Relation Between Eolian Accumulation and Modern Soil Development in the Southern Part of the Loess Plateau

Key words: 
• micromorphology /
• cultivated soil /
• JYC profile /
• Guanzhong areas

Abstract: A soil profile at the LGT site in the western part of the Guanzhong Basin was studied to illustrate soilforming process and micromorphological features of modern soil. Micromorphology of the thin sections is observed under a petrographic microscope and its image is quantificationally measured by LEICAL Qwin software. Results show that the minerals assemblage of every horizon is very similar, which is mainly composed of Q and Pl. Difference of C/F15μm ratio, mineral content and coarse features is obvious. Coarse grain of the Ap horizon is characterized by higher roundness (1.6361.818), lower aspect ratio (1.8611.909), small size (3541 μm) and some intrusive mass. Shape of coarse grain in BC horizon is characterized by lower roundness (1.8981.982), higher aspect ratio (2.2152.312) and big size (4247μm). BC horizon is characterized by abundant secondarycalcite quantity and slight amount unstable primary minerals such as Cc and Hb and Bi. Pedofeatures mainly consist of clay and calcite and amorphous Fe. Ap horizon is characterized by abundant secondarycarbonate and earthworm excrement and slight amount residual clay. Abundant needleshaped secondary calcite minicrystal is observed in the Ap2 horizon. There are little secondary clay and various secondary calcites in BC horizon. Comparability coefficient, between modern soil and Malan loess L1, is 0.81050.8951 in Ap horizon and 0.90510.9352 in BC horizon, respectively. All the results in this study suggest that Earthcumulic Orthic Anthrosols consists of both upper Ap horizon(040cm), which indicated that loess dung and eolian dust deposition and cultivation occur simultaneously in the process of Ap horizonformation since 2000 years, and lower BC horizon(4075cm), which is aeolian sedimentation in relative aridity period during late Holocene. Abundant needle shaped calcite suggested shortterm stable and dry environment. 