The accurate determination of geological age is a key to understanding the history and process of paleolake evolution and oil and gas exploration in continental lake basin.However,improving the accuracy of geological ...The accurate determination of geological age is a key to understanding the history and process of paleolake evolution and oil and gas exploration in continental lake basin.However,improving the accuracy of geological age has always been a difficult scientific problem.A 609-m-thick,continuous lacustrine mudstone and sandstone succession in Chezhen Sag(eastern China)provides an ideal middle Eocene sedimentary record for establishing a high-resolution stratigraphic chronology framework.Based on spectrum analysis and sliding window spectrum analysis of the natural gamma(GR)logging data of well Che 271(C271)in Chezhen Sag,the periods of 405 kyr and 40.1 kyr were filtered by a Gaussian bandpass filter,and a“floating”astrochronological time scale(ATS)was established.The total number of 405 kyr eccentricity cycles were 13.6 and 40.1 kyr obliquity cycles were 138 which recorded from the upper member 4(Es4U)to the member 3(Es3)of the Eocene Shahejie Formation,and the depositional duration was 5.53 Myr.Correlation Coefficient(COCO)analysis and evolutionary Correlation Coefficient(eCoCo)analysis found that the optimal sedimentary rate of different strata.Sedimentary noise simulation revealed the history of paleolake water changes in the Middle Eocene in the Chezhen Sag,according to which four sequences are divided.The study shows that the lake level change of Chezhen Sag in the middle Eocene shows prominent 1.2 Myr cycles and an antiphase well-coupled relationship with obliquity modulation.Finally,we propose a model to explain the relationship between the orbital cycle and lake level change in the continental lake basin.When the obliquity of the earth increases,the middle and high latitudes of the earth will be closer to the sun,the direct sunlight will be higher,and the meridional sunshine will increase,thus accelerating the evaporation process of lake basin water.When the seasonal changes are obvious(maximum period of 1.2 Myr ultra-long obliquity),this effect is more significant.The relative lake level change based on the restoration of high-precision ATS has significant scientific and economic value for understanding the vertical evolution of continental stratigraphic sequences and the formation and distribution of oil and gas resources.展开更多
The Chezhen Sag,located in the north-western Jiyang Depression,is one of the most important oil-bearing sags in the Bohai Bay Basin.Due to the low degree of exploration in the sag,paleosalinity and sedimentary environ...The Chezhen Sag,located in the north-western Jiyang Depression,is one of the most important oil-bearing sags in the Bohai Bay Basin.Due to the low degree of exploration in the sag,paleosalinity and sedimentary environment of the sag in the 3rd Member of Paleogene Shahejie Formation(Es3)is not clear.Recovering the paleosalinity and lake level fluctuations is helpful for understanding organic matter rich rocks sedimentation.Therefore,a detailed geochemical,mineralogical and paleontological analysis of the Es3 in the Chezhen Sag was conducted.Index like Sr/Ba ratios,B/Ga ratios,equivalent boron content and methods concluding Adams'formula and Couch's method were adopted to reveal the paleo-salinity and lake level variations.The results indicate that the lower submember(Lower Es3)was deposited in a salt water with high salinity,accompanied by dry climate and transgression event.The middle submember(Middle Es3)and upper submember(Upper Es3)record a freshwater to brackish environment.The paleosalinity and paleoclimate changes are consistent with the global sea level variations.The type and content of sporopollen indicate a dry climate in Lower Es3,which further confirms the reliability of the reconstruction results of paleosalinity.Combined with the paleoclimate and previous marine paleontological evidence,we proposed that the high salinity period is associated with a high lake level and a large-scale transgression event in Lower Es3.According to salinities and corresponding Lake depths,we established a sedimentary environment variation model of the Es3 Member in Chezhen Sag.展开更多
文摘The accurate determination of geological age is a key to understanding the history and process of paleolake evolution and oil and gas exploration in continental lake basin.However,improving the accuracy of geological age has always been a difficult scientific problem.A 609-m-thick,continuous lacustrine mudstone and sandstone succession in Chezhen Sag(eastern China)provides an ideal middle Eocene sedimentary record for establishing a high-resolution stratigraphic chronology framework.Based on spectrum analysis and sliding window spectrum analysis of the natural gamma(GR)logging data of well Che 271(C271)in Chezhen Sag,the periods of 405 kyr and 40.1 kyr were filtered by a Gaussian bandpass filter,and a“floating”astrochronological time scale(ATS)was established.The total number of 405 kyr eccentricity cycles were 13.6 and 40.1 kyr obliquity cycles were 138 which recorded from the upper member 4(Es4U)to the member 3(Es3)of the Eocene Shahejie Formation,and the depositional duration was 5.53 Myr.Correlation Coefficient(COCO)analysis and evolutionary Correlation Coefficient(eCoCo)analysis found that the optimal sedimentary rate of different strata.Sedimentary noise simulation revealed the history of paleolake water changes in the Middle Eocene in the Chezhen Sag,according to which four sequences are divided.The study shows that the lake level change of Chezhen Sag in the middle Eocene shows prominent 1.2 Myr cycles and an antiphase well-coupled relationship with obliquity modulation.Finally,we propose a model to explain the relationship between the orbital cycle and lake level change in the continental lake basin.When the obliquity of the earth increases,the middle and high latitudes of the earth will be closer to the sun,the direct sunlight will be higher,and the meridional sunshine will increase,thus accelerating the evaporation process of lake basin water.When the seasonal changes are obvious(maximum period of 1.2 Myr ultra-long obliquity),this effect is more significant.The relative lake level change based on the restoration of high-precision ATS has significant scientific and economic value for understanding the vertical evolution of continental stratigraphic sequences and the formation and distribution of oil and gas resources.
基金supported by the Sinopec Shengli Oilfield Cooperation Project named“Reunderstanding the sedimentary system of the third to the fourth member of the Shahejie Formation in the Chezhen Depression and the distribution of hidden traps”and China Postdoctoral Science Foundation(No.2021M700537).
文摘The Chezhen Sag,located in the north-western Jiyang Depression,is one of the most important oil-bearing sags in the Bohai Bay Basin.Due to the low degree of exploration in the sag,paleosalinity and sedimentary environment of the sag in the 3rd Member of Paleogene Shahejie Formation(Es3)is not clear.Recovering the paleosalinity and lake level fluctuations is helpful for understanding organic matter rich rocks sedimentation.Therefore,a detailed geochemical,mineralogical and paleontological analysis of the Es3 in the Chezhen Sag was conducted.Index like Sr/Ba ratios,B/Ga ratios,equivalent boron content and methods concluding Adams'formula and Couch's method were adopted to reveal the paleo-salinity and lake level variations.The results indicate that the lower submember(Lower Es3)was deposited in a salt water with high salinity,accompanied by dry climate and transgression event.The middle submember(Middle Es3)and upper submember(Upper Es3)record a freshwater to brackish environment.The paleosalinity and paleoclimate changes are consistent with the global sea level variations.The type and content of sporopollen indicate a dry climate in Lower Es3,which further confirms the reliability of the reconstruction results of paleosalinity.Combined with the paleoclimate and previous marine paleontological evidence,we proposed that the high salinity period is associated with a high lake level and a large-scale transgression event in Lower Es3.According to salinities and corresponding Lake depths,we established a sedimentary environment variation model of the Es3 Member in Chezhen Sag.
