马里亚纳海沟沉积物物源示踪和沉积环境分析  

Preliminary study on source and sedimentary environment in the Mariana Trench

作　　者：宋子君 孟凡祎 李维鼎 陈琳莹 罗敏[1] SONG Zijun;MENG Fanyi;LI Weiding;CHEN Linying;LUO Min(Shanghai Engineering Research Center of Hadal Science and Technology,College of Marine Sciences,Shanghai Ocean University,Shanghai 201306,China)

机构地区：[1]上海海洋大学海洋科学学院,上海深渊科学工程技术研究中心,上海201306

出　　处：《海洋地质与第四纪地质》2022年第4期84-95,I0001-I0005,共17页Marine Geology & Quaternary Geology

基　　金：国家自然科学基金面上项目“新西兰Hikurangi俯冲带孔隙流体来源和水岩作用示踪研究:对流体活动和慢滑移事件的指示”(42076057),“马里亚纳海沟和新不列颠海沟深渊海底沉积物孔隙水溶解有机质特征及来源”(42176069);上海市2021年度“科技创新行动计划”启明星项目“深渊海底沉积物溶解有机质荧光光谱特征研究”(21QA1403700)。

摘　　要：深渊海沟(水深>6 000 m)作为地球表层的最深处,具有特殊的地形地貌和沉积过程,被认为是沉积物最终的汇。通过对采集于马里亚纳海沟南端水深为5 800~10 954 m的4个站位沉积物开展沉积地球化学研究,旨在揭示不同水深沉积物组成的差异,判别沉积物的来源和沉积环境的变化。主、微量元素含量、Sr-Nd同位素和黏土矿物组成的分析结果显示,马里亚纳海沟不同水深沉积物组成差别较大,整个MBR05和MBR06岩芯8~20 cm范围均发现大量有Ethmodiscus rex (E. rex)组成的硅藻席沉积(laminated diatom mats, LDMs)。沉积物碎屑组分基本上是陆源风尘端元和火山物质端元的混合,且含有硅藻席沉积物的陆源风尘贡献比例更大,表明大盘筛藻大型成席硅藻的勃发可能与亚洲风尘输入有关。同时,稀土配分模式和Ce异常显示硅藻席形成于次氧化沉积环境,而不含硅藻席沉积物形成于氧化的沉积环境,可能是由于末次盛冰期风尘输入增强,刺激硅藻席勃发后快速堆积至海底,导致有机质矿化增强,进而引起沉积环境的变化。本研究对于认识深渊不同水深沉积物组成的异质性及其对底栖微生物的分布、生态和活动强度的影响有指示意义。Hadal trenches(>6 000 m) represent the deepest parts on the Earth’s surface in unique topography and sedimentary processes, and are considered the final sink of sediments. The strontium(Sr) and neodymium(Nd) isotope compositions and clay-mineral assemblages of the detrital fraction of sediments in the southern Mariana Trench, as well as the concentrations of major and trace elements of bulk sediments at water depths of 5 800~ 10 954 m were analyzed to trace the sediment provenance and distinguish the changes in the sedimentary redox conditions. The whole Core MBR05 and the interval of 8~20 cm of Core MBR06 are dominated by valve fragments of the giant diatom Ethmodiscus rex, forming laminated diatom mats(LDMs). Both Sr-Nd isotope compositions and clay-mineral assemblages of the detrital fraction reflect a two-component mixing pattern consisting of Luzon Arc volcanic clastics and Asian aeolian dusts, showing greater aeolian dust contribution on the LDMs, indicating that the bloom of E. rex may be related to Asian aeolian dust input. Meanwhile, the rare earth elements(REEs) distribution pattern and weak or absent Ce anomalies in the LDM point to suboxic conditions during the LGM formation, while the nonLDM samples exhibit vey low to zero enrichment of redox-sensitive elements and negative Ce anomalies, indicating the deposition under oxic bottom-water conditions. It is inferred that changes in sedimentary environments is associated with the enhanced mineralization of organic matter caused by the rapid deposition of E. rex giant diatom. The bloom of E. rex giant diatom may be caused by the enhanced input of wind dust during the Last Glacial Maximum. This study is of relevance for understanding the heterogeneity of sediment composition in different water depths of hadal trench and its impact on the distribution, ecology, and activity intensity of benthic microorganisms in the trench areas.

关 键 词：锶钕同位素 黏土矿物 硅藻席 物源 沉积环境 马里亚纳海沟 

分 类 号：P736.4[天文地球—海洋地质]