Analyses Of Sediment Grain-Size Spectra And The Study As Proxy Of Marine Environment Change

There are two new methods established to analyze sediment grain-size spectra. Grain-size spectra of 6 surface sediment samples and 5 sediment cores which were cllected from 4 areas that near shore of Qindao,Jiaozhou Bay,near shore of Xinghua Bay,Xiamen Bay,are analyzed by these methods. Grain-size components are numerical partitioned and its the environmental implications were studied.Take Jiaozhou Bay surface sediment for instance, spectra-stripping and Origin analysis method are compared. It's better to identify overlapped peaks using Origin analysis method. For times of iterated calculation, we can get better fitting results. However, spectra- stripping method is the base of Origin analysis method and has its own advantage. In the course of practical analysis, we give priority to Origin method and use spectra-stripping method as supplements. There are 4～5 components in Jiaozhou Bay surface sediments, the 5th component appeared only in A3,B3 and C3 stations. Grain-size components in polymodal sediments reflect different transportation or depositional process. The results indicate that one component usually contains two or more traditional grain-size classes.Grain-size parameters of the core C23 from Jiaozhou Bay are calculated and the grain-size spectra are analyzed. Mean grain size of the core is 10.9～47.0μm, poorly sorted, coarse skew, narrow kurtosis. There are 7 components in core C23, which grain size ranges are 4～6μ?m,12～17μ?m,25～44μ?m,36～94μ?m,56～257μ?m,133～418μm,262～518μm and contents are 17～53%,8～47%,0～37%,0～51%,1～29%,0～29%,0～50%å’Œ0～5%. Establishing time series using sedimentary rate from documents, and comparing profiles of grain-size components and meteorological data, we can deduce the environmental implications of the components.Grain-size parameters of the core A2 from near shore of Qindao are calculated. Mean of grain size is 12.3～293.6μm, poorly sorted, fine skew, narrow kurtosis. There are 9 grain-size components in sediments, which grain size ranges are 4～5μm,13～16μm,32～41μm,52～86μm,90～263μm,241～345μm,282～489μm,429～736μm,811～877μm and contents are 8～44%,14～50%,10～27%,0.6～21%,0.6～7%,0.2～17%,0.1～13%,0.1～33%,0.8～23%. From the profiles of grain-size component and time series,it is considered that the layer which coarse components appeared corresponded to the year storm surge happened⁴⁰K,²¹⁰Pb,¹³⁷Cs,²²⁶Ra,²²⁸Ra,²²⁸Th,²³⁸U in two cores from near shore of Xinghua Bay are detected byγspectrometer. Time series are established. Sedimentary rates of core ZK6 are 0.607cm/a and 0.737cm/a in the layers of 0～43cm and 50～100cm respectively. ZK18's sedimentary rate is 0.180cm/a. Sediments of two cores are filtrated into 4 fractions: >0.25mm,0.25～0.125mm,0.125～0.063mm and <0.063mm. The profiles of each fraction are discussed. Grain-size spectra of the typical sediment core ZK18 are analyzed. There are 10 components in this core, which grain size ranges are 4～11μm,12～22μm,28～44μm,50～111μm,74～200μm,162～244μm,213～344μm,266～446μm,450～633μm,699～1710μm and contents are :5～40%,1～55%,0～28%,0～10%,0～30%,0～35%,0～32%,0～23%,0～23%,2～75%. In Xinghua Bay, earthquake and storm surge frequently happened, so changes of sedimentary rates and profiles of grain-size components are reasonable. Profiles of 7 radionulides in core XD2 and core ZLO are determined. The sedimentary rated of core XD2 and ZLO are 2.62cm/a and 2.43cm/a. There are 4 grain-size components in two cores. For core XD2, peak locations of each component are 4～6μm,11～15μm,22～40μm and 52～89μm and contents are 36～49%,42～54%,6～17%,0～4%. For core ZLO, peak locations of each component are 4～6μm,12～15μm,33～40μm,63～104μm and contents are 37～48%,38～52%,6～18%,0～7%. The Xiamen Gulf is an open sea area with regular semidiurnal tides, the tidal currents and residual currents are the main powers which mold its modern landform. Profiles of grain-size components of core ZK6 and ZK18 indicate the changes of tidal and residual current systems. Compared with grain-size spectra of 6 sediment cores from 3 different sea area, we consider that there are two fractions in most grain-size spectra: fine fraction and coarse fraction. The fine fraction is composed by the 1～5 components, while the coarse fraction is composed by several components. Generally, the former five components are ordinary components, called 5μm component, 15μm component, 36μm component, 70μm component and 150μm component respectively. The first component is mainly transported by upper level air flow, its percentage changes represented the aridity of source area. The 2^th～5^th components, are transported by water under normal weather condition, its percentage changes reflected the different current system varieties. The 6^th～10^th components are carried by storm surges. The appearance of them indicated that there are typhoons or storm surges in corresponding years.