DISTINGUISHING SEDIMENTS FROM THE YANGTZE RIVER AND YELLOW RIVER USING MAGNETIC MINERAL INCLUSION WITHIN SILICATES
Environmental magnetic parameters have been widely used in China to differentiate sediment sources in coastal and marine deposits,specifically those from the Yangtze River and the Yellow River.It is important to consider the influence of early diagenesis on magnetic minerals,as they are sensitive to redox conditions.Magnetic mineral inclusions within silicates are not affected by diagenesis and can provide reliable source discrimination.In this study,we collected 19 samples from the Yangtze River(11 samples from the floodplain at Datong,Anhui Province)and the Yellow River(5 samples from the floodplain of the modern Yellow River Delta;3 samples from the tidal flat of the Old Yellow River Delta).We extracted magnetic mineral inclusions from bulk and particle-sized sediment samples(i.e.,＜16 μm,16～32 μm,32～63 μm,＞63 μm)using published methods.The samples were treated with excess 10 mol/L HCl,heated in a water bath at 80 ℃ for 5 hours,and then allowed to react at room temperature for 19 hours.After treatment,the samples were centrifuged,acid-washed,and dried.The magnetic characteristics of the treated samples were attributed to magnetic mineral inclusions within silicates.The aim of this study was to develop a new approach for distinguishing sediments from the Yangtze and Yellow Rivers.The results showed that concentration-related magnetic parameters(x,SIRM,xARM,HIRM)were reduced to less than 10％of the untreated bulk sediments after HCl treatment.The HCl-treated samples were nearly saturated in a 300 mT magnetic field,indicating a dominance of low coercivity ferrimagnetic minerals in the silicates.The parameters related to the size of magnetic mineral particles(xARM/SIRM and xARM/x)increased significantly,indicating finer particles in the inclusions compared to the untreated samples.The treated Yangtze River sediments had higher SIRM,xARM,and HIRM values compared to the Yellow River sediments,indicating higher contents of ferrimagnetic and imperfect antiferromagnetic minerals in the inclusions.The variations of magnetic parameters with grain size showed that SIRM and HIRM of the inclusions in both river sediments increased with increasing grain size,indicating an increase in ferrimagnetic and imperfect antiferromagnetic mineral contents with larger grain sizes.Due to the numerous tributaries and complex rock types in the Yangtze River catchment,magnetic parameters of the inclusions showed a larger range compared to those of the Yellow River.The Yellow River sediments were mainly derived from the Chinese Loess Plateau,which was well-sorted and mixed during aeolian transport from Asian deserts and had a lower content of magnetic inclusions but relatively uniform magnetic parameters.This study demonstrates that scatter plots of SIRM(saturation isothermal remanent magnetization)and S-100,as well as principal component analysis of magnetic parameters of silicate inclusions and thermomagnetic analysis,can effectively distinguish sediments from the Yangtze and Yellow Rivers.On the SIRM-S-100 scatter plot,the S-100 values of the Yangtze River samples decrease significantly with increasing SIRM,indicating a correlation between higher coercivity and higher magnetic mineral content.The principal component analysis of magnetic parameters shows that the first principal component has higher loadings on SIRM,xARM(anhysteretic remanent magnetization susceptibility),and HIRM(hard isothermal remanent magnetization),while the second principal component has higher loadings on S-100 and S-300.The first and second components reflect the content and type of magnetic minerals,respectively.The Yangtze River samples have higher positive scores on both the first and second components compared to the Yellow River samples.The temperature-dependent magnetic susceptibility analysis reveals a clear Hopkinson effect in the＜16 μm fraction of the Yangtze River samples.These findings present a new,cost-effective,and efficient approach for source analysis of sediments in China's coastal areas.
inclusionenvironmental magnetismprovenanceparticle size separationthe Yangtze Riverthe Yellow River
万方数据
维普
