Saturday, 15 July 2006

The Profile Development Index (PDI) of the Lateritic rRver Terraces in Central Taiwan.

Heng Tsai1, Wen-Shu Huang1, Zeng-Yei Hseu2, and Zueng-Sang Chen3. (1) Dept of Geography, National Changhua Univ of Education, #1, Chinte Rd,, Changhua, Taiwan, (2) Dept of Environmental Science and Engineering, National Pingtung Univ of Science and Technology, 1 Hseuh-Fu Rd, Nei-Pu, Pingtung, 91201, Taiwan, (3) Dept of Agricultural Chemistry, National Taiwan Univ, 1, Sect 4th, Roosevelt Rd, Taipei, Taiwan

The Quaternary terraced landform is one of the most prominent geomorphic features in respond to the active tectonics in Taiwan. In general, the river terraces with relative height greater than 80 meters above current channel are covered by red soils on the surfaces, and are designated as “lateritic terraces”. Therefore, they are ideal to serve not only as a marker to gauge the surface deformation, but also as a chronosequence to examine the development of red (or lateritic) soils. This study includes the lateritic terraces in the Pakua, Touliu and Chushan areas in central Taiwan. The soils on the surfaces graded from strong brown to yellowish red in color, which in trend roughly agree with the ascending altitude of terraces in each area. A total of 10 representative soil pedons are described and sampled from the terraces. These soils exhibit various degree of laterization, and are classified as Udepts, Udults and Udoxs in Soil Taxonomy. However, the parent materials of the soils depend on sediments from different fluvial systems. The profile development index, PDI, is also calculated by quantifying 6 field properties (rubification, total texture, moist structure, consistence, dry consistence, and clay coatings) of soils. The result agrees with the post-incisive type of soil chronosequence. However, the PDI values is not adequate for the correlation of river terraces which soils were developed from different sources, without help from other data such as Fe oxide content and composition.

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