Diatom oxygen isotopes have been widely applied in quantitative reconstruction of the paleoclimate and paleoen...
LI Dong & HAN JingTai~* Key Laboratory of Cenozoic Geology and Environment,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029, China
Detailed magnetostratigraphic and rock magnetic investigations on L8-S12 of the Songjiadian loess section in the Sanmenxia area,southernmost margin of the Chinese Loess Plateau were conducted in this study.Matuyama/Brunhes (M/B) boundary occurred at the bottom of the loess unit L8.The top and bottom boundaries of the Jaramillo polarity subchron are found in the middle of L10 and the bottom of L12,respectively.Magnetic fabric of the loess layers maintains the original depositional features and the recorded remanent magnetization analysis indicates little post-deposition disturbance experienced.In late Matuyama chron,two anomalies of geomagnetic field have been detected in L9.Our data demonstrated that these recorded anomalies were less likely a result of remagnetization,but more possibly the signature of geomagnetic excursions occurred,named SJD1 and SJD2.It is calculated that the midpoint ages of SJD1 and SJD2 are 0.917 Ma and 0.875 Ma,respectively,and the time-interval between the two events approximates 12 ka.Chronologically,SJD1 is close to the Santa Rosa (0.922 Ma) and SJD2 corresponds to the Kamikatsura (0.886 Ma) excursions.In consistence with previous studies,the geomagnetic field was weakened during these events.
WANG DaoJingWANG YongChengHAN JingTaiDUAN MuGangSHAN JiaZengLIU TungSheng
Detailed magnetostratigraphic and rock magnetic investigations on L8-S12 of the Songjiadian loess section in t...
WANG DaoJing~(1*),WANG YongCheng~2,HAN JingTai~1,DUAN MuGang~3,SHAN JiaZeng~1 & LIU TungSheng~1 1 Key Laboratory ofCenozoic Geology and Environment,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China
Diatom oxygen isotopes have been widely applied in quantitative reconstruction of the paleoclimate and paleoenvironment,but have rarely been reported in China.In the present study,Lake Sihailongwan in Northeast China was selected for detailed investigation of oxygen isotopic fractionation between diatom frustules and lake water induced by growth temperature.This study involved a 2-year period of field monitoring of the lake water temperature at multiple depths and biweekly collections of traps for both sediment and water at shallow and bottom depths(7 and 49 m below the lake surface,respectively),diatom separation and purification of the trap sediments,and oxygen isotope measurement for diatom silica and lake water samples.The conditioned experiment conducted herein demonstrated that the laboratory device,methods and techniques used in this study were capable of generating reliable data for the typical oxygen isotope composition of diatom frustules.The data obtained revealed a prominent linear relationship between the oxygen isotope composition of the modern diatom and lake temperature during growth.The fractionation coefficient was about-0.185‰/°C-0.238‰/°C in the temperature range of 3.6-24°C,which is consistent with the observations from various aquatic environments and laboratory culture with different diatom taxa.These findings provide strong support for the dominant control of the growth temperature on the oxygen isotope fractionation between the diatom frustules and ambient water.A notable difference in the fractionation coefficient was observed between the surface and bottom diatom oxygen isotopes,suggesting that various depositional processes and taphonomic effects influenced the surface and bottom trap samples.Another factor leading to this difference may be that enrichment by evaporation and dilution by rainfall have a stronger influence on the surface.Overall,the results presented here demonstrate significant progress in evaluation of diatom oxygen isotopes in China and draw attention to the di
