摘要
甲烷厌氧氧化作用（Anaerobic Oxidation of Methane,简称AOM）是海洋沉积物早期成岩过程中常见的地质作用,记录了沉积物埋藏压实期间海水下渗与沉积流体上涌过程中发生的硫酸盐还原和甲烷厌氧氧化等生物地球化学反应,形成了一套独特的自生矿物.通过实例分析东北太平洋IODP311航次U1328站位和南海北部陆坡GMGS2航次08站位的钻孔岩芯沉积物中自生矿物的类型和稳定碳、氧、硫同位素组成等,在U1328站位浅表层及约219m深度位置和在GMGS2-08站位15mbsf、60mbsf和84mbsf位置发现了AOM成因的自生碳酸盐类矿物,其δ13C值分别低至-41.50‰（VPDB）和-57.89‰（VPDB）,并且出现了富集的黄铁矿及其正偏硫稳定同位素组成,其δ34S值分别高达32.49‰（VCDT）和20.80‰（VCDT）.认为现代海洋沉积物中AOM成因的自生矿物能有效地记录海洋的甲烷异常渗漏事件,其矿物组合和稳定同位素组成可用于探索地史时期古海洋的甲烷渗漏事件.新元古代＂雪球地球＂结束后陡山沱组＂盖帽＂碳酸盐岩中极低碳稳定同位素的特征和扇状重晶石等自生矿物特征,指示了新元古代冰后期古海洋中曾经出现异常的甲烷渗漏事件,可能造成了古海洋环境和吉气候的突变.根据＂将今论古＂原理,利用AOM成因的自生矿物探索深时地球重大转折期古海洋的甲烷异常渗漏事件具有广阔的应用前景.
Anaerobic oxidation of methane （AOM） is one of common geological processes in early diagenesis of marine sediments and records the complex biogeological reactions of the sulfate reduction and AOM by the down-ward seawater and up-ward interstitial fluid in the progresses of sediment deposition and compaction, during which a couple of distinctly authigenic minerals are precipitated. Based on the studies of types of authigenic minerals and their stable isotopes of carbon, oxygen, sulfur within the cored sediments in site U1328 of IODP311 in northern Pacific Ocean and in site 08 of GMGS 2 （GMGS2-08） expedition in northeastern South China Sea, the AOM- derived authigenic carbonates were identified in shallow surface sediments and deep sediments about 219mbsf depth in site U1328 of IODP311. Meanwhile, three layers having AOM derived carbonates, high concentration of pyrites and positive excursions of δ34Spr were recognized in cored sediments from GMGS 2-08 site at depths about 15mbsf, 60mbsf and 84mbsf. The δ13C values of carbonates in sites U1328 and GSGM 2-08 show extremely negative values low to -41.50‰ （VPDB） and -57.89‰ （VPDB） respectively. The δ34S values of pyrites in sites U1328 and GMGS 2-08 show clear positive excursions with the values up to 32.49‰ （VCDT） and 20.80‰ （VCDT） respectively. Therefore, it is concluded that the authigenic minerals in modern marine environment could efficiently record the unusual AOM processes and could be used to recognize the unusual methane events, which therefore could be used to approach the ancient methane events in deep Earth. The brief introduction of extremely negative stable carbon isotopes and barite crystal fans in the Cap Carbonate of Neoproterozoic Doushantuo Formation could verify that there were unusual methane activities at the end of Neoproterozoic Snowball Earth, which might result into the dramatic changes of marine chemistry and climate at the end of Snowball Earth. In summary, based on the principle of ＂the present is the key to past＂ there are great prospective and significant insight to use AOM-derived authigenic minerals to decipher the ancient marine methane events in deep Earth especially during the key geological transit periods.
出处
《第四纪研究》
CAS
CSCD
北大核心
2015年第6期1383-1392,共10页
Quaternary Sciences
基金
国家自然科学基金项目（批准号：41472085和41172102）、国家重点基础研究发展规划项目（973项目）（批准号：2011CB808805）和中国地质调查局水合物勘查与试采项目（批准号：GZH20110030-50603,-6WX02）共同资助
作者简介
王家生 男 52岁 教授海洋地质学和地质学专业E-mail：js-wang@cug．edu．cn
