Development of cliff-top dune in Fung-chuei-sha, Hengchun Peninsula

• Main Authors: Yi-Chia Wong, 翁翊家
• Other Authors: Lih-Der Ho
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/60559587272186752913

碩士 === 國立高雄師範大學 === 地理學系 === 103 === Fung-Chuei-Sha cliff-top dune is located on a 60-meter-high cliff surface in the Hengchun Peninsula of Taiwan. The development of cliff-top dune is influenced by the factors of sediment source, transportation and deposition, as well as landforms. And these factors is influenced by sea-level change and conversion of wet condition and wind speed .Therefore, cliff-top dune preserves information of paleo-environment events. However, it is still unclear that when the eolian sediments start to deposit on the Fung-Chuei-Sa cliff top, and what factors may influence the evolution of the cliff-top dune. This study aims to investigate the evolution process of the Fung-Chuei-Sha cliff-top dune by analyzing grain size, CaCO3 concentration, land snail species and 14C dates of land snail shell. The results show three phases of aeolian sand accumulation in Fung-Chuei-Sha cliff-top dune. The Phase I stared at 2800 yr BP and ended at 2100 yr BP. The wet environment may cause the sediment accumulated below the cliff. The cliff-top dune started to develop at 1500 yr BP in Phase II.In this phase, cliff-top dune accumulated 3.1-meter-thick sediment (260-570cm). Dune deposits in a rate of 1.55 cm/yr. The paleoclimate date indicte that the environment is dry and the northeast monsoon is more strongly during 1500-1300 yr BP. It blowed the old coastal dune deposits up to the cliff top and induced the 14C age reverse phenomenon. The aeolian deposition began to stabilize because of the wetter environment in the end of the Phase II. At the same time, the stability of dune formed the silt and clay layer (240-260 cm). The layer cemented by CaCO3 (320-400 cm) may indicate the old groundwater table. Phase III stared between 1500 yr BP and 1300 yr BP, and to the precent. A 2.4-meter-thick eolian deposit (0-240cm) was accumulated in a rate of 0.18 cm/yr. Four kinds of land snail shells, Cyclophorus formosensis, Hemiphaedusa similaris, Platyrhaphe swinhoei, Odontartemon heudei, which prefer to live in a relatively humid environment, were commonly observed in this deposit section, but not in the begining of Phase II deposition. The result indicates that the wet environment may cause a slower aeolian deposition rate at Phase III. A period of relative stability stared at 1000 yr BP and ended at 500 yr BP because of the wetter environment.Dune still accumulate until now after 500 yr BP.The aeolian deposition generally happened in East Asian beach during 3000-2000 yr BP, 1500-1300 yr BP and 500 yr BP. The paleoclimate dates indicate that northeast monsoon was increasing during these three periods. In this study, we surmise that the evolution of beach dune has relationship with the increasing of northeast monsoon