The Provenance Of Quaternary Red Earth On The Terrace Of The Min River In Northern Fujian And Its Environmental Implication

Red earth in southern China generally distributed in the south of 30°N tropical and subtropical monsoon climate region,covering more thal two million km2.These widespread red earth are believed to be the products of the environmental and climatic changes under the glacial and interglacial cycles in medium and low latitudes,which has been aroused the attention of scholars home and abroad.Study of source material can involve sediment source of parent material and the characteristics of the change,interpreting environmental evolution from weathering,erosion,transportation to the deposition of the sediments.In this study,the Daheng Quaternary red earth section in the mid-south subtropical areas in Fujian has been taken as the main research object,the nearby Longchuanshan red earth profile and the representative samples of the piedmont alluvium,bedrock,weathering crust,river surface sediments and laterite from the potential material sources have been taken as contrastive study objects.The provenances of the Min river Quaternary Red Earth in the northern Fujian have been explores through the System analysis of geochemical elements and partical size of these samples.Based on the systematic analysis of geochemical elements,partical size,OSL,magnetism,and chromaticity of Daheng section,the regional environmental evolution since late Pleisgocene in northern Fujian has been preliminary research too.The study will provide important references for understanding the role of Fujian red earth in East Asian monsoon and environmental evolution.Results are following:(1)The geochemical elements features of Quaternary Red Earth section in northern Fujian:Daheng section ?REE(total content of rare earth element)and LREE/HREE(the value of light rare earth element than heavy rare earth element)mean value is 227.22 ?g.g-land 13.02.The values of ?REE and LREE/HREE vary largly through the section.Distribution patterns of Red Earth element in Daheng section are similar to the Min river upstream surface sediments and the Sanmen village,Fang village,Daren,Lukou,Shanglong and Longchuangshanlu Red Earth near of Min river.87Sr/866Sr distribution range of representative Earth samples in Daheng section are 0.735499?.759661,143Nd/144Nd distribution range are 0.511893?0.511944.?Nd(0)distribution range are-13.63?-14.54.Sr-Nd isotope values of Red Earth element in Daheng section are similar to Longchuangshan and Jianou Red Earth near of Min river.These show that Red Earth element geochemical characteristic in Daheng section of Min river are similar to those of the neary piedmont alluvium,weathering crust,soil profile representative samples and river surface sediments,which have shown the regional transportation and deposition of the Daheng section.Most easily leached elements of Daheng section red earth basicly leaching after migration,reflecting hot wet sedimentary environment overwall.(2)The source of Quaternary Red Earth in northern Fujian Min river analysis:through the analysis of geochemical elements,we conclude sources and physicochemical characteristic of fine particles in Red Earth sediments of Min river Daheng and Longchuangshan scetion geochemical elements have obvious difference with the northern China loess-paleosol,Xiashu loess and aggradation red earth,but similar to weathering crust and the bedrock.Meanwhile,similar physicochemical characteristic and material source of Daheng and Longchuangshan red earth scetion show that,sedimentary characteristics of fine particles red earth sediments in Min river are more likely uniform,all are alluvial-pluvial and slope deposition.Coarser particles in Red Earth sediments that collect in Min river coast are not uniform.Their material source should be mainly sediments that forms in the influence of rainfall,water and geological processes,and complete handling alluvial in-place short diatances.Overall indicating northern Fujian Min river Quaternary Red earth sediments are close to the source material deposition.(3)Environmental significance of northern Fujian Min river Quaternary Red earth indicating:The systematic analysis of geochemical elements,partical size,OSL,magnetism,and chromaticity of Daheng section have shown that the gravel layer at the bottom of Red earth in Daheng section may be an ancient riverbed of Min river tributary,8.9-11.3 m are flood land facies,and sediments are from river transportation and surrounding material accumulation.6.5-8.9 m are the ancient flood sediment,which are the results of rapid depositions that come from larger ancient flood carrying much detrital material such as soil or weathering crust on the terrace.4.5-6.5 m is the sedimentary dynamics change phase of Red Earth.0-4.5 m are slope sediments,which come from proximal high ancient detrital material such as soil or weathering crust that forms under the erosion of rainfall or profile runoff.In northern Fujian,the Quaternary Red earth section is river alluvial-pluvial and slope deposition.Fujian's climate was warm and moist in the MIS3 phase,sea level expansion enhances the monsoon circulation on the southeastern coast of China,leading to increased rainfall in northern Fujian.Then,Quaternary Red Earth terrace develops in the Min river.Red Earth sediments is mainly proximal substances alluvial-pluvial and slope deposition,the possibility of aeolian deposition is very small.This may indicate that,although the dust in the north could reach Fujian under the winter moonson,the transmission path is longer,the material quantity is less,the rainfall is rich,and Fujian terrain elevation difference is bigger,it's difficult to completely preserve and record for sediments.