Chronology Of Last Glacial Maximum Sediments In The Coast Of Fujian, South China And Its Palaeoenvironment Significance

The coast in South China is an important area for the coupling of terrestrial,marine,and atmospheric processes.Widespread loose sediments in the area likely recorded regional climatic and geomorphic processes since the Late Pleistocene,and these can be deciphered through geochronology.Date the optically stimulated luminescence（OSL）and the AMS¹⁴C methods are commonly used to establish chronological frameworks of the Late Pleistocene and the Holocene.In the present study,comprehensive OSL and AMS¹⁴C dating are expected to provide a reliable age framework for the complex coastal sedimentary environments in South China.Eighteen samples prepared from the FN1 core retrieved from the Funing Bay in the coast of Fujian were used for dating using the OSL method.The single aliquot regenerative-dose（SAR）approach was employed for dating three grain-size fractions of quartz,while coarse-grained K-feldspars were used for post-infrared infrared stimulated luminescence（p IRIR）dating of the core.Seven samples from the core were also dated using the AMS¹⁴C technique.The results reveal the following:1)Minerals and grain size variations directly affect the accuracy of the luminescence dating.The present study demonstrates that cross-validation of the OSL dating data is an effective way to enhance their reliability.In the study of shelf and coastal paleoenvironment,it is necessary to combine OSL dating technology with AMS¹⁴C dating method to provide an accurate chronological framework.2)Ages obtained from the OSL,p IRIR,and AMS¹⁴C dating of samples from the FN1 core display some inconsistencies.Dating results from the three grain-size fractions of quartz from the upper section of the core are consistent within the error range,and these agree with ages from the AMS¹⁴C method for the corresponding horizon.This consistency demonstrated that the samples utilized were fully bleached and the ages obtained from the OSL method using quartz grains are reliable.However,OSL ages based on the three grain-size fractions of quartz differed for the lower section of the core（10.6-14.7 m）,and the deviation gradually increased with depth.The medium-grain（MG;38-63μm）fraction produced overestimated ages because of the averaging effect,while some coarse-grain 2（CG2;90-150μm）fraction samples produced underestimated ages because of insufficient bleaching.Regarding samples with unsaturated quartz,the K-feldspar ages from the IR₅₀ signal are more accurate than those from the p IRIR_170/225 signals.Based on quartz,the p IRIR method produces overestimated ages relative to the OSL method,and the difference between the ages increases as the associated temperature increases.3)Samples from the FN1 core produced ages ranging from 25.4 to 0.8 ka based on the OSL method.According to a chronological framework starting from the Late Pleistocene and a palaeoenvironmental index,the sedimentation rate is partitioned into three main periods.Sedimentation rates during the periods between 25-21 ka and<7 ka are higher than those for the period between 21-7 ka.These results suggest that the sedimentation rate was probably controlled by sea-level changes.