Luminescence Dating On Core ZK0092 & ZK0099 From Foshan,Pearl River Delta

The Pearl River Delta（PRD）lies in a warm-and-wet zone that is sensitive to land–sea interaction in the southern China and influenced by the East Asian summer monsoon（EASM）,as well as the only route that the Pearl River debouches into the South China Sea.The Quaternary strata of the PRD preserve a wealth of paleoclimatic information and are divided mainly based on stratigraphic chronology.However,different dating methods have led to debate on two problems concerning the Quaternary geomorphic evolution of the PRD among researchers:1)how many sedimentological cycles did the PRD develop since the Quaternary,and 2)what are the age ranges of these sedimentological cycles.To better answer the questions mentioned above,this study applied the luminescence and ¹⁴C dating techniques to constrain the chronology of Quaternary sediments of cores ZK0092 and ZK0099 drilled from Foshan City in the PRD.Combining field investigation,previous studies,and ages based on luminescence and ¹⁴C dating,this study aims to assess the geochronology of core ZK0092 and ZK0099 in the PRD,and the chronology of lower marine layer and its relationship with sea-level change.The results are as follows:（1）Three different materials from a depth of 14 m of core ZK0099 yielded AMS ¹⁴C ages of118±76 cal a BP（plant）,176±86 cal a BP（charcoal）,and 2226±56 cal a BP（organic sediment）.There is a large difference among ages of different materials from the same depth,probably resulting from carbon contamination out of multiple erosion–transport–deposition cycles under an environment with strong stream power and complex depositional processes.（2）The AMS ¹⁴C age of sample from a depth of 20 m of core ZK0099 was>43500 a BP,which exceeds the upper limit of ¹⁴C dating and thus should be regarded as the minimum age.The feldspar luminescence age of adjacent sample（19.9 m depth）was 89±6 ka,much older than the¹⁴C age.（3）The feldspar luminescence dating of sediment from different depths of cores ZK0092 and ZK0099 showed that,in core ZK0092,sediments at depths of 3.5 m,5.9 m,and 10.7 m yielded corrected ages of 58±9 ka,69±5 ka,and 92±7 ka,respectively,and in core ZK0099,sediments at depths of 16.8 m,19.9 m,23.4 m,and 32.9 m yielded corrected ages of 85±6 ka,89±6 ka,and 238±16 ka,and 210±17 ka,respectively.Dating results of cores ZK0092 and ZK0099 agreed with the stratigraphic order and thus supported the reliability of feldspar luminescence dating.（4）According to the dating results and sedimentological features of core sediments,core ZK0092 was divided into 4 sedimentological units（U1～U4）with luminescence ages between 58and 92 ka.The age range of U3 was 69～92 ka,around the marine isotope stage（MIS）5,suggesting the lower marine layer.The age range of U2 was 58～69 ka around MIS 4,suggesting that was formed in a terrestrial environment when sea level was low.（5）According to the dating results and sedimentological features of core sediments,core ZK0099 was also divided into 4 sedimentological units（U1～U4）with ages between 0.31 and238 ka.The age range of U4 was 210–238 ka around the MIS 7,and whether this unit belonged to terrestrial or marine layers could not be decided with available data.The age range of U3 was 85～89 ka around MIS 5,and this unit should be the lower marine layer.Quartz OSL age at depth of14.8 m is 48±4 ka,representing that layer at the top of U3 was driven by fluvial process during MIS 3;¹⁴C age of plant（ZK0099-14C-01 plant）and charcoal（ZK0099-14C-01-charcoal）in U2 at depth of 14 m is 0.12±0.08 cal ka BP and 0.18±0.09 cal ka BP,respectively,quartz OSL age in U1 at depth of 14.8 m is 0.31±0.03 ka,suggesting that U2 and U1 was formed since the Holocene.The luminescence dating results showed that around the Foshan area in the PRD there were strata as old as the MIS 7 underlying lower marine layer,which itself was formed in MIS 5,and the upper terrestrial layer was formed in MIS 4～3.