The TLS1402 Pore Diatom Recorded The Evolution Of The Holocene Paleoenvironment In The Ningshao Plain

Since the 20th century,the rise of the global sea-level rise has great impact on the environment of costal region,which becomes one of the largest environmental problems around the world.It is particularly important to research on the rule of global sea-level variation as well as to exploration the relationship between human beings and climatic environment.Ningshao Plain,located at the south coast of Hangzhou Bay,adjacent with East Sea,is a northwest-southeast basin.During the last glacial period,this area cultivated the first hard clay layer and then developed a variety of Neolithic Cultures.The rice remains unearthed in these cultural sites result that the site areas become important to research on rice agriculture source.During Holocene period,the influence of monsoon climate on this area gave rise to sea-level fluctuation and frequent sea-land replacement.Due to the shielding effects of Cinan Mountains and Zhoushan Islands,it was free of the direct scour of seawater during transgression and hence their sediments are complete and continuous.The unique geographic and historic conditions provide ideal place for studying the relationship between sea-level fluctuation,flood,storm tide and human settlement development.The study found that the grain size and the combination of diatom of the sediments of core from Tianluo Mountain has strong relationship to Ca/Ti,foraminifer,and ostracod.It reflects the ancient environment and sea-level fluctuation of this area:1.Before 8.4ka B.P.the grain size of the sediments in this place is relatively large.Freshwater species diatom occupy the main position.There are a few foraminifers and marine ostracods.The feature environment should be shallow water,occasionally affected by sea water.2.During 8.4?7.8 ka B.P.the majority of sediment is silt.The amount of saltwater diatoms,Ca/Ti,as well as the abundance and amount of types of foraminifer and marine ostracod decrease with the increase of depth.According to a variety of data,sedimentary rate in this period is relatively large,which means that sea level rose fast in this period.The research area is probably point bar of bay or inner sublittoral zone.3.During 7.8?6.3 ka B.P.,the majority of sediment is silt.Both the curves of saltwater diatoms and that of Ca/Ti have three variations.The abundance of foraminifer and marine ostracod decreases.Total solar irradiance and sedimentary rate generally decrease at the beginning and then increase.Compared to 8.4?7.8 ka B.P.,sedimentary rate in this period is smaller.In this stage,sea level still tends to rise.The research area is affected by the interaction between saltwater and fresh water.It could be an alternate environment between intertidal zone and shallow water marsh.4.Since 6.3?5.0 ka B.P.,the majority of sediment is silt and freshwater species diatom is the majority.Both the amount of saltwater diatoms and that of Ca/Ti are manifested as low value,but appeared a small peak once,which might resulted from the seawater intrusion.There is no foraminifer and marine ostracod but there is chara.The research area in this period mostly accepted fresh water of the river and should be terrestrial shallow water marsh.Generally,our research has great significance on the study of sea-level change in Ningshao Plain and its relationship between prehistoric civilization.