加积型红土剖面成壤特征及网纹化成因的土壤微形态证据
作者:
作者单位:

1.浙江师范大学地理与环境科学学院;2.浙江师范大学地理与环境科学学院 金华 321004

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基金项目:

国家自然科学基金项目(41572345、41971111) 资助


Micromorphological Evidence on the Pedogenic Characteristics and Reticulated Mechanism of Aggradation Red Earth
Author:
Affiliation:

1.College of Geography and Environmental Science,Zhejiang Normal University;2.College of Geography and Environmental Science,Zhejiang Normal University,Jinhua,321004;3.China

Fund Project:

Supported by the National Natural Science Foundation of China(Nos. 41572345,41971111)

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    摘要:

    亚热带加积型红土很好地记录了中国南方第四纪以来风化特征及其变化趋势,但相应风化强度下古土壤成壤细节仍尚待进一步揭示。本文以庐山东麓海会剖面(L-HH)为研究对象,借助土壤微形态研究方法分析不同风化强度下古土壤成壤特征,并结合粒度、色度、磁化率、地球化学等指标,进一步探讨加积型红土成土环境及网纹机制。结果表明:(1)加积型红土土壤基质以黏土、胶体为主,并具有一定铁质侵染。沿剖面自下而上,胶体含量由70%减少至50%,黏土胶体与碎屑配比由8:2逐渐变化为6.5:3.5,成壤强度呈减弱趋势。(2)土壤孔隙和形成物类型沿剖面的变化差异较好地记录了土壤水分及其干湿变化。网纹红土层以线状大孔道为主,连通性好,铁质迁移活跃,铁锰质胶膜沿孔道分布且多层叠置,部分铁质胶膜有脱色现象,指示水分充足,干湿变化频繁。网纹黄棕色土层大孔道减少,孔洞、囊状孔隙增加,有一定连结性,铁锰胶膜多沿孔隙壁淀积,铁锰质结核也尤为丰富,指示水分减少,干湿变化仍然频繁。黄棕色土层,孔道极少,以面状裂隙、囊状及不规则状孔隙、孔洞为主,连结性差,淀积胶膜多为扩散-团聚型,水分少,铁游离程度降低。(3)土壤孔隙及其发育程度与网纹化程度有较好的对应关系,裂隙产生、加宽、连通是网纹化的物理学基础。(4)剖面土壤微形态特征与粒度、色度、磁化率等环境指标间有良好对应关系,是解读红土形成环境、季风演化和网纹化机制的重要土壤学指标。

    Abstract:

    【Objective】The aggradation red earth sediment is widely distributed on terraces in the middle and lower reaches of the Yangtze River, especially in the piedmont of Lushan Mountain in China. Their sequences haves well recorded the weathering history during Quaternary in South China. Therefore, the objectives of this research were to (1) investigate the micromorphological characteristics of aggradation red earth sequence and (2) reveal the paleosol pedogenic environment.【Method】The research profile was L-HH (29°32 "07.88 "N, 116°04" 19.53"E, H=87 m) at the eastern piedmont of Lushan Mountain. Nine undisturbed samples were collected from the different pedogenic unit and made into thin sections, which were observed by plane polarized (PPL) and crossed polarized light (XPL) using Zeiss Axio Lab. A1 polarizing microscope in the laboratory. A total of 159 bulk samples were collected along with the profile at 5~6cm intervals. Moreover, particle size, chroma, susceptibility and geochemical data of the 159 bulk samples were measured.【Result】L-HH profile can be divided into reticular red soil unit(RRS), reticulated yellowish-brown soil unit(RYB) and yellowish-brown soil unit(YBS) from the bottom up. The soil matrix under Fe-impregnation was mainly composed of clay and colloid, the content of which is up to 50%~70%. The fragments included quartz, plagioclase and muscovite, while the secondary mineral was mostly illite and vermiculite. Also, heavy minerals that were observed included apatite, zircon, rutile and tourmaline. These results suggest in general that the soil units have a moderate-strong degree of chemical weathering. However, there were differences in detail among different units. The voids types of RRS are dominated by large linear channels with good connectivity and smooth wall. Also, the pedological features were mainly composed of coating, ferromanganese nodules, and diffuse concentric rings. Additionally, the illuvial coating developed along the voids wall and formed interbedded layers. Mn-coating was mostly superposed on the Fe-coating, and some pores were filled with the coating. Besides, part of the illuvial Fe-clay coating had a decolorization phenomenon. Thus, the pedogenic environment of RRS was characterized by strong summer monsoon,high soil moisture content, and increased seasonal climate contrast. Furthermore, the voids types of RYB were dominated by vughs, chamber voids and well-connected channels. Fe-Mn features were abundant in the soil matrix. The types of pedological features were rich with Fe masses, ferromanganese nodules and rhizospheric concentric iron-rings scattered in the matrix. The brown-red or grey-black flaky coating was developed repeatedly along the voids wall, and the deposition thickness was increased. Also, the soil moisture decreased, but the alternation between dry and wet was still significant. This, indicated a warm and dry environment. The voids types of YBS were dominated by plane voids, chamber voids, irregular voids, and vughs. Also, the voids’ wall was rough and the channel connection was poor. The pedological features mainly included diffused coating. A thin Fe-illuvial coating was found on some voids wall. During this period, the temperature and moisture conditions became worse. The climate was dry and cool, and the winter monsoon was strengthened. Also, changes of environmental proxies along the profile strongly supported the results of soil micromorphology. From the bottom up, the soil moisture content decreased continuously, and the climate tended to be dry and cool. The micromorphological characteristics support the view that the reticulation process was controlled by iron differentiation. Moreover, the micromorphological characteristics also showed that soil voids and plant roots accelerated the process of reticulation.【Conclusion】The findings in this study demonstrate that there is a significant correspondence between soil micromorphological characteristics and environmental proxies in the L-HH profile. This is an important indicator for interpreting the pedogenic environment of red earth, monsoon evolution signal. and the reticulated mechanism.

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王琳怡,朱丽东,于红梅,李凤全,陈天然,贾 佳,马桢桢,张忠萍,张杭佳.加积型红土剖面成壤特征及网纹化成因的土壤微形态证据[J].土壤学报,2022,59(5). DOI:10.11766/trxb202011240643 WANG Linyi, ZHU Lidong, YU Hongmei, LI Fengquan, CHEN Tianran, JIA Jia, MA Zhenzhen, ZHANG Zhongping, ZHANG Hangjia. Micromorphological Evidence on the Pedogenic Characteristics and Reticulated Mechanism of Aggradation Red Earth[J]. Acta Pedologica Sinica,2022,59(5).

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