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標題: | 臺灣西南海域冷泉環境厭氧甲烷氧化作用下自生性礦物差異之研究 Anaerobic Methane Oxidation and Authigenic Mineral Formations in the Cold Seep Environments, SW Taiwan |
作者: | Yi-Ting Tseng 曾意婷 |
指導教授: | 林曉武(Saulwood Lin) |
關鍵字: | 冷泉,泥火山,黃鐵礦,菱鐵礦,厭氧甲烷氧化作用, cold seep,mud volcano,pyrite,siderite,anaerobic methane oxidation, |
出版年 : | 2016 |
學位: | 碩士 |
摘要: | 冷泉和泥火山為重要氣體移棲的構造。甲烷的移棲造成厭氧甲烷氧化作用的發生,使海水中硫酸鹽還原產生高濃度的硫化氫,最終生成自生性硫化礦物如黃鐵礦物的沉積。熱裂解或是有機物的甲烷生成作用使得環境中富集碳氫類及二氧化碳氣體,最終生成自生性碳酸鹽類礦物如菱鐵礦物的沉積。
本研究主要目的是研究冷泉環境受到硫酸鹽還原作用和厭氧甲烷氧化作用所造成的黃鐵礦物型態差異,並且比較泥火山區之自生性礦物的差異,藉此探討控制這些差異控制因素。研究區域包括泥火山環境燦堯泥火山(TYMV)和冷泉環境四方圈合海脊(4WCR),兩者的位置皆在台灣西南海域活動大陸邊緣,四方圈合海脊位在下部斜坡,而燦堯泥火山位在上部斜坡。分析參數包括間隙水甲烷、硫酸鹽、硫化物、和沉積物總硫、總有機碳和碳酸鹽。以及全沉積物和過篩後之沉積物的XRD(X光繞射)和SEM(掃描式電子顯微鏡)分析。 兩研究區域中皆有快速硫酸根還原之現象,燦堯泥火山所有測站與四方圈合海脊西側測站皆有近表層100-200 cmbsf 處快速硫酸鹽還原反應,且產生高濃度硫化氫。四方圈合海脊的總硫有明顯變化,表現高濃度的測站黃鐵礦物(pyrite)值高達265 μmole/g (C10 243 cmbsf ),而同樣表現快速硫酸根還原的燦堯泥火山各測站並無黃鐵礦物濃度變化。兩環境中自生性礦物種類亦存在極大差異,四方圈合海脊硫酸鹽通量在空間上存在差異,其黃鐵礦物型態相當多元,除一般沉積環境中可觀察到莓狀體黃鐵礦物,亦有次自形面體、正八面、正立方體自形晶。燦堯泥火山沉積物中缺乏硫化礦物的富集,且普遍的在山頂測站表層發現菱鐵礦物。菱鐵礦物的形成需要在甲烷環境(methanic environment)中生成,在表現高濃度硫化氫且高甲烷的泥火山表層發現菱鐵礦物,顯示此環境受氣體、流體和沉積物噴發,影響自生性礦物的產生。 本研究顯示硫酸鹽還原及厭氧甲烷氧化作用反應控制冷泉環境自生性礦物的生成,造成型態的差異。同時,劇烈流體移棲亦可能直接影響環境之自生性礦物的生成,造成自生性礦物種類差異。 Cold seep and mud volcano are two important environments as a result of gas and fluid migration. AOM (anaerobic oxidation of methane) process commonly observed at the seep environment could produce high concentration of sulfide, leading to high concentrations sulfidic condition favoring large quantity of authigenic mineral, e.g. pyrite, formation. Mud volcanos, on the other hand, introduce large quantity of fluid and gasesous materials from deep strata to the surface and may imprint a totally different kind of signal on the environment. The main objectives of this study are to identify differences between cold seep and mud volcano, in particular, types of authigenic minerals formation and processes controlling these differences. Study areas include a mud volcano, the Tsanyao Mud Volcano (TYMV), and a cold seep, the Four Way Closure Ridge (4WCR), both located at active margin offshore southwestern Taiwan, with one at the lower slope, the 4WCR, and another at the upper slope, the TYMV. Analytical parameters include dissolved methane, sulfate, sulfide, and sediment total sulfur, total organic carbon, and carbonate in sediments. XRD (X-ray diffraction) and SEM (scanning electron microscopic) observations were performed on sieved and bulk sediments. Large differences were found between and within these two environments. Rapid sulfate reduction can be observed in shallow depth (100-200 cmbsf) at all sites at TYMV and 4WCR with relatively deeper SMTZ at the east side of 4WCR. High concentrations of pyrite were observed mainly at west and central 4WCR and sites away from the TYMV. Another major difference is the type of authigenic mineral formation found at each environment. At sites with sulfate reduction not involving AOM, framboidal pyrite was found in sediment above the SMTZ in sediments at sites east of 4WCR whereas euhedral octahedral or cubic pyrite were found in sediments where AOM is the predominant process. TYMV is unique that there is very limited pyrite formation even with AOM reaction occur on top, hence little pyrite could be found. With no sulfate in the pore water, siderite formation predominate in the mud volcano system. Furthermore, the discovery of siderite indicates fluid, gas and mud originally from a deep source and were advected upward. This study showed that AOM is a predominant process control variations on the types and forms of authigenic minerals in these two systems. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/76715 |
DOI: | 10.6342/NTU201601717 |
全文授權: | 未授權 |
顯示於系所單位: | 海洋研究所 |
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