博士 / 國立中央大學 / 地球科學學系 / 103 / A series of Cenozoic rifted basins developed in the northern margin of the South China Sea. Tainan Basin is one of these rifted basins near Taiwan lying in the outer margin. We employ reflection seismic data both in the shelf and deep-water areas and boreholes drilled in the shelf to understand the tectonic and sedimentary development, and heat flows in the northern SCS near Taiwan. Temperature measurements carried out on 9 hydrocarbon exploration boreholes together with Bottom Simulating Reflectors (BSRs) from reflection seismic images are used in this study to derive geothermal gradients and heat flows. The method of Horner plot is applied to obtain true formation temperatures from measured bottom-hole temperatures in the boreholes, which are disturbed by drilling processes. Sub-seafloor depths of BSRs are used to calculate sub-bottom temperatures using theoretical pressure/temperature phase boundary that marks the base of gas hydrate stability zone. Our results show that the geothermal gradients and heat flows in the study area range from 28 to 128 ℃/km and 40 to 159 mW/m2, respectively. There is a marked difference for geothermal gradients and heat flows beneath the shelf and slope regions. It is cooler beneath the shelf with an averaged geothermal gradient of 34.5 ℃/km, and heat flow of 62.7 mW/m2, respectively. The continental slope shows a higher averaged geothermal gradient of 56.4 ℃/km, and heat flow of 70.9 mW/m2, respectively. Low heat flow on the shelf is most likely caused by thicker sediments that have accumulated there compared to the thinner sediment thickness beneath the slope.
Four key stratal surfaces (i.e. base of Pleistocene, base of Pliocene, 17 Ma Maximum Flooding Surface (MFS), and break-up unconformity of 30 Ma) and 7 seismic facies (i.e. continuous and parallel layer seismic facies, wavy seismic facies, chaotic seismic facies, U-shape canyon-cut seismic facies, imbricated layer seismic facies, HARPs seismic facies, and extrusive volcanism seismic facies) are recognized from seismic data with ages constrained by borehole stratigraphy drilled in the shelf. A model for the Cenozoic tectonic and sedimentary development in the rifted northern margin of the South China Sea near Taiwan is established. The occurrence of Paleogene fault-bounded grabens/half-grabens topped by break-up unconformity indicates that these rift basins develop on continental crust, attesting that thinned continental crust underlies the deep-water study area, rather than oceanic crust as reported in some literature. High heat-flow values in the continental slope may also result from this thinned continental crust. Extrusive volcanic bodies, of early Miocene age, are buried by thick deep-water sediments showing features of buried seamounts. Fairly continuous stratal surfaces of base Pliocene and base Pleistocene reveals that faulting and volcanic activities almost ceased to be active since middle Miocene. A series of channel cut-and-fills is observed in the late Miocene, Pliocene, and Pleistocene strata beneath or to the south of the modern Formosa Canyon. We name this channel system as Paleo-Formosa Canyon. Two distinct fields of deep-water sediment waves developed since middle Pleistocene are found lying to the west of modern deformation front/Manila Trench, and to the north and south of the Formosa Canyon, respectively.
| Identifer | oai:union.ndltd.org:TW/103NCU05134029 |
| Date | January 2015 |
| Creators | Wei-Zhi Liao, 廖韡智 |
| Contributors | Andrew Tien-Shun Lin, 林殿順 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 87 |
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