台西南深海底栖有孔虫及其5万年来冷泉微生境变迁记录  

Deep sea benthic foraminifera from the Taixinan Basin and changes of their cold seep microhabitats during the past 50000 years

作　　者：苏新[1] 曲莹[1,2] 陈芳 杨胜雄[3,4] 周洋 崔鸿鹏[1] 于翀涵 滕田田[1] SU Xin;QU Ying;CHEN Fang;YANG Shengxiong;ZHOU Yang;CUI Hongpeng;YU Chonghan;TENG Tiantian(School of Ocean Sciences,China University of Geosciences(Beijing),Beijing 100083,China;Academy of Mathematics and Systems Sciences,Chinese Academy of Sciences,Beijing 100083,China;Guangzhou Marine Geological Survey,Guangzhou 510075,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 511458,China)

机构地区：[1]中国地质大学(北京)海洋学院,北京100083 [2]中国科学院数学与系统科学研究院,北京100083 [3]广州海洋地质调查局,广东广州510075 [4]南方海洋科学与工程广东省实验室(广州),广东广州511458

出　　处：《地学前缘》2020年第6期255-275,共21页Earth Science Frontiers

基　　金：国家自然科学基金项目(40672005,41776066);国家重点基础研究发展计划“973”项目(2009CB219502)。

摘　　要：为探讨冷泉区底栖有孔虫组合特征、受控因素及其冷泉微生境随时间的变迁,本文对台西南海盆取自九龙甲烷礁和海洋四号区冷泉区的973-4和973-5两根岩心展开了底栖有孔虫及其壳体氧碳同位素研究。测年结果揭示两根岩心为晚更新世约5万年来海洋氧同位素期(MIS)MIS 3至MIS 1早期的沉积序列。两个站位共识别了底栖有孔虫79属233种,优势类别在973-4组合中为Uvigerina(23.3%)、Bulimina(10.71%)和Cibicidoides(9.87%),在973-5组合中是Bulimina(20.6%),两站位的组合优势和常见属种均以内生类别为主。有孔虫分异度显然同时受到正常深海环境因子TOC和沉积物粒度的影响。总体上,优势和常见类群与TOC相关性较弱,但与δ18 OUvigerinaspp.有不同程度的相关性,说明有孔虫还受冷泉特殊营养物质和流体因子影响。5万年来,973-4和973-5站位底栖有孔虫组合生活的冷泉微生境,经历了由双壳-自生碳酸盐岩(MIS 3至MIS 2早期)向双壳-菌席(MIS 2晚期至MIS 1早期)的变迁。底栖有孔虫的优势类群也随微生境的变迁而演替,如973-4站位MIS 3-MIS 1的优势类群依次为U.peregrina、Cibicidoide-Bulimina、U.vadescens和Cibicides,973-5站位为Chilostomella+Globobulimina、Cibicidoides、Bulimina。有孔虫壳体氧碳同位素特征也随时间改变,从MIS 3到MIS 2早期,在自生碳酸盐岩水岩交换背景下,具有富δ18 O和亏损δ13 C特点(3.5‰~4.49‰,-2‰^-0.2‰);MIS 2晚期-MIS 1早期因双壳和菌席的生物地球化学作用影响,具有略富集δ18 O和略微亏损δ13 C的特征(2.5‰~3.5‰,-1‰^-0.1‰)。自5万年来两个区甲烷渗漏逐渐减弱,其间发生了几次增强事件。973-4站位记录了1次持续时间约10ka的增强事件(35~25ka);973-5站位记录3次(45ka,35ka,14~12ka)。其中,45ka时海底上涌的甲烷通量可能最大,在海底表面形成水合物。35ka时的甲烷喷溢增强事件可能为区域性事件。Benthic foraminifera and their shell oxygen and carbon isotopes from Core 973-4,located on the slope of the Jiulong Methane Reefs cold seep area,and Core 973-5 on the edge of the Haiyang No.4 Site in the Taixinan Basin,were studied to understand the characteristics of fauna assemblages,their ecological factors,and the change in microhabitats with time.The ages of sediments from the two cores were determined to be 50 ka,which were assigned to the late Pleistocene Marine Oxygen Isotope Stage MIS 3 to early MIS 1.In total,233 species of 79 genera were identified for the benthic faunas from the two cores.The dominant taxa from Core 973-4 were Uvigerina(23.3%),Bulimina(10.71%)and Cibicidoides(9.87%),while from Core 973-5 was Bulimina(20.6%).Generally,these two faunas were dominated by infauna taxa.Foraminiferal diversity was influenced by TOC and sediment grain sizes.A weak correlation between dominant(or common)taxa with TOC and varying degree of correlation withδ^18O Uvigerina spp.indicated that foraminifera taxa were also affected by other special nutrition and fluids in the cold seep areas.Over the last 50 ka,the microhabitats of benthic foraminiferal assemblages from Cores 973-4 and 973-5 changed from bivalve shell debris-authigenic carbonates(MIS 3 to early MIS 2)to bivalve-bacterial mats(late MIS 2 to early MIS 1).Correspondingly,from MIS 3 to MIS 1,the dominant taxa of foraminiferal assemblages from Core 973-4 changed from U.peregrina to Cibicidoides Bulimina then to U.vadescens Cibicides and from Core 973-5 changed from Chilostomella+Globobulimina to Cibicidoides then to Bulimina.Oxygen and carbon isotopic profiles of foraminiferal shells also changed with time,showing enrichedδ^18O(3.5‰-4.49‰)and depletedδ^13C(-2.0‰to-0.2‰),as results of exchanging ambient pore fluids with authigenic carbonates during the period of MIS 3 to early MIS 2 and biogeochemical processes in the microhabitats of bivalve and bacterial mats during the time of late MIS 2 to early MIS 1.Generally,the activity of methane seepi

关 键 词：底栖有孔虫 氧碳同位素 冷泉微生境 MIS 3-MIS 1期 台西南盆地 

分 类 号：P52[天文地球—古生物学与地层学]