Geochemical Characters Of The Sediments And Its Significance On Environmental Change During Mid-Pleistocene In Changchun Area

Northeast China Plain is the largest alluvia l pla in. The population isconcentrated and its productivity is quite developed. Furthermore it is an importantagricultural, anima l husbandry base and oil producing area. Especia lly in thecountry's energetic revitaliza tion of the old industria l bases in northeast Chinatoday, Quaternary changes research in the natural environment in the NortheastPlain is not only of theoretica l significa nce, but also of a major practica lsignifica nce for the nationa l economy development. Changchun City in thenortheast region has a pivota l position. Therefore, this paper's research object issediments in the Mid-Pleistocene from Changchun HDBZK-1 hole. We attempt tostudy the distribution of sedimentary sequence, the sediment materia l source of thestudy area, to discuss the sedimentary environment and sedimentary sequencerespond to globa l clima te changes.During the process of research, we ma inly use the field observation records,GPS pointing device, digital camera, thermal luminescence dating, particle sizeanalysis, pollen analysis and geochemica l analysis, by dint of Winner2000 laserparticle size analyzer, ICP-MS7500a inductively coupled plasma analyzer,SPSS16.0 software.Through particle size analysis, the characteristics of sedimentary particle sizedistribution, the sediment materia l source and cause of formation, the ancientsedimentary environment and paleoclima te change are studied. Particle sizeanalysis shows that sediments of this area belong to the silt particle type, with asize composition of the sma ll - ma inly fine silt. The sediments'grading is moderate , ma inly to the nega tive side, the number of midd le-state. Sediment thick nesschanges in the avera ge particle size characteristics of the study area can becharacterized evolution of the environment, combined with the age analysis, whichreflects that from 69.581 to 60.448×104aB.P., relatively dry clima te changedrapid ly into relatively humid, from 60.448 to 20.252×104aB.P., gradua lly changedfrom relatively humid to relatively droughty, from 20.252 to 12.636×104aB.P., theclima te has undergone four-time"humid→droughty→humid"changes. Accordingto the results of distinguishing cause of formation and discrete plot, it is showedthat the deposit environment of research area is compound of windborne andalluvia l deposition.Through pollen analysis, we can rebuild the ancient vegetation succession ofthe study area in the Mid-Pleistocene, discuss the evolution of ancient clima te stage,and then compare with Europe, China Lusha n Mountain and the northeasternregion ice age. It is found that they have good correspond ing relationship. Theevolution of ancient vegetation in this area can be divided into three stages in themass. In the early Mid-Pleistocene (I-IV pollen zone), correspond ing to the eveningof northeast China's third interglacia l, desert grassla nd ecological backgrounddominated the ancient vegetation. In the Mid-Pleistocene (V-VII pollen zone),correspond ing to the Northeast China's fourth glacia l (Nuomin River glacia l age),desert vegetation to ecological background was in the ascenda nt. In the late Mid-Pleistocene (VIII-IX pollen zone), correspond ing to the forepart of northeastChina's fourth interglacia l, ancient vegetation were also desert ecologicalbackground.In order to discuss the sediment materia l source and sedimentary environmentchanges, to distill paleoclima te environment change information of the Changchunarea, we studied the elements of column-like sediments. 24 major elements of regular and trace content are analyzed using R-cluster analysis and R-factoranalysis. When the dista nce factor is fixed at five, seven element combinations canbe obtained. Then we analyze source instructions significa nce of each elementcombination. In the cumula tive varia nce contribution of 90.9 percent, we can getfive major factors F1, F2, F3, F4, F5, which impact chemica l composition ofsediments, of the first three factors, which contribute to higher varia nce. Theregular, trace content elements of HDBZK-1 hole have a good symbioticrelationship and their ma in materia l sources include la nd-based sources of debris,the source of volca nic origin and biologica l substa nces, but also to some extent bythe impact of self-role.By introducing six kinds of clima te parameters, paleoclima te evolution in thestudy area can be divided into three gyres: in the early Mid-Pleistocene (from boredbottom to about 27.200×104aB.P.), experiencing a"cold droughty→moderate cool,relatively humid→cold droughty"process of change, for the first clima te gyre, inthe Mid-Pleistocene (from about 27.200 to 12.271×104aB.P.), more frequentfluctuations in the clima te and environment, on the whole, cold and droughty, forthe second clima te gyre, In the late Mid-Pleistocene (from about 12.271×104aB.P.to bored top sector), the clima te had experienced"cold droughty→moderate cool,relatively humid→cold droughty"process of change, which has proven that in thelate Mid-Pleistocene the clima te appeared warming signs, for the third clima te gyre.This conclusion accords with the results of pollen analysis.