HR: 1330h
AN: PP12A-0223    [PDF]
TI: Late Pleistocene environmental fluctuations in Taiwan southwestern plain with constraints of the analyses on organic carbon
AU: * Chiang, H
EM: d91224004@ntu.edu.tw
AF: Dept. of Geosciences, National Taiwan Univ., P.O. Box 13-318, Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: Dept. of Geosciences, National Taiwan Univ., P.O. Box 13-318, Taipei, 106 Taiwan
AB: Taiwan is located at the junction point between the Philippine Sea and Eurasian plate, where the Asian monsoon is supposed as the most important factor in controlling the regional climate. Due to the high subsidence rate caused by westerly moving thrust sheet, sedimentary sequences of late Quaternary overlying on the Tertiary basement in coastal plain are usually over 300 meters. \\ The isotopic composition of organic carbon has been reported to preserve the syn-depositional signals for source identification derived from two major sources, the terrestrial plants and marine organisms. Except for the extreme region, the terrestrial plants can be roughly divided into C$_{3}$ and C$_{4}$ plants in modern world. Since they adopt different photosynthesis processes, each of them shows specific $\delta^{13}$C values. As literatures the $\delta^{13}$C values of organic matters in marine sediments are relatively constant in a local area. On the other hand, the concentrations of total organic carbon (TOC) preserved in sediments can also reflect the experienced paleo-environment. For instance, an anoxic environment, such as a lagoon or marsh will usually preserve high TOC. Consequently, the elemental abundance and corresponding isotopes of organic carbon are wildly used as proxies to retrieve sedimentary environment and vegetation changes. For the purpose of high resolution, i.e., every 3 to 4m, we sampled cores drilled in coastal plain of southwestern Taiwan and conducted carbon isotope analysis to diagnose the detailed environmental changes under the major framework-global change. \\ As our results, TOC values remain in a relatively stable and low level when the corresponding $\delta^{13}$C data indicate marine organic source, while the terrestrial source usually causes undulated TOC. On the other hand, based on the isotopic data measured in the lower part of the core, the study area was inundated by sea-water as a result of the high sea-stand of MIS (marine isotope stage) 5. Subsequently, the climate turned to drier during MIS 2-4, even though there were different durations and extent from north to south. To the beginning of the Holocene transgression the northern study area was still a terrestrial environment dominated by C$_{4}$ plants when the southern was a shallow marine or lagoon. As a whole, our results can conclude that the coastal environments in southwestern Taiwan were consistent with major trend of global changes, but local characteristics were still locally influenced by neotectonics.
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting