Episodic erosion of the Eastern Coastal Range since 13 ka：evidence from reworked nannofossils in the core sediments of the Hualien Plain

• Main Authors: Kai-Zheng Du, 杜開正
• Other Authors: Ping-Mei Liew
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/35057594949560102743

碩士 === 國立臺灣大學 === 地質科學研究所 === 96 === The erosion of mountain belt is a major topic in studying Earth surface processes, which can be resulted from tectonic uplift or climate change and is often discussed in this tectonic active island. Basin deposits in front of mountain belt provide sedimentary sequence for studying mountain erosion. The sediments in the Longitudinal Valley of Eastern Taiwan come from both Eastern Coastal Range and Central Range. It is difficult to discriminate their sources since both Ranges export slate detritus into the sediments. These several years, many cores were drilled from the Hualien Plain by Central Geology Survey in Taiwan and some reworked nannofossils in the core sediments were found. This study further discerned that the reworked nannofossils were derived from the strata of Coastal Range. The reworked nannofossils are thus taken as an indicator for studying erosion history of the Eastern Coastal Range since late glacial. In order to measure the abundance of reworked nannofossils, analysis in this study was made quantitatively both in the four core sediments of Hualien Plain (Beipu, Minyi,Tsichi and Kuanhua) and the present muddy sediments of the Hualien River. Totally 221 samples were analyzed. The preliminary conclusions are: 1. The Hualien River flooded further north than present, to Beipu area, during late Glacial and early Holocene. 2. After typhoon the abundance of reworked nannofossils in muddy sediments of Hualien River still increased even though Central Range also provides lots of sediments to dilute them. This may indicate the close relationship between erosion rate and lithology. 3. A remarkable erosion- event occurred in the Eastern Coastal Range during early Holocene (about 10.4 ka) which was evidenced by abundant reworked nannofossils in core sediments of Beipu and Minyi of Hualien Plain.