Dabie complex zone south of the Mozitan-Xiaotian fault and the Early Carboniferous metamorphosed quartz schist close to the Xinyang-Shucheng fault.The two faults have provided gas source pathways which are connected to deeper reservoir rocks.The Lower Cambrian Fengtai Formation below thrust nappes and the North Huaiyang Carboniferous strata,both of which occur as the marine source rocks,are considered as the main gas source rocks of the tunnel combustible gas.The Lower Cambrian Fengtai Formation consists of the continental marginal deposits,in which the marine muddy source rocks have been in an oversaturation stage of thermal evolution characterized by high carbon,high R_o,high T_max and lower chloroform-bitumen "A".The North Huaiyan Carboniferous source rocks have high abundances of organic matter with the III-type kerogen and high thermal maturation,resulting in the generation of abundant hydrocarbons.The discovery of the tunnel combustible gas indicates that the deep-seated marine strata in the Hefei Basin may be highly prospective for oil and gas resources.The future exploration should be carried out from the Mesozoic and Cenozoic basin systems to the deep-seated marine strata,with the emphasis on the "Palaeozoic source rocks and Palaeozoic reservoir rocks" or "Palaeozoic source rocks and Cenozoic reservoir rocks".