Study On Geochemistry Characteristics And Sources In The Mud Area Southwest Of Cheju Island

The East China Sea continental shelf receives large quantities of sediments from the Changjiang(Yangtz) and Huanghe (Yellow) Rivers,which records the change of rivers' characteristics and climate. In order to study sedimentation processes,development and evolution of the East China Sea (ECS) shelf and rivers' effects on the marine sediments in detail, it is necessary to identify the Changjiang and Huanghe Rivers' sediments. In this paper, The<2um sediments samples from the mud area sounthwest of the Cheju Island and sediments of <63um from the Changjiang and Huanghe Rivers are choosed. Trace elements, REE (Rare Earth Element) and grain size characterics of these sediments are anlaysed.The results show that contents of trace elements and REE in the Changjiang River are different from those of Huanghe River. Contents of elements such as Co, Cr, Sc, Ti, La, Nd of <2um are higher than those of the Huanghe River. Contents of trace elements and REE decrease with increasing grain size in the sediment of the Changjiang River. However, contents of haven' t diciplines with the changes of grain size in the Huanghe River. Distributional characteristic of the rare earth elements in sediments of the Changjiang is similar to those of Huanghe Rivers. LREE (Light Rare Earth Element) and HREE (Heavy Rare Earth Element) in sediments of the Changjiang River are charactered by more obvious fractionation compared to those of the Huanghe River. And the difference of REE contents among various grain size in the Changjiang River are smaller than those of the Huanghe River. The content of HREE in the fraction less than 2um of the Changjiang River are lower compared toHuanghe River. The factors influencing geochemistry characteristics in the Changjiang River are geographical features, sources and different complexation of REE under different PH.Based on the data of grain size, AMSHC dating and the content of elements, sedimentary records and their response to climate changes in the B2 and B3 cores located southwest of the Cheju are analyzed. From the top to 90cm in B3 core and the B2 core consist mainly of clayed silt, which indicate the sedimentary environment is steady since 2. 3kaBP. The trace elements and REE contents in the clay fractions are close to those in the Changjiang and Huanghe Rivers. According to comparing the correlative parameters of elements in the three area such as DF (discriminant function) , the parameter values of southwest mud area of Cheju Island are similar to the clay fraction in the Huanghe and Changjiang Rivers, but they are more close to those of the Huanghe sediments. The sediments in the mud area are impacted by sediments from the Changjiang River and biological activities partly.The element distributions in clay fraction from 90~230cm of B3core are also similar to those from Changjiang and Huanghe Rivers, so sediments before 2. 3kaBP in the mud area are mainly from the Changjiang and Huanghe Rivers.In the Holocene, the evolution of the mud area is controlled by sediments from the Huanghe River, the Yellow Sea Warm Current and the Yellow Sea Offshore Current and climate factors , etc. The geochemistry characteristics and grain size composition of the sediment in whole core is corresponding with the changes of the climate, so the whole core can be divided into 6 stages. l)219~~780aBP, colder, the contents of trace elements and REE are all higher. 2)780~1450aBP, relatively warm, the contents of trace elements and REE are all relatively lower except Sr. 3) 1450~1900aBP, relatively cool , the content are higher than the abovestage 4) 1900~2300aBP, relatively warm, the contents of are relative lower. 5) 2300~10553aBP, the climate changes can be subdivided 4 periods, the content of trace elements and rare earth elements recorded this four sub —stages. 6) 10553~12231aBP, the climate turn to cold abruptly and the content of trace elements and rare earth elements increase at UKaBP, which respond to the Younger Dryers.