Abstract: Many isolated mantle heat sources(or thermal plumes) in South China were produced beneath the crust during Mesozoic area,offering great influences on Mesozoic geothermal field in the area.Thermal evolution and maturity of organic matter,migation and preservation of oil and gas were in close ralationship with paleo-geathecvmal field,when taking consideration of ail and gas prospects of marine carbonates,not cnly the geachemical features of oil and gas genexation,but also their preservation conditions needs to be studied.The upper crust should preferably suffer less displacement and the covering sediments should be less affected by the mantle heat sources.Exposure of petrolcum bearing formatios to temperatures higher than 250℃ would be very harmful to its preservation.Because of the non-homogeneity of Mesozoic geotherenal field,the preservation situations of Palaeozoic hydrocarbons are different from place to place.Presumably,it is better to the west of Mt.luefeng in Hunan province then to the east.