碩士 / 國立臺灣海洋大學 / 地球科學研究所 / 107 / The Yung-An Ridge is an elongated submarine ridge, which is approximately 24 km long and 7 km wide. The Yung-An Ridge is located on the eastern side of the deformation front offshore southwestern Taiwan On the sea floor near the Yung-An Ridge, methane gas releases visibly from the seafloor, and many methane-related carbonate reefs grow have been well observed, based on investigations supported by the Geothermal and Gas Hydrate program of the National Energy Program Phase II (NEP II). This study used four giant piston cores, MD103274, MD103275, MD103276, and MD103277 retrieved from the Yung-An Ridge by the Central Geological Survey, and aims to establish the lithostratigraphies and chronostratigraphies of the cores. The core lengths vary between 22 and 35 meters and were located across approximately 6.5 km at the Yung-An Ridge. This study used core description data to locate the void and soupy layers for indicating the in situ gas hydrate formation depths, and by combining the depths of coarse-grained sediment layers, magnetic susceptibility, the depths of Sulfate-Methane Interface (SMI) to establish the lithostratigraphic frameworks of the four cores. The results indicate that the void/soupy layers are mostly distributed in the depths of reduced conditions of the four cores, suggesting effects of gas hydrate formation. Furthermore, In this study, two samples with planktic foraminifer fossil shells (>10 mg, mixed Globigerinoides ruber and Globigerinoides sacculifer) have been picked up from the top and bottom of each core. sampled the top and bottom of each core for AMS 14C dating. The eight new AMS 14C dating, combined with the dating results from previous studies, were used to establish age models and chronostratigraphies of the four cores. The results indicate that the age of the four cores range from recent to 60,000 years BP, which corresponding to Marine Isotope Stage (MIS) 1 to 4. The average sedimentation rates of the four cores range from 178 to 68 cm/kyr, suggesting a huge supply of terrestrial sediments transported possibly from Gaoping River and Penghu Channel. This study shows that the in situ gas hydrate formations have been much more enriched in glacial / sea level lowering conditions, especially from the early MIS 1, MIS 2, and early MIS 3 to MIS 4. This study concludes that the more abundant in situ gas hydrate formations at the Yung-An Ridge could be attributed to high terrestrial sediment fluxes from Gaoping River and Penghu Channel during sea level lowering, that favor more organic matters transported, buried, and preserved in the sediments.
| Identifer | oai:union.ndltd.org:TW/107NTOU5135006 |
| Date | January 2019 |
| Creators | Cheng, Ya-Yun, 鄭雅云 |
| Contributors | Chen, Min-Te, 陳明德 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 51 |
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