The soil development and the geomorphic implications to the marine terraces of Hengchun Peninsula, Taiwan

• Main Authors: Huang, Wen Shu, 黃文樹
• Other Authors: Tsai, Heng
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/97255091046668463406

博士 === 國立彰化師範大學 === 地理學系 === 98 === The marine terraces of the Hengchun Peninsula, located in the southmost tip of the Central Range, were the excellent sites to exam the pedogenetic process and the geomorphic correlations for landform evolution and neo-tectonic activities. But the geomorphic correlations between researchers have been in controversy because of the subtle geomorphic features. This study provided new evidences based on pedogenic characteristics of the soils over the marine terraces to gauge the soil-geomorphic processes as well as re-consider the correlations of the marine terraces. Five soils, labeled as KT-2, KT-3a, KT-3b, KT-4 and KT-5, and another six, labeled as HT-1a, HT-1b, HT-1c, HT-1d, HT-2a and HT-2b, were sampled on the marine terraces in Kengting area and West Table land respectively. Moreover, seven reef-limestones, one eolian dune sand and one beach sands were also sampled for the further determination of the minerals. The pedo-stratigraphic morphologies, unreasonable required amounts of reef-limestone for insoluble residue, sand-size fraction minerals of soils as well as limestone reveal that the soils over the marine terraces derived from the fluvial deposits, eolian or beach sands, which none-calcerous minerals of them were all inland source, instead of reef-limestone. The soils on the terraces with high altitudes, such as KT-2, KT-3a, KT-3b, HT-1a, HT-1b, HT-1c and HT-1d, were identified as higher genetic degrees with morphologies of clay coatings, argillic horizon, low CEC/caly, higher Fed and kaolinite contents. These soils were classified as Ultisols based on the Soil Taxonomy but the genetic degree of the KT-2 soil was slight higher than others. In contrast, the soils on the lower terraces, showing none or less genetic morphologies, were classified as Inceptisols and Entisols in the Soil Taxonomy. Therefore, a post-incisive chronosequence was formed because the pedogenic degree increased with the terrace altitudes (age). Taking into consideration of the soil parent materials and the pedogenic morphologies, two soil-geomorphic models were respectively proposed to reveal the landform surface process after the terrace uplifting in the Kengting area and the West Tableland. In Kengting area, at the first stage, the sea level was the highest and the wave-platform of the reef was formed. The sea level started to descend and fluvial deposits from inland covered on the wave-platform at the second stage. Then, the wave-platform uplifted and departed from the sea level at the third stage, whereas the fluvial deposit experienced a long period of weathering to form Ultisols. At the last stage, eolian dune sands overlying on the part of the soils were caused by the strong northeast monsoon in modern time. In the West Tableland, the barrier reef and the lagoon were formed while the highest sea level at first. At the second stage, the sea level descended whereas the barrier reef were eroded by wave to form a wave-platform and rivers moved deposits into the lagoon. The wave-platform was covered thick eolian sands that originated in fluvial deposits or the lagoon-shore sands. At the third stage, the wave-platform was abandoned for the sea level and inclined to the east due to the tectonic uplifting. The sand deposits on the wave-platform had been weathered and formed as the Ultisols. According to the indicators of the soil properties, such as horizon index (HI), weighted profile development index (WPDI), clay, Fed, CEC/clay, and ECEC/clay, all soils on marine terraces in the Hengchun Peninsula were correlated as three levels: 1st was the KT-2 soil; 2nd was the KT-3a, KT-3b, HT-1a, HT-1b, HT-1c and HT-1d soils; 3rd was the KT-4, HT-2a, HT-2b, KT-5 soils. Furthermore, in convenience, the soils labels would be representative of the terraces that the soils belong to. Referring to pedogenic correlations and geomorphic features, like terrace altitudes, the marine terraces in the Hengchun Peninsula were correlated as five levels: KT-2 was the second level, whereas KT-3a, KT-3b, HT-1a, HT-1b, HT-1c and HT-1d were the third level. KT-4, HT-2a, HT-2b were the fourth level and KT-5 was the latest. The result of the pedogenic correlation conformed to the dating of the reef limestone. KT-2, KT-3a, KT-3b, HT-1a, HT-1b, HT-1c and HT-1d were abandoned at the last inter-glacier about 135-80 ky, but the age of the KT-2 with higher pedogenic degree was earlier than other soils. The KT-4, HT-2a and HT-2b formed after 60 ky.