Distribution And Physical And Chemical Characteristics Of Fe-Mn Nodules In A Deep Soil Developed From Loess In Shenyang

Fe-Mn nodules as a new body of oxidation-reduction environment alternately formed reflects the formation of soil environment and soil properties,which is usually used for diagnosis and classification,Fe-Mn nodules has an important role in the interpretation and reconstruction of paleoclimate and paleoenvironment and ancient landform.As an important carrier of soil adsorption,Fe-Mn nodules are involved in the chemical reactions in soil.With the deterioration of the environment,Fe-Mn nodules become more and more important in remediation of contaminated soils,which has become a hot research topic.Soil survey in the past,in the northeast region developed in loess,in the highland landscape(usually underground water level in deep soil),discovered the existence of Fe-Mn nodules widely.Hower,their formation mechanism is not clear.Therefore,this study choose the deep section of Shenyang area developed in Loess Soils(0?450 cm)as the research object,according to the soil layer in the field by field observation and sampling,extraction and separation of Fe-Mn nodules in various layers of wet sieving method in laboratory,using geochemical method,X-ray fluorescence spectrometry method and stereo microscopy,quantity,Fe-Mn nodules distribution in the soil profile in the size and colour of morphological characteristics and geochemical elements.The purpose is to lay a theoretical foundation for a deep understanding of the distribution characteristics and formation mechanism of soil iron manganese nodules and to provide a scientific basis for further study of soil genesis and classification and interpretation of regional paleogeographic environment.Some meaningful results were listed as follows:(1)Fe-Mn nodules were mostly foud in regular shape,spherical or ellipsoidal,with color such as bright-brown,brown,dark-brown,and black in the Shenyang loess.They have different abundance in different size range.The abundance of 0.5?2 mm,>2 mm,and 0.1?0.5 mm Fe-Mn nodules is highest,medium,and lowest,respectively.The average content of>0.1 mm Fe-Mn nodules is 10.59 g·kg-1.Most of>0.5 mm Fe-Mn nodules have band structure,and the larger Fe-Mn nodules,the more rings.The dark brown bands interbedded with the black band,and the dark brown band interbedded with the brown band were observed.The brown core and the black core were observed.A large band of Fe-Mn nodules has thin rings which indicate that the formation of Fe-Mn nodules has experienced several strong redex and was long enough to record the soil formation environment.(2)The Fe-Mn nodules in different size have different elemental enrichment.The elemental enrichment of Fe-Mn nodules in 0.5-1 mm was slightly greater than that in 1-2 mm Fe-Mn nodules.Forty out of 53 elements accumulated in the Fe-Mn nodules.The elemental enrichment order from high to low is Mn,Co,Mo,Pb,Ce,Cd,P,Sb,Ni,V,Fe,Ba,Ho,Gd,W,Er,Tm,Dy,Tb,Yb,Lu,Tl,Eu,Y,Be,Sm,Ga,Nd,Cr,Pr,Cu,La,U,Th,Bi,In,Zn,Sc,Zr,and Hf.Thirteen out of 53 elements depleted in nodules with depletion degree from low to high for Ca,Ti,Sr,Nb,Cs,Ta,Al,Mg,K,Rb,Si,Li,and Na.The enrichment ratio of Mn and Fe was 29.51(highest)and 3.41,respectively.In highly enriched elements,Mn had a significant positive correlation with Co,Ni,Mo,Ba,Cd,and Pb,whereas a negative correlation with Fe.Fe has a significant positive correlation with P,V,and Sb.(3)There was a significant positive correlation between rare earth elements(REE)and Mn,while there was a negative correlation between Mn and Fe in 0.5-1 mm nodules.A significant negative correlation between Fe and heavy rare earth elements(HREE)and no significant negative correlation with light rare earth elements(LREE)in 1-2 mm nodules were determined.A significant positive correlation between Mn and LREE,and no significant positive correlation with HREE in 1-2 mm Fe-Mn nodules were examined.Both LREE and HREE in soil and Fe-Mn nodules were fractionated,and the degree of fractionation of Fe-Mn nodules was greater than that of soil.A slight negative anomaly of Ce and Eu and a significant negative anomaly in the soil were detected;Ce showed a strong positive anomaly and Eu showed a negative anomaly in Fe-Mn nodules.The distribution patterns of rare earth elements in different pedogenetic soil layers were similar.This indicate soils were derived from a source.(4)Most of iron oxide in Fe-Mn nodules is free iron oxide,and most of free iron oxide is amorphous iron oxide.The content of free iron oxide in Fe-Mn nodules was much higher than that in the soil.The activity of iron in Fe-Mn nodules was stronger than that in the soil.Most of Mn oxides are free manganese in Fe-Mn nodules and most of free manganese oxide is crystalline Mn oxide.Free degree of iron is less than that of Mn in Fe-Mn nodules.The activity of Mn in Fe-Mn nodules was less than that in the soil.