CALCULATION OF DENUDED STRATA THICKNESS BY FLUID INCLUSION DATA—A CASE STUDY OF THREE DEPRESSIONS IN THE EAST CHINA SEA BASIN

On the plotted graphs of formation temperature of fluid inclusions vs.burial depth,the point with distinct change of temperature corresponds to the erosion surface of unconformity.So,on the diagram of temperature (or pressure) vs.depth a straight line passing through the data points recording the temperature (or pressure) and the depth below the denudation surface can be constructed by the regression method.This line is then extended upward to the point with the coordinate defining the ancient surface temperature,and the corresponding depth is inferred as the ancient surface.The distance between the denudation surface and the ancient surface is the denuded strata thickness.It is essential that strata thickness is corrected by coefficient of compaction when fluid inclusions are trapped in shallow burial conditions.This method has been applied to calculate the denuded thickness of the Tertiary (E₁,E₂,E₃ and N₁) and the Cretaceous (K) strata in the three depressions of the East China Sea Basin.The results show that the burial depth of most Tertiary ( E₂,E₃) strata has just reached or fully entered the thresholds of main peak maturation periods of oil.In the future,the exploration work should be focused on searching for the favorable structural traps prior to the depositional break.For the strata of K,E₁ and N₁,however,the thermal evolution history prior to the depositional break is unknown while that after the depositional break is much clear.Therefore,attention should also be paid to the structures after the depositional break.