台灣西南海域指標脊之天然氣水合物賦存區的構造特徵

Structural features of the potential gas hydrate area in the Pointer Ridge off southwest Taiwan

王雪芬(Hsueh-fen Wang)

指導教授 ： 許樹坤

國立中央大學/地球科學學院/地球科學系/碩士(2015年)

摘要

台灣西南海域位於南中國海北側大陸邊緣與馬尼拉增積岩體（accretionary wedge）斜向聚合的區域。本研究區域─指標海脊（The Pointer Ridge, PR）座落於變形前緣以西，南中國海北緣被動性大陸斜坡處。此區域之構造特徵主要為地壘與地塹構造（horst-and-graben structures），在大陸斜坡上，因海底切蝕作用形成了許多的海底峽谷與海底山脊。根據地物、地化與地熱的研究，台灣西南海域蘊含著豐富的天然氣水合物（gas hydrate）。因此，本研究主要的目的為探討指標海脊近海床地層與天然氣水合物相關構造特徵之調查。
本研究運用高解析側掃聲納儀（Side-Scan Sonar）、底質剖面儀（Sub-Bottom Profiler）、科學漁探儀（Echo Sounder System）與多頻道反射震測資料（Multi-Channel Seismic）等資料調查此區。從反射震測資料中發現大量的海底仿擬反射（Bottom Simulating Reflector, BSR）存在。根據資料整合的結果顯示，在研究區域中發現噴氣構造、麻坑構造、自生碳酸鹽礁以及聲波透明帶等天然氣水合物相關得特徵，這些與天然氣水合物相關之構造特徵主要集中在指標海脊的高區，海底仿擬反射（Bottom Simulating Reflector, BSR）厚度變化最大的地方。綜合上述的資料，可以間接推測本研究區域有天然氣水合物之賦存。

關鍵字

天然氣水合物 ； 西南海域 ； 自生碳酸鹽礁 ； 麻坑 ； 海底仿擬反射

並列摘要

The offshore area of the southwest Taiwan is located in the oblique convergence zone between the northern continental margin of South China Sea and the Manila accretionary wedge. To the west of the deformation front offshore southwestern Taiwan, the Pointer Ridge is located in the South China Sea passive continental margin. The continental margin is compose of extensional horst-and-graben structures. There are numerous submarine channels and linear ridge, formed due to the submarine erosion across the continental slope region. According to geophysical research off SW Taiwan, potential gas hydrate may exist. In this study, our purpose is to study the relationship between the near-seafloor structures of the Pointer Ridge and the gas hydrate formation off SW Taiwan.
The data used in this study include side-scan sonar（SSS）, sub-bottom profiler（SBP）, echo sounder system（EK60）and the multi-channel reflection seismic（MCS）data. Our results show that pockmarks and gas seepage structures mainly appear in the place where the gradient of the BSR thickness is maximum. Those sites also show authigenic carbonate signature in the sub-bottom profiler. We also observe several folds and faults structures in this extensional background; however, these compressional features need further studies.

參考文獻

Chi, W. C., Reed, D. L., Liu, C. S., & Lundberg, N. (1998). Distribution of the bottom-simulating reflector in the offshore Taiwan collision zone. Terr. Atmos. Ocean. Sci, 9(4), 779-794.

Holvland, M. H., & Judd, A. G. (1988). Seabed Pockmarks and Seepages: Impact on Geology. Biology and the Marine Environment, Graham and Trotman, London.

Hovland, M., & Curzi, P. V. (1989). Gas seepage and assumed mud diapirism in the Italian central Adriatic Sea. Marine and Petroleum Geology, 6(2), 161-169.

Hovland, M. (2002). On the self-sealing nature of marine seeps. Continental Shelf Research, 22(16), 2387-2394.

Hovland, M., Gardner, J. V., & Judd, A. G. (2002). The significance of pockmarks to understanding fluid flow processes and geohazards. Geofluids, 2(2), 127-136.