博士 / 國立臺灣大學 / 海洋研究所 / 101 / The Taiwan Island is an active mountain belt formed by the collision of the China continent and Luzon Arcs. Because of active tectonics, high topographic reliefs with steep gradients, frequent typhoons and heavy precipitations, Taiwan is recognized as having particularly high sediment production rates within the small mountainous river systems. In this study, we integrate marine seismic, sub-bottom profiler, and high-resolution bathymetry data together with land well core and log data to investigate the sediment dispersal systems in the areas off southwest and northeast Taiwan. Through seismic facies analyses, sequence stratigraphy studies, physiography analyses and sub-bottom echo image researches, sediment disposal patterns are proposed which help to better understand how the large sedimentary loads were deposited in tectonically active continental margins.
Off Southwest Taiwan, the Gaoping Shelf and Slope are in active convergent tectonic environment, where slope basins are formed by the developments of folds, faults and diapiric intrusions. The complex system of folds, faults, diapirs, slope basins, and submarine canyons could affect sediment dispersal and readjust the morphology of the Gaoping Slope. In this study, we have performed seismic facies analyses to investigate sedimentary processes and depositional environments in the accommodations. Four major seismic facies have been recognized in the Gaoping Slope basins. By comparing different deposition patterns in the slope basins, different stages of basin development during the post-, syn-, and pre- structural phases could be recognized. The thick mud layers beneath the slope basin which are regarded as the source of diapiric intrusions could be related to the Gutingkeng Formation on land Southwest Taiwan. The sedimentary patterns are controlled by the sedimentation rate and structure uplifting (which also means the basin subsidence) rate caused by the convergent and diapiric tectonics in the Gaoping Slope. A“filling-and-spilling” model is suggested to be a basic sedimentary process in this area; however, canyon feeding and mass wasting could be other important processes of sediment dispersal and causing rapid deposition of sediments in the basins.
Off Northeast Taiwan, the Ilan Shelf and Southern Okinawa Trough are in extensional tectonic setting where several normal faults and volcanic activities have also developed. Eight echo types have been recognized from high-resolution sub-bottom profiler images that represent different deposition patterns and interpret shallow sedimentary structures in the Ilan Shelf. Mass transport deposits are widely observed in the outer shelf and the adjacent slope areas of the Southern Okinawa Trough on sub-bottom and seismic profiles. However, mass transport deposits are not observed in the deep sea area of the Southern Okinawa Trough, where sediment dispersal features are mainly controlled by tectonics. Four major sequences have been recognized, and they could be related to different stages of the back-arc extension of the Southern Okinawa Trough. Through sequence stratigraphy analyses of well data onshore and seismic data offshore, a regional unconformity was formed during the last glacial maximum about 20,000 years ago. The estimated amount of deposited sediments since the late Pleistocene is about 1.6 million tons per year on the average. Comparing to the sedimentary budgets of the Lanyang River drainage and the Southern Okinawa Trough, the shelf has trapped 10-20% sediments discharged from the Lanyang River, and the sediments output from the Northeast Taiwan contribute at least 45% sediment depositions in the trough. Mass movement process is suggested to be an important factor for sediments dispersal from the Ilan Shelf to the Southern Okinawa Trough. Submarine mass movement is a rapid sediment transport process which results in extremely high sedimentation rate in the southern end of the Southern Okinawa Trough. Active structures, channel axial incisions, and tidal currents could be the triggers for frequent mass wasting processes in the study area.
Comparing two studied continental margin areas and sediment dispersal systems in other parts of the world, regional structural activities are important factors besides submarine canyons for sediments dispersal. The slope usually represents a bypass zone for most sediment in a sediment dispersal system. However, if slope basins can be developed in the slope area, not only trench and deep sea basins but this kind of structural accommodation spaces in the slope basins could also be another ultimate sink for sediments. Mass movement is another important process for sediments transport from shelf to deep basin, especially when there are no obvious submarine canyons developing in the continental margin areas.
| Identifer | oai:union.ndltd.org:TW/101NTU05279016 |
| Date | January 2013 |
| Creators | Ho-Han Hsu, 許鶴瀚 |
| Contributors | 劉家瑄 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 166 |
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