花岗岩上发育的亚热带红土岩石磁学特征

本文对发育于花岗岩上的两个亚热带红土剖面进行了系统的岩石磁学研究,测试了磁化率、频率磁化率、等温剩磁、非磁滞剩磁、磁滞回线等常温磁学参数,选取代表性样品进行了高低温岩石磁学分析,拟探讨亚热带红土磁性矿物的特征及湿热环境下土壤中磁性矿物的转化规律。实验结果表明:亚热带红土的强磁性矿物为磁铁矿、磁赤铁矿;弱磁性矿物为赤铁矿和针铁矿,滞水土层中含有纤铁矿。花岗岩具有较强的磁性,在其上发育的红土也因此具有较强的磁性。花岗岩中的亚铁磁性矿物的磁畴以多畴占主导地位,随着风化强度的增强,逐渐形成较细粒的超顺磁与单畴磁性矿物。亚热带红土中的磁赤铁矿与位于半干旱区黄土高原成土作用形成的磁赤铁矿存在着磁学性质上的差异,表现为具有更高的居里点(约600℃和640℃),可能说明亚热带红土中的磁赤铁矿粒径更粗。两个剖面在磁学性质上存在着明显的差异,泉州剖面磁性矿物以磁铁矿为主,磁化率最高可达1823×10^(-8)m^3/kg,平均值为1033.1×10^(-8)m^3/kg,具有较低的剩磁矫顽力;福州剖面磁性矿物以磁铁矿和部分热稳定磁赤铁矿为主,磁化率最高为385.73×10^(-8)m^3/kg,平均值为91.5×10^(-8)m^3/kg。基于磁学参数分析,认为母质与后期成土作用共同造成了两个剖面的磁学性质差异,但后者起主导作用。磁化率在两个剖面中,均随着深度减小而减小,与温带地区表层土磁化率增强有很大区别。湿热环境条件下,强磁性矿物溶解或转化为弱磁性矿物的程度主导剖面磁化率变化。

亚热带地区花岗岩风化壳上发育红土的磁性矿物转化机制——基于非磁学指标和岩石磁学的综合分析

选取亚热带地区发育于花岗岩风化壳上的两个典型红土剖面（福州剖面和泉州剖面）作为研究对象，在前期系统岩石磁学研究的基础上，结合常量地球化学元素、色度、粒度指标，分析磁学特征与环境条件的内在联系，重点探讨亚热带湿热气候条件下红土中磁性矿物转化途径及机制。结果显示：1）两个剖面硅（SiO2）、铝（Al2O3）、铁（Fe2O3）等常量地球化学元素含量及其随剖面深度变化规律基本一致；衡量风化强度的化学蚀变指数（CIA）、风化淋溶指数（ba指数）以及元素比率（如硅铝率和硅铝铁率）在数值上非常相近。常量地球化学参数表明两个剖面土壤均处于脱硅富铝化的成土阶段。2）两个剖面红度和黄度值差异较大，表明福州剖面土壤中赤铁矿和针铁矿含量相对较高；色度参数在两个剖面中随深度变化规律具有较好的一致性。3）两个剖面粒径均随风化程度增强而变细，强风化层位粘粒含量最高；相较于泉州剖面，福州剖面粒度更细。综合分析野外土壤发生特征及上述参数，认为福州红土剖面由于成土时间较长，因此经历了更强的后期风化作用。在此基础上，分析土壤磁性转化影响因素及转化机制，得出如下结论：1）亚热带地区湿热的气候条件是磁性矿物总体特征变化的主导因素；2）土壤母质和成土时间是亚热带地区不同红土剖面磁性矿物特征差异的主控因子；3）亚热带地区土壤磁性矿物转化途径不同于温带地区：湿热气候条件对原生磁性矿物改造作用更为明显，并且影响次生磁性矿物的赋存形式。

Impacts of Choerospondias axillaris Growth on Acidity of Udic Ferrosols in Subtropical China

Changes in acidity of Udic Ferrosols, caused by growth of Choerospondias axillaris (Roxb.) Burtt et Hill, in comparison to wild grass, were investigated for pH distribution in the soil profile, exchangeable acidity, and cation status in the soil leachate of a simulated leaching experiment. Soils were sampled in profiles at 5 cm intervals to a depth of 100 cm. In the 15-60 cm layer the soils with 10-year old C. axillaris had significantly lower pH (P < 0.05), with the largest difference being 0.41; and in…

Fertility Restoration of Red Soils in Low-Hilly Region of Middle Subtropical China

There are about 1.27 million ha of upland red soils derived from Quaternary red clay facing the degradation in the low-hilly region of the middle subtropical China. From the aspects of chemistry, physics and microbiology, the processes of soil fertility restoration in the surface layer (0～20 cm) under three types of land use patterns (i.e. citrus orchard, tea garden and upland) in two provinces were studied in this work. Results showed that the reclamation of eroded waste land improved most of soil properties. Soil organic matter, total N and P, available P and K, and exchangeable Ca and Mg increased, but soil total K and exchangeable Al decreased. Soil PH decreased by 0.5 unit in the pure tea plantation for 20 years. Soil reclamation increased the percentage of soil microaggregates (<0.25 mm), especially those with a diameter of 0.02～0.002 mm. Soil total porosity increased in the cultivated lands with the increase of soil aeration and capillary porosity. The number of soil microorganisms increased with reclamation caused mainly by the huge increase of the total amount of bacteria. With the cultivation, the activity of soil urease and acid phosphatase increased, but that of invertase dropped.

Preliminary Evaluation of Some Engineering Properties of Laterite as Foundation and Construction Materials in Muglad Basin in Sudan

This paper reports and evaluates the subsurface investigations of lateritic soil in Muglad Basin. Lateritic soil is described as highly weathered and altered residual/transported soil formed by the in-situ weathering and/or decomposition of rocks in the tropical and sub-tropical regions with hot, humid climatic conditions. The field works include excavation of test pits, drilling of boreholes and performing of SRT （standard penetration test）. The engineering properties of soil such as sieve analysis, consistency, compaction test, CBR （California bearing ratio） test are deduced in the laboratory. Lateritic soil is also evaluated to be used as foundation and construction materials. Concretionary lateritic soil is valuable road pavement materials, widely used in the tropics as sub-base, base material and for gravel roads. The term laterite, however, has tended to be indiscriminately applied in tropical highway engineering to any red soil. Lateritic soils in this study area were classified as reddish brown, medium dense to very dense, clayey silty sand with noodles of quartz and gravels. According to laboratory test, the lateritic soil was found to be good as construction materials, and can be used for embankment purposes; on the other hand, blending such materials with gravels can improve the low CBR values.