Application Of XRF Core Scanning Technology In Holocene Sea Level Change Reconstruction In Ningshao Plain

With global warming,sea level rise has become one of the most important environmental issues all over the world.Because of sea level change's sensitive response to climate change,it is one of the most important parameters and research fields regarding the study of global climate change.Sea level change can be global and regional at the same time due to its multiple causes.Sea level change shows a global pattern due to worldwide factors such as ice sheet melting and global temperature change.It also differs from area to area due to regional causes like regional subsidence and tectonic movements.Sea level change during Holocene was mainly controlled by global ice volume and sea temperature.Therefore,regional sea level change shall fit the global sea level change.Since Mid 20th Century,researchers have been doing long-term and systematic study over sea level change in the Eastern China.A great amount of fundamental researches were done by scientists such as Yang Huairen,Xie Zhiren and Zhao Xitao.With the development of global change,the study of sea level change is becoming more and more important in the 21st Century.The Yangtze Delta in east China is the area with the most researches regarding sea level change.However,due to its position between Yangtze River and East China Sea,this area suffers from strong land-sea interactions and frequent river course changes.As a consequence,it's difficult to get a continuous and high-resolution sedimentary sequence from the Yangtze Delta.What's worse,the subsidence is too complicated to calibrate.Therefore,the sea level change recovered from the Yangtze Delta can hardly be compared with a global one.To avoid these problems,our research area is on Ningbo-Shaoxing plain(Ningshao plain),which is south to the Yangtze Delta with Hangzhou Bay in between.To be more specific,our research area is a small basin in east of Ningshao plain,called Yuyao basin.It is a small basin with a nearly EW direction between mountains.With Cinan mountains in the north and Zhoushan islands in the east,Yuyao basin is a relatively closed and stable reservoir compared to Hangzhou Bay and continental shelf of East China Sea.Sediment in Yuyao basin can be well protected from tides and waves.Therefore,the sedimentary sequence is more complete and continuous,which makes it a suitable place to study sea level change in high resolution.To control the stratigraphy of Yuyao basin,three cores were drilled.One is in south of Yuyao basin numbered HMD 13 while the other two were taken in north of Yuyao basin numbered TLS13 and TLS1402.Stratigraphic differences will be directly showed in element abundance and elemental geochemistry is about different elements indicate different environmental and climatic change.Here we use AVAATECH XRF(X Ray Fluorescence)core scanner to obtain relative element abundance change of a core in high resolution and aim to discover a proxy to tell marine sediment from continental sediment.XRF core scanner is widely used on marine cores to get element intensity(relative elements abundance)change on the profile with little preparation and nondestructive,efficient and high-resolution scan.Elemental intensity or ratio curves are widely used in core comparison or indicating paleoenvironment or paleoclimate changes.Three cores were scanned by XRF core scanner and element results were compared with sedimentary sequence.Calcium intensity shows an obvious consistent change with marine-continental sediment change while calcium intensity rises during marine sediment.Traditional XRF analysis was also taken in TLS13 core to show whether the results from XRF core scanner are reliable.The correlation between calcium intensity from XRF core scanner and calcium concentration from traditional XRF analysis is up to 81%.Therefore we regard the calcium intensity from profile scanning is reliable to show concentration change in the sediment.Besides that,diatom,foraminifera and ostracoda were analyzed.These are direct indicators for marine environment and by comparing calcium intensity with marine diatom concentration,foraminifera and ostracoda,it is more certain that calcium intensity can be used as a marine environment indicator.Combining calcium intensity curves with age data from 14C dating,a rough sea level change history was recovered from the sediment in Yuyao basin.Before 9 ka B.P.,Yuyao basin was still continent and covered with hard clay.Around 9 ka B.P.,sea level rose and reached this area while about 8.5 ka B.P.this basin was under sea level.During 8.5-7 ka B.P.,sea level rose rapidly and was close to present sea level.Around 7 ka B.P.,sea level rise began to slow down while terrigenous sediment was continuously brought by river system.As a result,the continent started to develop and pushed coastal line back.During 7-6.5 ka B.P.,sea level rise and continental growth made coastal line shifted back and forth.Since 6.5 ka B.P.this area is dominant with continental development with sea regression and land expanding.