本文關(guān)鍵詞：中挪威海Nyegga麻坑區(qū)冷泉碳酸鹽巖的研究　出處：《中國科學(xué)院研究生院(廣州地球化學(xué)研究所)》2015年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： Nyegga麻坑區(qū) 冷泉碳酸鹽巖 沉積巖石學(xué) 同位素地球化學(xué) U-Th定年 甲烷滲漏活動(dòng)

【摘要】：冷泉碳酸鹽巖和化學(xué)自養(yǎng)貝殼忠實(shí)地記錄了過去富甲烷冷泉流體滲漏活動(dòng)的歷史,同時(shí)也反映了冷泉活動(dòng)區(qū)的古環(huán)境特征。本文以挪威海Storegga海底滑坡北緣的Nyegga麻坑區(qū)CN03、Tobic、Do Do和G11四個(gè)麻坑的冷泉碳酸鹽巖和生物雙殼為研究對(duì)象,開展了系統(tǒng)的巖石學(xué)、礦物學(xué)、同位素地球化學(xué)、U-Th研究,來認(rèn)識(shí)該麻坑區(qū)冷泉碳酸鹽巖的成巖環(huán)境、過去富甲烷滲漏流體的組成、甲烷來源以及演化特征、確定甲烷釋放的年代,并探水合物分解與Storegga海底滑坡的關(guān)系。研究結(jié)果顯示,Nyegga麻坑區(qū)碳酸鹽巖孔洞和裂隙非常發(fā)育,部分碳酸鹽巖膠結(jié)有大量的化學(xué)自養(yǎng)貝殼。碳酸鹽巖中石英、長石、粘土等碎屑含量較高,表明冷泉碳酸鹽巖最初形成于海底淺層沉積物孔隙中。顯微鏡下,碳酸鹽礦物以泥晶高鎂方解石和針狀文石為主導(dǎo),伴有極少量的白云石。草莓狀黃鐵礦和球粒分布廣泛,揭示了碳酸鹽巖形成時(shí)的還原環(huán)境及微生物的參與作用。碳酸鹽巖的δ13C值為-58.67~-47.46‰PDB,清楚地表明冷泉碳酸鹽巖經(jīng)甲烷厭氧氧化過程而形成,且微生物成因的甲烷為其主導(dǎo)碳源。生物殼的δ13C值為-3.8~-2.7‰PDB,指示其碳源為正常海水DIC。冷泉碳酸鹽巖的87Sr/86Sr比值為0.70913~0.70918,指示碳酸鹽巖成巖流體主要受底層海水影響,而非深層流體,這也從另一方面證實(shí)了形成冷泉碳酸鹽巖的甲烷為微生物成因的。通過鈾系不平衡U-Th測年法測定了部分冷泉碳酸鹽巖的年齡。定年初步結(jié)果顯示,該麻坑區(qū)冷泉碳酸鹽巖形成于18.5-12.3 ka,即末次冰盛期以來的不同年代,反映了Nyegga麻坑區(qū)的甲烷滲漏活動(dòng)為間歇式的,經(jīng)歷了多次活躍和休眠。通過碳酸鹽巖和生物殼的氧同位素重建的古流體δ18O值顯示,形成于末次冰盛期的冷泉碳酸鹽巖與古海水的氧同位素處于平衡態(tài),滲漏流體的甲烷很可能來源于較深部的水合物分解釋放的甲烷,水合物分解釋放的重氧同位素對(duì)在淺層生成的冷泉碳酸鹽巖的氧同位素組成影響不大。而形成于全新世的顯示有稍偏重(~+0.7‰)的18O來源,推測其可能主要是由構(gòu)造活動(dòng)等其它因素導(dǎo)致的淺層水合物分解而來。綜合研究結(jié)果,認(rèn)為Nyegga麻坑區(qū)的甲烷滲漏活動(dòng)自18 ka以來都很活躍,比最近的滑坡事件8.1 ka要早很多,因此初步推測該區(qū)水合物分解導(dǎo)致的甲烷滲漏可能是該區(qū)海底滑坡的誘導(dǎo)因素之一。
[Abstract]:Cold seep carbonate and chemoautotrophy shells to record the past methane rich cold fluid seepage activity history, but also reflects the ancient environment of the active region. Based on the cold spring and Weihai Storegga submarine landslides along the northern margin of the Nyegga pit area CN03, Tobic, Do, Do and biological seep carbonates and G11 four pockmark double shell as the research object, carry out the system of petrology, mineralogy, isotope geochemistry, U-Th, diagenetic environment of the pit area of cold seep carbonates, composed of methane rich fluid leakage past the methane source and evolution characteristics, determine the age of methane emissions, and to explore the relationship between hydrate decomposition and Storegga submarine landslide the results show that the Nyegga carbonate pit area porosity and crack development, part of carbonate cementation has a large number of chemoautotrophy shells. Quartz carbonate, feldspar, clay, etc. Detrital content is high, that cold seep carbonates originally formed in sediments of shallow pore. Under the microscope, micritic carbonate minerals with high magnesium calcite and aragonite needle is dominant, with very few dolomite. Framboid pyrite and chondrules are widely distributed, reveals a reductive environment and microbial carbonate formation in the the role of 13C in carbonate rocks. The delta value of -58.67~-47.46% PDB, clearly shows that the anaerobic oxidation of methane seep carbonates in the process of forming, and biogenic methane as the main carbon source. 8 13C biological shell value is -3.8~ -2.7% PDB, indicating the carbon source for the 87Sr/86Sr ratio of normal seawater DIC. cold seep carbonates for 0.70913~0.70918, indicating the carbonate diagenetic fluid is mainly affected by the impact of the bottom water, instead of deep fluid, which is on the other hand confirmed the formation of cold seep carbonates for micro bio methane Causes. By U-series part seep carbonate age determination of U-Th dating dating. Preliminary results show that the pit area of cold seep carbonates formed in 18.5-12.3 Ka, the last glacial maximum in different period, reflecting the methane venting Nyegga pit area is intermittent, experienced a number of active and dormant. Through the ancient fluid Delta 18O reconstruction oxygen isotope of carbonate rocks and biological value of the shell, the formation of cold seep carbonates in the last glacial maximum and ancient sea oxygen isotope in equilibrium, methane seep fluids probably derived from the deep release of methane hydrate decomposition little effect, heavy oxygen isotope decomposition on the release of oxygen isotope in seep carbonates in the shallow formation composition. Formed in the Holocene showed slightly biased (~+0.7%) of the 18O source, probably mainly by Shallow hydrate other factors that cause the tectonic activity of the decomposition. Based on the research results, that methane venting Nyegga pit area since 18 Ka are very active, much earlier than the last 8.1 landslide events Ka, therefore speculated that the methane seep in this area may lead to hydrate decomposition is one of the inducing factors in this area submarine landslide.

【學(xué)位授予單位】：中國科學(xué)院研究生院(廣州地球化學(xué)研究所)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：P736;P588.245

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