Reconstruction and application of thermal history of old strata in superimposed basin:A case study on the Sinian-Cambrian in the central Sichuan paleo-uplift of the Sichuan Basin
Reconstruction of the thermal histories of old strata in superimposed basins has always been one of the difficulties in studying the thermal history of sedimentary basin,due to scarce sample of palethermometer scale,complex thermal history,and difficult effective characterization of thermal history by a single method.Taking the Sinian Dengying Formation and the Cambrian Canglangpu Formation in the central Sichuan paleo-uplift of the Sichuan Basin as examples,this paper explores an effective palethermometer scale combination and method system which can indicate the thermal history of ancient strata in a superimposed basin.It reconstructs the thermal history of the key layers of Sinian-Cambrian in the central Sichuan paleo-uplift by combining the traditional palethermometer scale with the palethermometer scale of low-temperature thermochronology with different closure temperatures.Then,the thermal evolution characteristics of the strata in different tectonic stages,the thermal effects of main tectonic-thermal events and the controlling effect of paleo-geothermal on the key process of hydrocarbon accumulation are analyzed,and the adaptability and application significance of different palethermometer scales in the reconstruction of thermal history of old strata in a superimposed basin are discussed.And the following research results are obtained.First,the Dengying Formation and the Canglangpu Formation in the Gaoshiti-Moxi area of central Sichuan paleo-uplift mainly experienced two heating stages and two cooling stages.During the two heating stages,the highest paleotemperature of the Dengying Formation was close to 240 ℃,and that of the Canglangpu Formation was about 200 ℃ in the Gaoshiti-Moxi area of central Sichuan paleo-uplift,where the Emei mantle plume did not have the decisive impact.Second,under the control of paleo-geothermal,the thermal evolution process of the Lower Cambrian source rocks in the Deyang-Anyue rift area,and the burial dissolution peak and hydrocarbon charging and accumulation process of the Dengying Formation reservoir in the Gaoshiti-Moxi area can be correlated,while compared with it,the thermal evolution of the Lower Cambrian source rocks in the east flank of the rift is hysteretic.Third,the deep-burial heating during the evolution of foreland basin is an important stage in the transformation of organic matter from high maturity to over maturity and the cracking of crude oil into gas.The tectonic uplifting during the late Yanshan to the Himalayan period may provide a driving force for natural gas charging in the last two stages.In conclusion,different types of palethermometer scales can indicate the thermal evolution processes and tectonic-thermal events of old strata in superimposed basins in different stages.To reconstruct the thermal history of old strata in a superimposed basin,it is suggested to combine multiple palethermometer scales with multiple strata on the basis of palethermometer scale data analysis,together with the numerical simulation results of stratigraphic burial history and basinal paleo-heat flow to constrain the thermal history path in the key period with multiple means.
Sichuan BasinCentral Sichuan paleo-upliftGaoshiti-Moxi areaSinian-CambrianSuperimposed basinThermal history simulationPalethermometer scale
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