Research On Characteristics Of Holocene Sediment And Paleoclimate Change In Pingtan Island Adjacent Seas

There are so many natural resources and very vast space in the ocean world, andthe islands, as our national defense frontier, have very high value of security, economyand environment, they are also playing important role of marine ecological system.With the Western Taiwan Straits Economic Zone become the national strategy fromthe regional, Pingtan Island will have the chance to develop fast than ever before.Based on grain size, detrital mineral, clay mineral, SEM and organic matter δ¹³C_TOCanalysis of core sediment in Pingtan Island, the vertical variation characteristics ofenvironmental parameters such as grain size parameter, δ¹³C_TOC, TOC content, C/Nratio, carbonate content were elucidated. In contrast with previous research results,sedimental characteristics and paleoclimatic change of Holocene were discussed instudy areas, the sediment source and its transportation medium were also studied. Themain study results are as follows:（1） TS sediment core can be divided into8different sections: A, B, C, D, E, F, Gand H, each of them indicated different period and procedure of sea lever change.Grain size frequency curve could be classified into3types: type α, type β and type γ,most of section A, B, C and F sediment are type β, section E, G and H are type α,meanwhile type α and type β are the dominated in section D. Among the detritalminerals, the average content of light mineral is98.14%, while the heavy mineral isonly1.86%. Magnetite, hornblende, tremolite, zircon, biotite, pyrite, white titaniumare the main kinds of a total22kinds of heavy minerals, a slight change in the verticalcan be observed of heavy mineral assemblage. Compared with the sediment grain sizeparameters, the changes of δ¹³C_TOC, TOC content, C/N ratio and carbonate contenthave a little lag. Marine authigenic organic matter play an important role of totalorganic matter in the sediment, and carbonate is most terrigenous.（2） DX sediment core can be divided into2different sequences: Ⅰand Ⅱ,section Ⅱsediment relatively formed in shallow water and high energy environment. Grain size frequency curve could also be classified into3types: type a, type b andtype, all of section Ⅰsediment are type a, while sectionⅡ had all of3types andchanged alternately.23kinds of detrital minerals can be identified from DX coresediment, the average content of6kinds of light minerals can reach91.25%, but thatof the other19kinds of heavy minerals just reach8.75%. Epidote, apatite, ilmenite,hornblende, augite and pyrite make up the main heavy mineral assemblage, whichhave little change in the vertical. Clay minerals are comprised of illite, chlorite,kaolinite and smectite, as the main clay mineral, the average content of illite andchlorite can reach49.68%and30.68%, while the average content of kaolinite andsmectite is smaller relatively, only reach11.66%and7.99%.（3） Under SEM, the composition of DX core sediment was consistent with theresult of detrital mineral analysis. The surface and crystalline form characteristics ofquartz and authigenic pyrite indicated that section Ⅱ sediment formed in strongerreducibility and high energy environment. The result of Semi-quantitative elementalanalysis showed that the character of lamination was consistent with grain sizeparameters, and chemical element Si, Al, Fe and K comprised the main components ofDX core sediment, however the sediment also contained a little content of Na、Mg、S、Cl、Ca、Ti element and so on. Obviously, Fe element, the content of pyrite underdetrital mineral and SEM analysis had the same vertical variarion.（4） The dynamic condition of modern sedimentary environment is controlled bytide in Pingtan Island adjacent sea, it also was influenced by wind, precipitation andrunoffs. The coarse particles component of sediment was mainly from bedrockweathering and erosion in Pingtan-Nanri Islands, meanwhile, some fine particles hadthe same source. Except that, the suspended matters which come from the Minjiang,Yangtze River, Zhemin Coastal Current and other rivers along the coastline made upthe supplement of fine particles.（5） In the early stage of early Holocene （include stage A, B）, the sea level rose, theclimate became warm from dry and cool in Pingtan Island adjacent sea. However, thesea level keep stable and the climate remain warm in the middle stage, while the latestage of early Holocene was a period of sea level falling, climate warming and reached the warmest period. There were twice large scale marine transgression inmiddle Holocene（stage C、D、E、F） in study area and the sea level was higher thantoday. In the early and middle period of middle Holocene, the climate was warm andmoist, and became a little cold in the late period of middle Holocene, then the climatechanged to warmer again. On the whole, late Holocene （stage G、H、Ⅰ、Ⅱ） was aperiod of climate cooler and reducibility stronger. There was a regression in the earlystage of late Holocene, and the sea level was stable after the regression. However, thetwo stages had the same climate change from dry and cool to warm.