AMS 14C dating and geochemical study on tree-ring and Taal Lake sediments in Central Philippines

• Main Authors: Min-Shuo Liou, 劉閔碩
• Other Authors: Hon-Chun Li
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/6pvqa3

碩士 === 國立臺灣大學 === 地質科學研究所 === 106 === Taal Volcano is an active volcano in the Philippines and is one of the 16 monitored volcanoes by the Global Volcanism Network in the world. Historic documents show that the volcanic eruption of Taal has been more than 30 times since 1572 C.E.. In this study, we attempt to find out geochemical proxies of volcanic eruption and to reconstruct volcanic activities recorded in the Taal Lake sediments during the past 60 years. In order to demonstrate the nuclear bomb 14C curve in the studying area, we attempt to reconstruct the nuclear bomb 14C curve in nearby tree rings and Taal Lake sediments. The AMS 14C dating on tree rings of Tectona grandis taken near the Taal Lake in 2011 and a 120-cm long gravity core (Core TLS-2) retrieved from 15-m water depth of Taal Lake indicates that: 1) The nuclear bomb 14C pulse recorded in the Tectona grandis growth rings is the same as other published tree-ring records in the tropical regions. 2) The 14C values of the holocellulose were higher than these of whole wood from the same rings when the atmospheric bomb 14C was rising (1956-65 C.E.); but the situation was reversed when the atmospheric bomb 14C was dropping quickly after 1965 C.E.. This is because the holocellulose in the tree was formed in the early season and the whole wood was developed in the entire year. 3) By comparing the 14C curve of the tree ring with the atmospheric bomb 14C curve, we found a fake ring and three missing rings in the tree ring counting, which helped the tree ring chronology. 4) AMS 14C dates on plant remains at different layers of the core show that the nuclear bomb 14C pulse was recorded in the sediments of Core TLS-2, but the magnitude of 14C values is lower than that of the tree-ring record due to mixing and dilution effects. 5) The comparison of the bomb 14C curves between the tree ring record and a Taal Lake sediment core TLS-2 allows us to build up the chronology of the 120-cm long Core TLS-2 which has an average sedimentation rate of 2.04 cm/yr. Investigations on the water and modern sediment samples of Taal Lake show that: 1) Fe, Mn, Cu and Zn may be used as indicators of volcanic activity. 2) Isotopic composition of Taal Lake bias from MWL indicates mixing of isotopically heavy geothermal fluid and isotopically light surface input. 3) For Core TLS-2, the δ18O and δ13C of Total Inorganic Carbon (TIC) co-vary in general. 4) The anomalies of high concentrations of Fe, Mn, Cu, K, Ba in the acid-leachable phase around 1991-1994 may correspond to high activity of Taal Volcano during this interval. These proxies may be considered as indicators of geochemically monitoring volcanic activity for long-term prediction.