CARBON STABLE ISOTOPIC COMPOSITION OF BENTHIC FORAMINIFERS FROM THE NORTH OF THE SOUTH CHINA SEA: INDICATOR OF METHANE-RICH ENVIRONMENT
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摘要: 对南海北部陆坡东沙海域、神狐海域及西沙海槽甲烷渗漏环境和无甲烷渗漏环境87个浅表层沉积物中的底栖有孔虫Uvigerina spp.进行碳同位素分析研究,结果表明,东沙海域δ13C值为-0.52‰~-5.68‰,平均值为-1.41‰,出现明显的负偏移;神狐海域δ13C值介于-0.36‰~-1.10‰,平均值为-0.75‰,未见明显的δ13C值负偏移;西沙海槽δ13C值介于-0.01%~-0.89‰,平均值为-0.45‰;对Uvigerina spp.碳同位素组成与沉积物有机碳(TOC)、甲烷(CH4)间的关系进行探讨,发现δ13C负偏移主要出现在甲烷渗漏环境,发生在末次盛冰期,与溶解无机碳负偏移以及沉积物全样的δ13C值负偏移层位相吻合,有可能作为富甲烷环境的替代指标。Abstract: Carbon stable isotopic composition of benthic foraminifers in piston cores and surface sediments from the north of the South China Sea have been studied. The carbon stable isotope analyses of infaunal species (Uvigerina spp.) revealed a distinction between seep and non-seep foraminifera.Uvigerina spp.collected from Dongsha area (seep environment) exhibited highly variable and strongly depleted δ13C values,ranging from -0.52‰ to -5.68‰ and the mean values -1.41‰; The Uvigerina spp. δ13C values ranged from -0.36‰ to -1.10‰, mean -0.75‰ in Shenhu area(non-seep environment); and δ13C values ranged from -0.01 to -0.89‰, mean -0.45‰ in Xisha Trough (non-seep environment). The relations between δ13C values,organic carbon (TOC) and methane (CH4) content showed that carbon isotopic ratios had a negative excursion trend with methane conent increasing. Negative carbon isotopic excursion of Uvigerina spp. mostly occurred during LGM, when dissolved inorganic carbon of bottom water and δ13C of core sediments were negative excursions. The studies imply that the carbon isotopic excursion may be used to indicate methane-rich environment.
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