中国东部入海河流沉积物磁性矿物化学特征及物源意义

大量陆源碎屑物质主要通过以长江、黄河为代表的大江大河和以瓯江、浊水溪为代表的山溪性小河流的携带输移至中国东部海域,海域沉积物的物源识别是当前的研究热点。本文通过原子吸收光谱法测试了磁性矿物中的11种元素（Ti、Fe、Cr、Mg、Al、V、Ca、Co、Zn、Mn和S）,旨在探讨这些河流沉积物（ < 45μm）的磁性矿物群体化学特征,提取其物源指示意义,为边缘海沉积物物源判别提供依据。研究结果表明,这些河流沉积物的磁性矿物主要是以铁氧化物（磁铁矿）为主,铁硫化物含量很低（ < 2%）,只有台湾浊水溪沉积物中含有相对较多的铁硫化物（主要是磁黄铁矿）,为1.84%。除此之外,各河流沉积物磁性矿物中铁氧化物的化学元素组成（Ti、Mg、Ca、Al、Cr、V、Mn、Co和Zn）差异也很明显,其中黄河富含Mg和Ca,长江富含Ti,钱塘江富含Al,瓯江富含Cr,台湾浊水溪相对来说富含Al和Co,而其余元素含量远低于其他河流。从磁性矿物成因图上看,黄河沉积物中磁性矿物落在碱性岩浆岩成因区,但这并不是反映了流域磁性矿物的母岩为碱性岩浆岩,而是由于流域中黄土土壤化过程中产生的细颗粒磁性矿物中含有较高的碱土金属元素（如Mg和Ca）所致;其他河流磁性矿物成因与其流域母岩关系密切,如长江和浙闽河流主要为超基性-基性-中性岩浆岩成因,浊水溪为沉积变质-接触交代成因,都与其所处流域的磁性矿物的母岩类型较为一致。利用Ti+V-S+Co-Ca+Mg三角图可以有效地区分黄河、长江和浙闽河流、浊水溪沉积物物源。磁性矿物群体中的Mn、Zn、Al、Cr元素的差异有助于进一步确定长江和浙闽河流的泥沙来源。同时,发现磁性矿物单颗粒和群体化学组成特征具有一定差异性,很可能是由于分析方法不同所造成。

     

Sediment provenance of late Quaternary morainic,fluvial and loess‐like deposits in the southwestern Verkhoyansk Mountains (eastern Siberia) and implications for regional palaeoenvironmental reconstructions

A provenance analysis of late Quaternary deposits from tributaries of the Aldan and Lena rivers in Central Yakutia (eastern Siberia) was carried out using analysis of heavy minerals and clay mineralogy. Cluster analysis revealed one assemblage that is characterized by relatively high proportions of amphibole, orthopyroxene and garnet as well as pedogenic clay minerals, reflecting a sediment provenance from the wide catchment area of the Lena and Aldan rivers. In contrast, the three other clusters are dominated by stable heavy minerals with varying amounts of clinopyroxene, apatite and garnet, as well as high percentages of illite and chlorite that are indicative of source rocks of the Verkhoyansk Mountains. Glacial moraines reveal the local mountain source signal that is overprinted by the Lena‐Aldan signal in the oldest moraines by reworking processes. Alluvial sediments in the Verkhoyansk Foreland show a clear Lena source signal through intervals of the middle and late Pleistocene, related to a stream course closer to the mountains at that time. Loess‐like cover sediments are characterized by the dominant Lena provenance with increasing proportions of local mountain sources towards the mountain valleys. Aeolian sands in an alluvial terrace section at the mountain margin covering the time between 30 ka and 10 ka BP reflect temporarily dominant inputs of aeolian materials from the Lena Plains. Copyright © 2007 John Wiley & Sons, Ltd.     

青藏高原东缘宜宾地区第四纪河流沉积物中铁质重矿物特征及物源意义

大河流域的发育史和演化在地学界广受关注。探讨宜宾地区第四纪沉积物中铁质重矿物的特征,可为长江流域的演化提供重要证据,同时对于了解青藏高原东缘的隆升及沉积响应具有重要意义。本文以金沙江和岷江交汇处的宜宾地区第四纪沉积物中的铁质重矿物为研究对象,分析其在电子探针和背散射图像中的化学和形貌学特征,探究长江及其支流的物源演化过程。研究结果显示:岷江下游Ⅴ级阶地至Ⅳ级阶地沉积以磁铁矿为主,物源主要来自龙门山构造带;Ⅲ级阶地沉积以钛铁矿为主,物源仍然主要来自龙门山构造带;现代沉积中蓝晶石、磷灰石等包裹体的铁质矿物增多,其物源来自龙门山构造带和松潘—甘孜褶皱带。岷江Ⅴ级至Ⅲ级阶地形成时,岷江的源头主要位于龙门山构造带;Ⅲ级阶地形成以后,岷江不断向上溯源侵蚀,深入松潘—甘孜褶皱带内,逐渐形成现代岷江。金沙江Ⅴ级阶地和长江Ⅴ级阶地中均未出现攀枝花钒钛磁铁矿,此时金沙江攀枝花—宜宾河段未贯通,长江此时在研究区的物源主要由发源于龙门山构造带的岷江提供。金沙江Ⅳ级阶地中攀枝花钒钛磁铁矿大量出现,表明此时金沙江攀枝花—宜宾河段已经贯通,时间为Ⅳ级阶地开始沉积的时间,即0.5~0.3 Ma BP。     

库姆塔格沙漠东南缘BL砂黄土剖面的沉积过程与物源分析

通过对库姆塔格沙漠东南缘BL砂黄土剖面观测、描述和采样,分析了沉积物粒度、年代、沉积环境和地球化学元素特征,结果表明：1）BL剖面沉积物颗粒的93.34%为砂和粉砂,证明剖面为一砂黄土沉积地层;2）BL砂黄土剖面地层沉积的开始年代为全新世早期（8.3ka）,是阿尔金山东部冰川消融后在特定的地形环境条件下形成的。地表沉积环境在全新世开始到8.3ka之间,受到了阿尔金山冰川和冰缘带融水的泛滥冲刷,难以形成沉积,8.3ka之后冰川积雪融水减少后在高凸的合适地形开始了连续沉积,由此形成了BL砂黄土沉积地层。BL地层沉积速率约为4.22cm/100a,早期沉积速率较快,后期则有所减缓;3）对比BL剖面沉积物特征元素比值分布模式,其与库姆塔格沙漠表层砂、内部出露地层（全新世以来）的不同沉积物特征元素比值分布模式具有极其相似的特征,证明两者的物质具有同源性,BL剖面的沉积物来源就是库姆塔格沙漠表层或者内部地层翻出来的物质。BL砂黄土沉积的过程和物源的研究为今后研究全新世以来库姆塔格沙漠区域古气候过程奠定科学的基础。

     

The hydrodynamic and sedimentary setting of nearshore coral reefs, central Great Barrier Reef shelf, Australia: Paluma Shoals, a case study

The Great Barrier Reef (GBR) shelf contains a range of coral reefs on the highly turbid shallow inner shelf, where interaction occurs with terrigenous sediments. The modern hydrodynamic and sedimentation regimes at Paluma Shoals, a shore‐attached ‘turbid‐zone’ coral reef, and at Phillips Reef, a fringing reef located 20 km offshore, have been studied to document the mechanisms controlling turbidity. At each reef, waves, currents and near‐bed turbidity were measured for a period of ≈1 month. Bed sediments were sampled at 135 sites. On the inner shelf, muddy sands are widespread, with admixed terrigenous and carbonate gravel components close to the reefs and islands, except on their relatively sheltered SW side, where sandy silty clays occur. At Paluma Shoals, the coral assemblage is characteristic of inner‐shelf or sheltered habitats on the GBR shelf (dominated by Galaxea fascicularis, up to >50% coral cover) and is broadly similar to that at Phillips Reef, further offshore and in deeper water. The sediments of the Paluma Shoals reef flats consist of mixed terrigenous and calcareous gravels and sands, with intermixed silts and clays, whereas the reef slope is dominated by gravelly quartz sands. The main turbidity‐generating process is wave‐driven resuspension, and turbidity ranges up to 175 nephelometric turbidity units (NTU). In contrast, at Phillips Reef, turbidity is <15 NTU and varies little. At Paluma Shoals, turbidity of >40 NTU probably occurs for a total of >40 days each year, and relatively little time is spent at intermediate turbidities (15–50 NTU). The extended time spent at either low or high turbidities is consistent with the biological response of some species of corals to adopt two alternative mechanisms of functioning (autotrophy and heterotrophy) in response to different levels of turbidity. Sedimentation rates over periods of hours may reach the equivalent of 10 000 times the mean global background terrigenous flux (BTF) of sediment to the sea floor, i.e. 10 000 BTF, over three orders of magnitude greater than the Holocene average for Halifax Bay of <3 BTF. As elsewhere along the nearshore zone of the central GBR, dry‐season hydrodynamic conditions form a primary control upon turbidity and the distribution of bed sediments. The location of modern nearshore coral reefs is controlled by the presence of suitable substrates, which in Halifax Bay are Pleistocene and early Holocene coarse‐grained (and relatively stable) alluvial deposits.     

南黄海沉积物磁性特征及其对物源变化的指示 ——以南黄海中部泥质区YSC-10孔为例

南黄海中部泥质区是东亚大陆沉积物巨大的汇,识别这一地区的物源变化对理解古气候和古海洋变化有重要作用.基于黄河和长江携带的碎屑物质在磁性特征上的差异,环境磁学参数、磁化率—中值粒径的相关性可用于指示南黄海中部泥质区物源的可能变化.根据YSC?10孔环境磁学参数变化和磁化率—中值粒径的相关关系,推测4.8 cal ka B...     

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。     

Evolution of the Palaeotethys in the Eastern Mediterranean: a multi-method approach to unravel the age,provenance and tectonic setting of the Upper Palaeozoic Konya Complex and its Mesozoic cover sequence (south-central Turkey)

ABSTRACT

Siliciclastic sediments from the Upper Palaeozoic Konya Complex and its Mesozoic cover were studied by a multi-method approach combining thin-section petrography, bulk-rock geochemistry, mineral chemistry of rutile, and U–Pb geochronology of detrital zircons. Provenance sensitive data of samples from the Upper Palaeozoic Hal?c? Formation indicate sediment supply from mainly low- to medium-grade metamorphosed sedimentary rocks of felsic character, while the contribution from volcanic rocks was rare. The detrital zircon record of sediments from the Hal?c? Formation documents sediment supply from different sources and excludes a similar provenance. Some samples show great similarities with Palaeozoic sandstones from the cover sequence of the Saharan Metacraton and the Arabian–Nubian Shield, while the other samples indicate a provenance that must be sought in units with a southern Eurasian affinity. The upper limit for sediment deposition in the Hal?c? Formation is mostly constrained by Early Palaeozoic zircon populations; however, sediment accumulation in Pennsylvanian–Cisuralian time is more likely, contemporaneously with the Upper Palaeozoic succession on the Karaburun Peninsula (western Turkey). The provenance of sediments from the Upper Triassic Ard?çl? Formation remains enigmatic, but the source should be sought nonetheless in units close to the depositional site. In any case, detrital zircon age spectra and compositional data exclude recycling of underlying rock units (i.e. Hal?c? Formation). Overall, our new provenance data reveal great similarities between the Konya Complex and comparable units (Chios, Karaburun) but also highlight distinct differences in terms of sediment composition and provenance.     

潮滩表层沉积物磁性特征的季节性变化及其对沉积动力作用的响应:以杭州湾北岸为例

根据2004年9月—2005年8月杭州湾北岸中潮滩固定观测点重复采集的表层沉积物的磁学参数和粒度分析,探讨了研究区域潮滩沉积物磁学性质的季节性变化及其对沉积动力的响应。 结果表明, 该观测点潮滩沉积物磁学参数存在显著的月际变化,2004年12月底—2005年5月上旬的半年中,SIRM、χARM、χfd%、χARM/χ、χARM/SIRM等参数出现高值,指示了沉积物中含有较多的细晶粒亚铁磁性矿物,对应于潮滩淤积时段和较细的沉积物粒级组成,其余各月上述磁参数值较低,对应于潮滩沉积物较粗的侵蚀期。上述结果表明,沉积物的磁性特征可以很好地反映潮滩冲淤过程中沉积动力的变化。     

熔片制样-X射线荧光光谱法测定海洋沉积物样品中主次量组分

采用混合熔剂熔融制备样片,用Axios X射线荧光光谱仪测定海洋沉积物样品中SiO2、Al2O3、Fe2O3、MgO、CaO、Na2O、K2O、P2O5、TiO2、MnO、BaO、Ni、Cu、V、Cr和Zn等16种组分,用理论α系数校正基体效应,分析方法的精密度(RSD,n=12)为Cu和Cr小于6%,其余大多数主次量组分小于2%.方法用海洋沉积物国家一级标准物质验证,测定值与标准值相符.     

原子荧光光谱法测定土壤和水系沉积物国家标准物质中砷

用王水浸提法和硝酸-高氯酸-氢氟酸混合酸消解法处理样品,原子荧光光度光谱法测定土壤和水系沉积物国家标准物质样品中的砷。方法检出限为0.02 mg/kg。两种前处理方法砷的测定值与标准值相符,均可以满足土壤和水系沉积物样品中砷含量的测定要求。单纯测定样品中砷含量时,王水浸提法更好;如果在测定砷同时还要测定其他元素,则可以选用混合酸消解法。     

自制氢化物发生系统与电感耦合等离子体发射光谱法联用测定土壤和水系沉积物中的砷锑铋

氢化物发生法-电感耦合等离子体发射光谱(ICP-OES)联用可以提高仪器测定的灵敏度,但氢化物发生的化学反应过程不稳定,导致检测精密度变差。本文设计了一套简易氢化物发生系统,将样品进样管内径由0.32 mm扩大为0.76 mm,与还原剂(硼氢化钾)管路通过三通混合,混合后反应管内径由0.76 mm扩大为1.14 mm,反应管长度由30 cm延长至50 cm,显著增加了待测元素氢化反应的空间和时间,使氢化反应达到平衡态从而提高了氢化物的稳定性。土壤和水系沉积物样品用盐酸-硝酸水浴浸提、硫脲-抗坏血酸预还原后利用此套系统与ICP-OES联用测定了砷锑铋的含量。砷锑铋的检出限分别为0.35μg/g、0.33μg/g、0.25μg/g,测定范围分别为1.1~300μg/g、1.0~100μg/g、0.75~100μg/g,均满足了相关分析要求。     

等离子体发射光谱法测定土壤和沉积物中6个常量元素结果不确定度评定

采用等离子体发射光谱法对测定土壤和水系沉积物中铝、铁、钙、镁、钾、钠6个常量元素进行系统的不确定度评定。不确定度的来源主要包括分析过程中所用的天平、玻璃器皿、标准曲线、标准溶液、试液定容体积及测量重复性等引入的不确定度分量。计算出各分量的不确定度,通过合成得到测量结果的合成不确定度、扩展不确定度及测试结果的报告形式。     

磁性层顶底埋深的功率谱计算方法及影响因素

功率谱法是计算磁性层顶、底界面埋深的常用方法之一,但是它在实际应用过程中受到一些因素的影响,可能会使解释结果产生偏差.利用磁异常功率谱对二度磁性体的顶、底界面埋深进行计算,通过对其高阶导数的功率谱计算埋深的近似公式的分析,探讨了影响功率谱计算埋深的因素,提高了该方法的可靠性.     

多向观测电感耦合等离子体发射光谱法同时测定土壤和水系沉积物中常量和微量元素

采用电感耦合等离子体发射光谱法同时测定土壤和水系沉积物样品中Al、Fe、Ca、Mg、K、Na、P、Ba、Be、Cd、Ce、Co、Cr、Cu、Li、Mn、Mo、Ni、Pb、Ti、V、W、Zn等23个常量和微量元素。各元素选择光谱干扰少、准确度高的多向观测方式(轴向、径向、轴向衰减、径向衰减),结合多元光谱拟合技术校正光谱干扰,改善方法的检出限及精密度。结果表明,方法的回收率为94.0%~103.4%,精密度(RSD,n=10)低于3.0%。方法经国家一级标准物质验证,测定值与标准值基本相符。     

偏硼酸锂熔矿-超声提取-电感耦合等离子体发射光谱法测定岩石水系沉积物土壤样品中硅铝铁等10种元素

采用偏硼酸锂熔矿分解样品,超声波振动提取,电感耦合等离子体发射光谱法同时测定同一份溶液中的硅、铝、铁、钙、镁、钾、钠、磷、锰、钛等组分。通过对岩石、水系沉积物和土壤国家一级标准物质测定验证,方法的准确度、精密度能够满足样品中各元素定量分析的要求。     

Sediment storage and severity of contamination in a shallow reservoir affected by historical lead and zinc mining

A combination of sediment-thickness measurement and bottom-sediment coring was used to investigate sediment storage and severity of contamination in Empire Lake (Kansas), a shallow reservoir affected by historical Pb and Zn mining. Cd, Pb, and Zn concentrations in the contaminated bottom sediment typically exceeded baseline concentrations by at least an order of magnitude. Moreover, the concentrations of Cd, Pb, and Zn typically far exceeded probable-effects guidelines, which represent the concentrations above which toxic biological effects usually or frequently occur. Despite a pre-1954 decrease in sediment concentrations likely related to the end of major mining activity upstream by about 1920, concentrations have remained relatively stable and persistently greater than the probable-effects guidelines for at least the last 50 years. Cesium-137 evidence from sediment cores indicated that most of the bottom sediment in the reservoir was deposited prior to 1954. Thus, the ability of the reservoir to store the contaminated sediment has declined over time. Because of the limited storage capacity, Empire Lake likely is a net source of contaminated sediment during high-inflow periods. The contaminated sediment that passes through, or originates from, Empire Lake will be deposited in downstream environments likely as far as Grand Lake O’ the Cherokees (Oklahoma).     

井中三分量磁测确定矿体方位和空间位置的方法

井中三分量磁测能较好地判断异常体的性质,进而判断磁性体的方位和空间位置,通常联合地面磁测可以更准确地判断地下矿体赋存情况,确定矿体产状、延伸方向及延深,指导布钻,提高见矿率.笔者主要分析了球体、薄板状体的磁场分布特征,总结磁场分布特征与磁性体的方位、磁化方向、倾斜方向等之间的相互对应关系,研究判断矿体方位、确定矿体空间位置的方法.井中三分量磁测是配合钻探寻找地下深部磁性矿体、了解其赋存情况的有效手段.将该方法应用于海南石碌铁矿某工区ZK1102井,提高了确定地下矿体空间位置的精确度,为继续钻进、终止布孔工作以及磁性矿体的储量评估提供参考.     

Generation and emplacement of Triassic granitoids within the Songpan Ganze accretionary-orogenic wedge in a context of slab retreat accommodated by tear faulting,Eastern Tibetan plateau,China

The eastern Songpan Ganze accretionary-orogenic wedge (northern Tibetan plateau) is characterized by extensive magmatism coeval with Middle to Upper Triassic closure of the Paleotethys Ocean along a double subduction system, traced by the Kunlun-Anyemaqen suture to the north and the Jinsha-Litang suture to the south. New field, petrographic and geochemical data on Mesozoic plutons intrusive into Triassic metasediments of the eastern Songpan Ganze wedge are presented and integrated in a review of available data for the region. Three types of granitoids are distinguished: (i) high-K calc-alkaline granite to granodiorite (Yanggon, Maoergai, Markam, Sheng Meng, Xue Sheng, Taiyanghe, Menggu, Manai, Dusong Xian, Tagong and Jiulong plutons), (ii) high-K alkaline granite (Nyanbaoyeche and Rilong plutons and the Niuxingou shoshonitic syenite), and (iii) peraluminous S-type granite (Markam and Manai leucogranites). Elemental and isotopic signatures of these granitoids are consistent with the implication of both crustal (Yangtze craton, and Songpan Ganze metasediments) and mantle (asthenospheric mantle and metasomatised lithospheric mantle) sources. Based on (i) the ages of the plutons that are concomitant with the end of the northern and southern subductions of the Paleo-Tethys, (ii) the position of the plutons intrusive in the crustal tectonically accreted units decoupled from the downgoing plate of this double subduction system, (iii) the diversity of their petrological and geochemical signatures, we propose that magma emplaced in the Songpan Ganze accretionary-orogenic wedge were generated at the end of the Paleotethys closure in a context of slab retreat, accommodated by a tear fault along the passive margin of the South China block. Indeed, we argue that this context is the most favourable to trigger synchronous partial melting of (i) the suprasubduction enriched mantle wedge owing to lowering of the mantle solidus by metasomatism, (ii) the upwelled undepleted asthenospheric mantle into the tear fault owing to decompression, (iii) the metasomatized lithospheric continental mantle of the Yangtze craton owing to the temperature increase associated to the asthenospheric upwelling and (iv) the rocks of the Songpan Ganze accretionary wedge composed of metasediments and Yangtze continental margin basement owing to the combined effects of increased radioactive heat production and mantle heat flux. We propose that the concentration of plutons along the eastern margin of the Songpan Ganze results from focussed migration and emplacement of the granitic magmas guided by the development of a tear fault along the former passive eastern margin of the Yangtze craton as a consequence of the Paleotethys slab retreat.