碩士 / 國立臺灣大學 / 地質科學研究所 / 106 / In Taiwan, the Philippine Sea Plate collided and overridden on the Eurasian Plate along the Longitudinal Valley Fault (LVF). The southern segment of LVF consists of three faults─Chihshang fault, Lichi fault and Luyeh fault, which behave as creeping thrust fault. On the hanging wall of these active faults, the well-preserved and extensive emergent marine terraces and coral reefs along the Huatung coast are the result of sea level fluctuations superimposed on tectonic uplift since the postglacial period.
In this study, we collected previous research of sea level oscillations around Taiwan and reconstructed sea level curve during the past 20,000 yrs. Between 16 and 7 ka, sea level rose from ca. -110 m to ca. 0 m at a rate of 13 mm/yr, and then became stable after 7 ka. At the same time, the average tectonic uplift rate remained quite stable in the study area, ranging from 3-7 mm/yr to 9-13 mm/yr in Sanxiantai-Dulan and Fushan-Fukang, respectively.
The interaction between sea level fluctuation and tectonic uplift, also known as relative sea level change (RSL), resulted in the environment change from a relative transgression to a relative regression, and was recorded completely in the depositional sequence in Dulan area. (1) ~17-16 ka: The rate of eustatic sea level rise was slightly lower than the crustal uplift rate. The bedrock of Paliwan Formation formed a wave-cut platform. (2) ~16-8 ka: RSL rose about 50 m, the nearshore to offshore deposits uncomformably overlaid on the wave-cut platform. As RSL rose, the platform extended landward and sedimentary accommodation space increased which resulted in the deposition of thick-bedded marine deposits. (3) ~8-7 ka: The similar rate of tectonic uplift and eustatic sea level change caused the marine terrace formed in this period broad. (4) After ~7 ka: The crustal uplift rate surpassed eustatic sea-level rise rate which led to form a series of Holocene marine terraces. Due to fast and active crustal uplift, time for terrace formation is much shorter and accommodation space is much smaller. Holocene marine terraces display a characteristic of narrow terrace surface and thin beach-face deposits.
Although RSL plays an important role in the evolution of terrace formation, the relationship between Holocene marine terraces in Huatung coast and RSL seems not related. The width of marine terraces may be narrower when RSL falls faster, but there is not so obvious in the study area because of coastline recession which is affected by lithology and amount of sediment supply, thus the rate of retreating coastline changes with regions. Coastline recession of a subsequent sea cliff into the landmass might narrow the width of higher marine terraces even remove it.
Lower terraces are uplift by coseismic deformation and interseismic creeping, and multiple steps of small terrace could be merged together because of retreating coastline, displaying as higher sea cliff. The characteristic of deformation deduced from marine terraces denote that heights of sea cliff in Huatung coast are accumulated from several coseismic uplift and interseismic creeping uplift. In conclusion, occurrence of marine terrace is controlled by several factors, such as lithological character, oscillation of global sea level, crustal uplift rate and coastline retreat. These factors altogether formed various Holocene marine terraces.
| Identifer | oai:union.ndltd.org:TW/106NTU05138007 |
| Date | January 2018 |
| Creators | Szu-Ting Chen, 陳思婷 |
| Contributors | Wen-Shan Chen, 陳文山 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 163 |
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