| Summary: | 碩士 === 國立臺灣海洋大學 === 應用地球科學研究所 === 99 === This core was taken from the Da-Hu Lake (DH-7B) Ilan, Taiwan for particle size, mineral, and element content analyses. The study provides an explanation of core data found in DH-7B through comparison of mineral and geochemical content by geochemical proxy and sediment source to explore the paleoclimatic conditions and paleoenvironmental change in Ilan.
The sedimentary core provides a 7,500 year record of the Da-Hu Lake including: Lan-Yang River flooding between 6100~5100 yr B.P. and 4300~4800 yr B.P., frequent typhoon activity leading to increased precipitation between 1650~1250 yr B.P., and wetter periods between 1100~400 yr B.P. in Ilan that may indicate strengthening in both typhoon and winter monsoon activity. Quartz records indicate that the eastern monsoon had a profound effect in the Ilan region during the little ice age 400 years ago.
Based on the upper reaches of the Lang-Yang River having extensive fan-terracing, as well as pollen sequences, meteorological data, particle size analysis, and chemical indicators in the Da-Hu and Mei-Hwa Lake, it is speculated that for the period 2100 ~ 1500 yr B.P. large-scale river deposits occurred in Da-Hu lake because of slope instability caused by tectonic activity. In addition, a maximum amount of Alnus pollen also occurred in 1600yr B.P. This pollen could have been carried along with other colluvium down the Lang-Yang River as a result of torrential rains from monsoon and typhoon activity. Presently the core records fdisplay the Ilan region experienced successional catastrophes during 2100~1300 yr BP. It also proves that archeological hiatus occurred during 2400~1300 yr B.P.
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