Weathering and Pedogenic Processes of the Basaltic Soils in Penghu Islands
| Autor: | Chih-Yuan Huang, 黃馳元 |
|---|---|
| Rok vydání: | 2019 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 Penghu Islands are mainly composed of basalts. Basalt weathering is relatively fast when compared with other lithologies. In the previous studies, less research focused on investigating in the Penghu basaltic soils of different weathering degree and characterizing the weathering condition of Penghu basaltic soils via weathering indices. In this study, we took the dating information published by Central Geological Survey (CGS) as reference to sample five soil pedons covering older stratigraphic age (Pedon 1701, 1702), middle stratigraphic age (Pedon 1703) and younger stratigraphic age (Pedon 1704, 1705). The result of particle distribution analysis indicated that the clay illuviation of Pedon 1701, 1702 and 1703 meet the requirements of argillic horizon (Bt) of USDA Soil Taxonomy. Years of evaporation overwhelming precipitation in Penghu Islands made the base saturation percentage (BSP) of all pedons over 35 %. Based on the USDA soil taxonomy, Pedon 1701, 1702 and 1703 were classified as Typic Haplustalfs, and Pedon 1704 and 1705 were classified as Typic Ustorthents. The result of total elemental analysis indicated the high aluminum content of Penghu pedons and the loss of cations under the subsurface during the weathering. Based on the result of total elemental analysis, six weathering indices were selected to characterizing the weathering condition of Penghu pedons, including chemical index of weathering (CIW), chemical index of alteration (CIA), modified weathering potential index (MWPI), Ruxton ratio, bases/alumina (B/A) and bases/R2O3 (B/R). The result indicated that all weathering indices showed the conformity with the morphological characteristics, clay content, activity and crystallinity ratios of free iron oxides, and stratigraphic age, discriminating the highly weathering degree of Pedon 1701, 1702 and relatively lower weathering degree of Pedon 1704, 1705. Because of the poor drainage condition, Pedon 1703 bore too much bases, which led to the outlying outcome in the weathering indices related to base elements. Among all of the selected weathering indices, changes in the CIA value with depth showed the most systematic and steadiest tendency, indicating the enrichment of aluminum and the continuously loss of K, Na, Ca during the process of basalt weathering. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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