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

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。     

马里亚纳海沟南部海域沉积物的工程地质特性及其成因

大洋27航次中,在马里亚纳海沟挑战者深渊南翼斜坡上获得了箱式插管和重力柱状样品,并对这些样品现场进行了含水率、湿密度、微型扭力十字板、微型贯入和无侧限抗压强度试验,获得了深海表层沉积物的物理力学性质参数,具有较高的含水率、较低的密度、较大的孔隙比、较低的抗剪强度和贯入阻力,各项参数随深度增加呈现规律性变化。归航后通过对沉积物的粒度、碎屑矿物、黏土矿物、微体古生物的鉴定,进一步从物质组成、物质来源和沉积环境等方面对此特殊工程地质性质沉积物的成因进行分析。     

长江水系沉积物碎屑矿物组成及其示踪意义

长江碎屑矿物组成研究表明,轻矿物以石英、长石和岩屑为主,不同支流轻矿物组成特征不同,成熟度指数平均是2.0,一般干流高于支流,成熟度随沉积物搬运距离增加而增大。QFL及QtFL三角图解显示长江沉积物主要来自再旋回造山带物源区,流域风化剥蚀速度较快,不同支流物质汇入干流,使得干流轻矿物组成复杂多变而难以和支流区别。重矿物含量从长江上游至下游呈递减趋势,其主要组合是磁铁矿-普通角闪石-普通辉石-石榴子石-绿帘石-褐铁矿-钛铁矿。红柱石和磷灰石是金沙江沉积物的特征矿物组合;蓝晶石是岷江流域的特征矿物;涪江的特征矿物是榍石;汉江的特征矿物组合是磷灰石、紫苏辉石和硅镁石;锆石是湘江的特征矿物。不同流域的特征矿物指示其源岩性质。上游的雅砻江、大渡河以及岷江等支流沉积物对中、下游干流沉积物的贡献较弱。涪陵以上长江流域风化作用强烈,母岩主要是沉积岩类(碎屑岩、泥岩);其下流域沉积物中近源弱风化物质明显增加,其源岩类型体现为岩浆岩和变质岩类;而金沙江攀枝花地区及湘江、沅江沉积物则更多来自流域内广泛分布的大片变质岩类。     

REE示踪沉积物物源研究进展

ＲＥＥ作为一种重要的沉积物物源示踪剂运用很广。在介绍了ＲＥＥ性质的基础上，对海水、河水、沉积岩、河流及边缘海沉积物中的ＲＥＥ元素丰度与配分模式特征进行了深入综述，概述了影响和控制ＲＥＥ丰度、模式及分馏特征的主要因素；论述了ＲＥＥ的物泊示踪意义以及在国内外应用情况与存在问题：源岩风化对ＲＥＥ分馏的影响；颗粒运及沉积时水动力分选对ＲＥＥ分馏可能造成的影响，即不同粒级中的ＲＥＥ不同的丰度与配分模式和碎屑     

江汉平原主要河流沉积物磁学特征及其与物源区表壳岩性的响应

为了建立江汉平原沉积物示踪的磁学模型,对汇入江汉平原的主要河流现代沉积物磁学特征进行了研究,结果表明:(1)在江汉平原范围内,无论长江、汉江,还是周边的漳河、沮水、玛瑙河和清江,它们的现代沉积物的磁学参数特征均显示出明显的差异,而且和源区表壳岩性也显示出极好的相关性;(2)长江和汉江现代沉积物中铁磁性矿物均以亚铁磁性矿物为主,它们主导了样品的磁性特征,但长江沉积物比汉江沉积物亚铁磁性矿物含量高;(3)长江和汉江沉积物的亚铁磁性矿物晶粒都以假单畴-多畴为主,并且长江沉积物磁性颗粒总体上要比汉江的粗;(4)在汇入江汉平原的主要支流中,汉江的亚铁磁性矿物含量远远高于其他支流,且磁性矿物的晶粒也比其他支流的粗;(5)除汉江以外的支流中,玛瑙河沉积物中磁性矿物的晶粒比较细且不完全反铁磁性矿物含量较高,漳河中的超顺磁物质含量较高,而清江中不完全反铁磁性矿物含量较高且磁性矿物的晶粒相对较粗.上述结果表明,在江汉平原利用沉积物的磁学特征可达到沉积物物源示踪的目的.      

东太平洋洋底沉积物的物质组成与物理化学特征

作者通过研究,发现东太平洋洋底沉积物主要是由<0.063mm的伊利石、蒙脱石加混层矿物、高岭石、绿泥石粘土矿物和放射虫、硅藻等组成。具有碱性、比表面积大,离子交换容量大的特点。该成果无异为东太平洋多金属结核分布区的大洋地质学的研究,提供了可贵的环境地质资料。     

基于沉积物物质来源的地下水化学特征分析:以北京市平原区为例

沉积物物质来源不同,其沉积环境和沉积特征不同,其地球化学特征、水动力体系和地下水循环响应不同。文中以北京市平原区为例,通过沉积物物质来源分析,研究浅层地下水化学分布特征。首先根据地下水系统分区进行取样和实验,采用矿物组合、风化强度及相关分析等多种方法综合分析北京市平原区沉积物的物质来源及其组合特征,多种方法分析结论一致,即北京平原区的主要物质来源:一是流经燕山山地花岗岩变质岩区的潮白河系统,一是流经西山山地石灰岩区的永定河系统;而两系统中、下部是多期物源多层交叠、纵横交错沉积形成的。其次在物源分析基础上通过水质分析研究两系统剖面上地下水水化学特征,即两系统剖面地下水化学类型主要为HCO3--Ca.Mg型水;但永定河系统的溶解性总固体、阴阳离子浓度均大于潮白河系统,这与两剖面所在系统物源分析的结果相吻合,即分析结果表明物源的沉积环境及沉积组合特征决定了系统的地下水化学特征。     

长江河流沉积物磁铁矿化学组成及其物源示踪

运用电子探针分析了长江干流和主要支流河漫滩沉积物中磁铁矿的元素组成.磁铁矿中的FeO平均含量稍高于其标准组成,而Fe2O3平均含量则明显低于标准组成;Ti、Al、Cr、V、Mn、Mg、Co和Zn等元素在磁铁矿中含量变化大,不同支流的磁铁矿的元素组成不同,同一取样点不同样品磁铁矿的元素组成变化也较大.金沙江、湘江、汉江及长江干流磁铁矿与钛磁铁矿、钛尖晶石、钒钛磁铁矿和铬铁矿等出溶交生,TiO2、Cr2O3和V2O3等元素含量高且变化大.金沙江磁铁矿富Mg、Al和Cr;大渡河、雅砻江和岷江磁铁矿中微量元素含量大多低于0.5%;涪江、汉江磁铁矿富Ti和V,而湘江磁铁矿富Ti和Al;总体上,长江干流上游磁铁矿富Ti,而下游磁铁矿中Ti、Al、Cr、V、Mg和Mn含量低于0.15%.干流磁铁矿的元素组成变化反映主要支流源岩组成及对干流影响程度的差异.     

中太平洋CC区第四系沉积物地球化学特征及物源

根据对中太平洋CC区PC5356孔、PC5362孔及PC5417孔沉积物常量微量元素的测试结果，采用多元统计分析的方法，研究了该地区第四系沉积物中元素含量的空间分布和组合特征，探讨了其物质来源及沉积环境的垂向演变规律。中太平洋CC区第四系沉积物主要为钙质硅质黏土和钙质软泥，早期沉积物受火山活动的影响较大，晚期与生物作用密切相关。     

南黄海沉积物常量元素组成及物源分析

通过对南黄海295个站位沉积物样品的常量元素含量分析,研究了南黄海沉积物常量元素组成的R-型聚类分析、R-型因子分析及与物质来源的关系。南黄海沉积物常量元素Al2O3、MgO、K2O、Fe2O3分布基本相似;SiO2分布与Al2O3、MgO、K2O、Fe2O3分布相反;中、西部CaO、CaCO3分布与黄河、长江物源有明显关系;Na2O分布与黄河物质供给有关;TiO2分布反映了长江物质的运移方向。现代黄河物质及老黄河物质主要沉积于南黄海的西部、中部和东南部;海区东部物质反映来自朝鲜半岛物质的对南黄海东部的作用。长江物质主要局限于南黄海的西南和南部区域沉积;TiO2和Ti/Al分布反映了长江物质可能对南黄海中部区域也有所影响。     

川西坳陷中段中侏罗统沙溪庙组碎屑组分特征对物源的约束

为了深入探讨川西坳陷中段中侏罗统沙溪庙组的物源及其源区属性,应用碎屑岩碎屑组分特征及其Dickinson三角投点特征对研究区物源及其源区属性进行了深入讨论。结果表明,研究区东北部的中江、新都等地具有低石英、高长石特征,属于切割岛弧、基底隆起、过渡大陆的构造背景,而研究区西部的鸭子河、孝泉等地区具有高石英、低长石特征,且具有相对高的变质岩岩屑,属于再旋回造山带的构造背景。结合沙溪庙组沉积时期周缘造山带的演化特征,认为研究区东北部的中江、新都等地区物源主要来自北部的米仓山-大巴山,而西部的鸭子河、孝泉等地区物源主要来自西部的龙门山。     

海南岛北部晚新生代沉积物Sr-Nd同位素组成及其物源示踪

海南岛北部(琼北)巨厚的晚新生代沉积物记录了海南岛晚新生代气候与环境演化信息。但关于该沉积物Sr-Nd同位素方法的物源示踪研究还比较缺乏。以琼北钻遇基岩的钻孔(ZK1-5)为研究对象, 以Sr-Nd同位素组成为示踪手段, 开展了其物源示踪研究。结果表明: 海南岛北部于晚新生代中新世—更新世经历了从滨浅海相沉积—海陆交互相沉积—陆相沉积—火山喷发环境的转变, 中新世海相沉积Sr同位素比值(平均值0.727002)整体高于上新世海陆过渡相和更新世陆相沉积的Sr同位素比值(平均值0.714917), 表明海相沉积比海陆过渡相和陆相沉积风化程度更高。海相、海陆过渡相及陆相沉积的Nd同位素组成没有发生明显变化, 较一致, 表明海陆环境变迁并没有引起该地区物源发生重大变化。而琼北晚新生代沉积物εNd(0)值分布范围(-14.0~-5.1)与岛内花岗质岩石的εNd(0)值分布范围(-14.1~-5.2)基本一致, 与岛内变质岩(1.2~8.5)和玄武岩类岩石(1.9~7.8)的εNd(0)值差别较大, 表明其源岩主要来自海南岛花岗质岩石, 变质岩和玄武岩贡献较小, 这可能与岛内花岗质岩石分布范围广有关。对琼北地区晚新生代沉积物Sr-Nd同位素组成特征的认识, 有助于深入理解晚新生代海南岛风化过程及环境变化, 并对南海物源及古海陆环境重建具有重要意义。     

Rare-earth element geochemistry as a tracer for clarifying the provenance of the stream sediments in Namhan River, Korea

In the last forty years, the rare-earth elements （REEs） have been used as a powerful tool for solving various geological and geochemical problems due to their unique and chemically coherent behavior. The river sediments are produced by weathering, transportation and deposition. Nesbitt suggested that the rare-earth elements had been mobilized and fractionated during supracrustal alteration of the Torrongo granite, southeastern Australia. Nevertheless, recently, our replicate estimation for REE patterns in sediments revealed that there is nearly no variation in REE patterns. This suggests that invariability of REE patterns in weathering and solidification can be used as a tracer for constraining the provenance of stream sediments. In order to trace the pathway of the river sediments geochemically, based on the REE geochemistry from the river sediments and rocks, we have monitored the REE abundance of stream sediments at branch rivers of the Namhan River in South Korea for three years. The branches studied are Bokhacheon, Shinduncheon and Yanghwacheon. The sediments were divided into coarse （〉300 μm） and fine fractions （〈300 μm）. As a result, we could observe that major element compositions were similar to each other regardless of particle size and sampling date. This suggests that it is difficult to deduce a geochemical difference between river sediments based on major element composition and particle size. The geochemical characteristics of surrounding soils were similar to those of fine river sediments. And the chondrite-normalized REE patterns of most of the fine and coarse sediments in combination with grain sizes and drainage area showed very close relationship with the surrounding rocks. However, some sites showed that there were large variations in REE patterns including total REE abundance and Eu anomaly due to feldspars. This variation trend of REE patterns suggests that changes might have happened in sediment supply for the drainage system in the study area due to floods or large-scale construction.     

现代河流沉积物碎屑及矿物组分研究新进展

现代河流沉积物忠实地记录了流域盆地内的母岩、风化、搬运和沉积过程中的化学、物理过程以及人类活动的改造作用,是探索和验证源- 汇系统等理论的重要媒介。本文以全球现代河流砂组分数据库为基础,总结了碎屑组分、重矿物组分在不同大陆的分布特征,探讨了其在物源识别、源区贡献率计算、沉积物产生及搬运过程中气候- 构造等影响因素的评估、对源- 汇系统的研究启示等方面的应用。今后建议加强基于大数据的沉积物组分对气候- 构造- 人类活动的响应、沉积物产生及通量、高时间分辨率的沉积物组分变异性、不同物源定量化方法的差异等方面的研究。     

南海北部湾全新世以来沉积物地球化学特征及物源分析

为探讨全新世以来南海北部湾沉积物的沉积环境变化,对北部湾海域的SO-31沉积物柱状样进行了元素地球化学分析。根据元素地球化学的垂向分布特征,将SO-31沉积柱划分为3个单元,反映了全新世不同时期的区域海平面波动以及沉积物物源的变化。SO-31沉积柱的稀土元素配分曲线和La/Co与La/Sc散点图分析表明:111 400~12 800 a BP(全新世前期),研究区海平面较低,红河、其他周边河流及海岸侵蚀物均为本区的主要物源;28 500~1 1400 a BP(全新世早期),随着海平面的逐渐上升,河口和岸线逐渐后退,各物源供给区对本区沉积物的贡献量也发生了相应变化,相对而言红河贡献率有所下降;30~8 500 a BP(中全新世至今),区域海平面持续上升导致了琼州海峡打开,北部湾水动力环境和物源供给发生了剧变,红河对本区的物源贡献逐渐变小,而来自北部湾东部的物质成为本区沉积物的主要物源。     

Composition and origin of lipid biomarkers in the surface sediments from the southern Challenger Deep,Mariana Trench

The surface sediments collected from the southern Mariana Trench at water depths between ca. 4900 m and 7068 m were studied using lipid biomarker analyses to reveal the origin and distribution of organic matters. For all samples, an unresolved complex mixture (UCM) was present in the hydrocarbon fractions, wherein resistant component tricyclic terpanes were detected but C₂₇–C₂₉ regular steranes and hopanes indicative of a higher molecular weight range of petroleum were almost absent. This biomarker distribution patterns suggested that the UCM and tricyclic terpanes may be introduced by contamination of diesel fuels or shipping activities and oil seepage elsewhere. The well-developed faults and strike-slip faults in the Mariana subduction zone may serve as passages for the petroleum hydrocarbons. In addition, the relative high contents of even n-alkanes and low Carbon Preference Indices indicated that the n-alkanes were mainly derived from bacteria or algae. For GDGTs, the predominance of GDGT-0 and crenarchaeol, together with low GDGT-0/Crenarchaeol ratios (ranging from 0.86 to 1.64), suggests that the GDGTs in samples from the southern Mariana Trench were mainly derived from planktic Thaumarchaeota. However, the high GDGT-0/crenarchaeol ratio (10.5) in sample BC07 suggests that the GDGTs probably were introduced by methanogens in a more anoxic environment. Furthermore, the n-alkanes C₁₉–C₂₂ and the n-fatty acids C_20:0–C_22:0 were depleted in ¹³C by 3‰ compared to n-alkanes C₁₆–C₁₈ and the n-fatty acids C_14:0–C_18:0, respectively, which was interpreted to result from the preferential reaction of fatty acid fragments with carbon “lighter” terminal carboxyl groups during carbon chain elongation from the precursors to products. The abundance of total alkanes, carboxylic acids, alcohols and total lipids were generally increased along the down-going seaward plate, suggesting the lateral organic matter inputs play an important role in organic matter accumulation in hadal trenches. The extremely high contents of biomarkers in sample BC11 were most likely related to trench topography and current dynamics, since the lower steepness caused by graben texture and proximity to the trench axis may result in higher sedimentation rate. This paper, for the first time, showed the biomarker patterns in surface sediments of the Mariana Trench and shed light on biogeochemistry of the hardly reached trench environment.     

Geochemical and Nd isotope composition of detrital sediments on the north margin of the South China Sea: provenance and tectonic implications

A major re‐organization of regional drainages in eastern Tibet and south‐western China took place in the Cenozoic as deformation from the growing Himalayas and Tibetan Plateau affected an increasingly wider area. The effects of these changes on the regional sediment routing systems is not well constrained. This study examines the geochemical and Nd signatures of sedimentary rocks from the Ying‐Qiong and Nanxiong basins on the northern margin of the South China Sea to constrain and identify any significant changes in sediment source. Upper Cretaceous to Lower Eocene sedimentary rocks in the Nanxiong Basin show higher Th/Sc, La/Sc, Th/Cr and Th/Co ratios and lower Eu/Eu* ratios than PAAS (post‐Archaean Australian Shale), which indicates that Palaeozoic sedimentary rocks of the South China Block were the main basin sediment source. In contrast, Oligocene to Pleistocene sedimentary rocks of the Ying‐Qiong Basin show an abrupt change in these trace‐element ratios between 16·3 and 10·4 Ma, indicating a mid‐Miocene shift in provenance. ɛ_Nd values from the Ying‐Qiong Basin (range = −11·1 to −2·1) reinforce this, with pre‐13·8 Ma sedimentary rocks having average ɛ_Nd of −5·6 (range = −2·1 to −7·4), and post‐13·8 Ma sedimentary rocks having average ɛ_Nd of −9·3 (range = −8·7 to −11·1). During the Oligocene, the centre of rifting transferred south and basins on the north margin of the South China Sea experienced rapid subsidence. Further uplift and erosion then exposed Mesozoic and Cenozoic granites that supplied large amounts of granitic detritus, especially to the Ying‐Qiong Basin. Then a change occurred at ca 13 Ma resulting in less input from local sources (i.e. the fault blocks formed by Mesozoic‐Cenozoic tectonics and magmatism) to an increasing contribution of older continental material, mostly from Indochina to the west of the South China Sea.