| This paper mainly analyzes the micro-moiphological characteristics and their changes of loess-paleosol soil in junwangcun(JWC)and yezhutang(YZT)sections in Hanzhong basin,south of Qinling mountains,and combines with the physical and chemical indicators such as magnetic susceptibility.particle size and chemical elements,compares with the micro-morphological characteristics of loess-paleosol soil in the loess section of the great wall tableland(CCY)in the loess plateau,north of Qinling mountains,studies the soil forming commonness and differences between the two sides of Qinling mountains,and obtains the following understandings:(1)the micromorphological characteristics of loess-paleosol are closely related to the paleoclimatic environment in the process of formation.The decomposition degree of coarse particles is positively re-lated to the warm and humid climate,and the stronger the dissolution and decomposition of coarse particles,the stronger the weathering and pedogenesis,the warmer and humid the indicated climate will be.The pore types and forms are greatly influenced by the water conditions and biological activities in the loess-paleosol formation stage,and there are many pore channels such as root holes,wormholes and the like,and the pore walls are smooth,which indicates that there is sufficient water,biological activities are frequent,and the climate is warm and wet.The types and contents of soil formation are related to the strength of weathered soil.the more clay and iron-manganese concentrated polymer are,the stronger the weathering soil formation will be,and the warmer and wetter the climate will be during its formation.(2)the micro-morphological characteristics of loess-paleosol on the north and south sides of Qinling mountain showed consistent change trend in different sequences.The change trend of average particle size value of coarse particles in each sequence is L1>Lt>L0>S0.compared with loess(L1,L1,L0),the content of coarse particles in ancient soil So is less.Clay mineral content of ancient soil So is higher than that of loess(L1,Lt,L0),and it is impregnated with iron and manganese to a higher degree.pores of ancient soil S0 have a larger transformation intensity by later pedogenesis,while stacked pores and a small number of saccular pores of loess(L1,Lt,L0)have a weaker transformation effect by later pedogenesis.these micro-morphological characteristics of loess-paleosol soil indicate that the weathering pedogenesis degree of ancient soil S0 is stronger than that of loess(L1,Lt,L0).(3)there are obvious differences in micro-morphological charact-eristics of loess-paleosol(coarse grained minerals,pores and soil formations)between the north and south sides of Qinling mountains.The average particle size of coarse particles in Hanzhong basin is obviously larger than that in the loess plateau,with less bone particles and lack of unstable coarse particle minerals such as calcite.Bone particles in loess plateau profile are high in content and complex in mineral composition,secondary calcite can be seen on the edge of pores,and coarse particles are angular.The ancient soil S0 in Hanzhong basin has a large porosity and rich species,with pores and holes dominating.the pore walls are smooth and regular,and the connectivity is good.Loess(L1,Lt,L0)has small pores,uniform spatial distribution and poor connectivity among pores.The pore types in the loess plateau are single,and the saccular pores in the ancient soil S0 are irregular in shape and unevenly distributed in space.Stacking pores of loess(L1,Lt,L0)reflect the pore characteristics of natural dust.the pore walls are rough and serrated,and the connectivity between pores is poor.In Hanzhong basin,the main soil formations are clay minerals and iron-manganese concentrates,etc.the residual clay and deposited clay of ancient soil S0 are very developed,and in addition,more concentrated iron-manganese oxides are found.Loess(L1,Lt,L0)is dominated by eluvial clay,and its iron disseminated degree is relatively weak.Soil formations in the loess plateau are mainly residual clay and secondary calcite,and the residual clay content in the S0 layer of ancient soil is the largest,while acicular microcrystalline calcite is distributed on the edge of pores.Loess(L1,Lt,L0)is dominated by eluvial clay,and there are also a large number of secondary calcite developed.(4)the degree of difference of soil forming strength in different layers of loess-paleosol profiles on the north and south sides of Qinling mountain is not consistent.in Malan loess L1,the difference of coarse particle content and average particle size is relatively small,and the KL1 of coarse particle is 0.68?0.90.The micro morphological features are similar,and clay minerals are mainly residual clays,which indicates that the weathering soil strength in the south of Qinling mountain after aeolian deposit is slightly stronger than that in the loess plateau in the north of Qinling mountain.In the ancient soil S0,the content and particle size of coarse particles in Hanzhong basin are significantly smaller,with Kso= 0.58?0.87 of coarse particles,with significant morp ho logical differences.the soil formation is mainly composed of deposited clay,with little secondary calcite.Soil forming materials of ancient soil S0 in the loess plateau are mainly residual clay and acicular and granular secondary calcite gathered in situ,with a small number of vesicular pores and pore channels,and poor connectivity,which indicates that the soil forming strength of ancient soil S0 in Hanzhong basin is obviously stronger than that of the loess plateau at the same time.(5)the micromorphological changes of JWC profile can well reflect climate change.The variation trend of average particle size of coarse particles in JWC profile in each sequence since the accumulation of Malan loess L1 is coarse ? fine ? coarse,and the variation trend of each sequence in its coarse particle shape is roughly sub-prismatic ? sub-circular ? sub-prismatic,which indicates that the degree of weathering dissolution of coarse particles in Malan loess L1 has changed to weak ?strong? weak since the late Pleistocene.The changing trend of pore types is complex stacked pores,vesicular pores ? pores,channels? vesicular pores,and the changing trend of roughness of pore walls is rough ? smooth ? rough.The change trend of clay mineral content is less ? more ? less,and these micromorphological features indicate that the weathering and pedogenesis change trend of JWC profile is weak ? strong ? weak,indicating that JWC profile has experienced a climate change process of dry-cooling?warm-wet?dry-cooling since late Pleistocene. |
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