雅浦海沟北部深渊和超深渊沉积物的物质组成、来源和形成过程研究

Compositions, sources and formation processes of abyssal and hadal sediments in the northern Yap Trench

为探究雅浦海沟北部深渊、超深渊沉积物的组成、来源和形成特征,以1 cm分层对采自该海域不同深度的五根柱状沉积物样品的0~8 cm沉积层进行了扫描电子显微镜(SEM)观察和X射线能谱(EDS)分析,并且分析了这些样品的含水率,锰结核含量,Al、Ca、Fe、Mn、Ti、Mg等6种常量金属和Ba、Co、Cr、Ni、Pb、Sr、V、Cu、Zn等9种微量金属元素含量,以及总有机碳(TOC)含量等参数。结果表明,研究区域沉积物主要为深海软泥沉积,是不同年代沉积物的复杂混合,包含以盘星石为代表的颗石藻、海绵骨针、放射虫和硅藻等多种微体古生物化石以及辉石、重晶石、钛铁矿、长石等多种矿物。沉积组分主要来自生物源、火山源、陆源和海底热液,其中陆源沉积出现于海沟东侧深渊区。海沟西侧崖壁的沉积物比东侧崖壁的沉积物更容易发育锰结核。研究区域沉积物含水率较高并且颗粒较大,其含水率随深度增加呈减少趋势。研究区域超深渊站位沉积物的TOC和微体古生物化石含量均高于深渊站位,存在明显的漏斗效应。整体上海沟西侧崖壁沉积物含水率和TOC含量低于东侧崖壁的沉积物。自更新世以来,雅浦海沟北部的碳酸钙补偿深度(CCD)线从4 568 m以深变为4 435 m至4 568 m之间。研究区域的沉积环境为氧化环境,其0~8 cm沉积层的古老沉积物与现代沉积物发生了混合和再沉积作用,形成年代跨度极大。研究区域沉积物的形成受到海沟坡度、水动力环境、重力滑塌、浊流沉积、火山活动、漏斗效应等多种因素的显著影响。

To investigate the sediment compositions,sources,and formation processes in the abyss and hadal zone of the northern Yap Trench,scan electron microscope(SEM)and X-ray energy spectroscopy(EDS)were used to analyze in 1 cm interval of the 0-8 cm sediment layer of five core samples collected at different depths.The compositional analysis included water content,manganese nodule content,concentrations of six major metal elements(Al,Ca,Fe,Mn,Ti,Mg)and nine trace metal elements(Ba,Co,Cr,Ni,Pb,Sr,V,Cu,Zn),and total organic carbon(TOC).According to the analysis results,sediments in the study area are mainly deep-sea ooze,a complex mixture of sediments from different eras.They contain microfossils produced by coccolithophores,such as Discoaster,sponge spicules,radiolarians,and diatoms,and various minerals,including pyroxene,barite,ilmenite,and feldspar.The sediment sources are complex,including mainly biological,volcanic and terrestrial(found in the abyss on the west side of the trench)sources as well as submarine hydrothermal fluids.Manganese nodules develop more easily in sediments off the cliffs on the west side of the trench than on the east side.The abyssal and hadal sediments in the northern Yap Trench have relatively high water content and large particle size,and the water content tends to decrease with depth.The sediment TOC content and microfossil abundance are higher in hadal than in abyssal sediments,indicating obvious funnel effect.As a whole,the water and TOC content of the sediments are lower on the west side of the trench than on the east side.The carbonate compensation depth in the northern Yap Trench ranges between 4435-4568 m,changing from below 4568 m since the Pleistocene.The sedimentary environment in the study area is oxic,where mixing and redeposition of ancient and modern sediments occur in the 0-8 cm sediment layer,causing the formation age to vary greatly.Factors influencing sediment formation include trench slope,hydrodynamic environment,gravitational collapse,turbidity current deposition,volcanic activity,and funnel effect.