| The precise dating of Quaternary marine sediments plays an increasingly important role in the study of the paleoenvironment and paleoclimate.Optical Simulated Luminescence（OSL）dating determines the burial age of sediment since its last exposure to sunlight,and has advantages such as abundant dating materials and wide dating range,which have been widely applied to Quaternary sediment dating.Improving the accuracy and precision of OSL dating has been a research hotspot in the academic community.However,for a long time,more focus has been on testing procedures and calculation methods of equivalent dose,with relatively less research on environmental dose rate.Due to the complex sedimentary environment of marine sediments,large variations in sample properties,and the common occurrence of uranium series disequilibrium,accurate determination of environmental dose rate is particularly important in OSL dating of marine sediments.In this study,OSL dating was conducted on 46 samples collected from three different sedimentary environments:the coastal zone,shallow continental shelf,and deep ocean basin.This study analyzed the luminescence properties of all samples from the three different sedimentary environments through thermal luminescence experiments,preheat plateau experiments,and dose recovery experiments.Environmental dose rates of the samples were measured using three different methods,including HPGeγ-ray spectrometer,NAA,ICP-MS and AAS.Particularly,the study applied ultra-low background HPGeγ-ray spectrometer to analyze uranium series disequilibrium in marine sediments,aiming to improve the accuracy of OSL dating from the perspective of environmental dose rate measurement.The main findings of this study are as follows:1.This study confirms that the luminescence properties of marine sediments from the three different sedimentary environments were excellent,and the results of OSL dating were reliable.The thermal luminescence test results showed that all samples had a distinct 110°C thermal luminescence peak after 100s of regeneration dose.The preheat plateau experiments showed a stable plateau region in the equivalent dose with changing temperature.The dose recovery experiment showed that the ratio of measured dose to given dose was between 0.9-1,indicating that the optically sensitive traps in the quartz grains of the sample were highly sensitive to irradiation signals,and the SAR protocol is suitable for equivalent dose measurements.Equivalent dose results indicated that the samples had undergone sufficient exposure before burial,the distribution of De was concentrated,and the measurement results was reliable.2.HPGeγ-ray spectrometer,NAA,and ICP-MS（+AAS）showed some differences in U,Th,and K content results for the three types of sediment samples,and the reasons are:1)incomplete dissolution of U in heavy minerals during the ICP-MS pre-processing process;2)ICP-MS（+AAS）measurement results containing some non-radioactive isotopes;3)the use of samples in NAA is limited,and the dilution effect of non-radioactive substances in sediments has a significant impact on measurement results;4)there is an imbalance of uranium system in the sample.The results of comparative analysis indicate that NAA and ICP-MS（+AAS）were suitable for measuring terrestrial sediments with relatively homogeneous lithology,but not suitable for measuring marine sediments with commonly observed uranium series disequilibrium phenomenon,and ICP-MS was not suitable for measuring samples with high heavy mineral content.3.There is a common phenomenon of uranium-series disequilibrium in marine sediments,which requires measurement and analysis using HPGeγ-ray spectrometer.The ZBW borehole is located in a semi-enclosed sea area with low deep-water oxygen concentration and high organic content,resulting in autogenous uranium absorption phenomenon.This study used the measurement results of HPGeγ-ray spectrometer to calculate the content of autogenous uranium and corrected the environmental dose rate,the error before and after correction was 11%.Samples from the shallow section of U1514B borehole exhibited excess 226Ra and 210Pb contents far exceeding that of parent nuclide 238U,with 226Ra and 210Pb contents exponentially decreasing and becoming stable as depth increases.This study incorporated excess 226Ra and 210Pb contents into the calculation of environmental dose rate,thereby obtaining more reliable OSL dating results.Research shows that the HPGeγ-ray spectrometer can be used to determine whether a sample is in a radioactive equilibrium state and to analyze and correct uranium-series disequilibrium,making it an accurate and widely applicable method for measuring environmental dose rates in marine sediment luminescence dating studies. |
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