中印度洋海盆表层沉积物稀土元素分布特征及富集规律

对中印度洋海盆14个站位的表层沉积物进行了稀土元素(REE+Y,简称REY)分布特征和富集规律研究.结果表明,样品中REY主要富集于沸石黏土和远洋黏土中(稀土元素总量最高为1239×10?6),且明显富集钇(Y)等重稀土元素(Y富集系数高达14.1,重稀土元素和Y富集系数最高为11.6);富稀土沉积物呈明显Ce亏损,发...     

Physical Properties, Morphology and Petrological Characteristics of Pumices from the Central Indian Ocean Basin

About 400 pumice clasts collected from the Central Indian Ocean Basin(CIOB)were studied for their morphology and were classified based on their shape and size.A majority of the samples range between<1 cm and 36 cm and in the Zinggs shape diagram plot in the equant and oblate fields.The Corey Shape Factor for most of the samples is close to 0.7,which is common for volcaniclastic material. The physical properties such as density,specific gravity,void ratio,porosity,moisture content and degree of saturation...     

Relationship between chemical composition and magnetic susceptibility in sediment cores from Central Indian Ocean Basin

Three sediment cores in a north-south transect (3°N to 13°S) from different sediment types of the Central Indian Ocean Basin (CIOB) are studied to understand the possible relationship between magnetic susceptibility (χ) and Al, Fe, Ti and Mn concentrations. The calcareous ooze core exhibit lowest χ (12.32 × 10⁻⁷ m³ kg⁻¹), Al (2.84%), Fe (1.63%) and Ti (0.14%), terrigenous clay core with moderate χ (29.93 × 10⁻⁷ m³ kg⁻¹) but highest Al (6.84%), Fe (5.20%) and Ti (0.44%), and siliceous ooze core with highest χ (38.06 × 10⁻⁷ m³ kg⁻¹) but moderate Al (4.49%), Fe (2.80%) and Ti (0.19%) contents. The distribution of χ and detrital proxy elements (Al, Fe, and Ti) are identical in both calcareous and siliceous ooze. Interestingly, in terrigenous core, the behaviour of χ is identical to only Ti content but not with Al and Fe suggesting possibility of Al and Fe having a non-detrital source. The occurrence of phillipsite in terrigenous clay is evident by the Al-K scatter plot where trend line intersects K axis at more than 50% of total K suggesting excess K in the form of phillipsite. Therefore, the presence of phillipsite might be responsible for negative correlation between χ and Al (r = −0.52). In siliceous ooze the strong positive correlations among χ, Al_exc and Fe_exc suggest the presence of authigenic Fe-rich smectite. High Mn content (0.5%) probably in the form of manganese micronodules is also contributing to χ in both calcareous and siliceous ooze but not in the terrigenous core where mean Mn content (0.1%) is similar to crustal abundance. Thus, χ systematically records the terrigenous variation in both the biogenic sediments but in terrigenous clay it indirectly suggests the presence of authigenic minerals.     

Biogenic signature and ultra microfossils in ferromanganese nodules of the Central Indian Ocean Basin

Theories related to the precipitation mechanism of the metallic elements in marine manganese nodules have remained controversial between two schools of thoughts (1) chemical oxidation (abiotic origin) and (2) deposition of the metals through microbial enzymatic processes (biogenic origin). One of the most important evidence in support of the biogenic origin is the occurrence of fossilized microbes. However, well-documented literature in this regard is either lacking or very scanty in case of Indian Ocean nodules. Using high resolution FEG-SEM we have recorded various biogenic signatures and ultra microfossils in the ferromanganese nodule samples from Central Indian Ocean Basin (CIOB) that are presented in this paper. The microfossils are mostly protozoans belonging to varieties of bacteria, diatoms and foraminifera. Some of the features recorded in this study have perhaps never been reported before from any manganese nodules. The chemical compositions of these ultra microfossils indicate a high-level of manganese precipitation in and around them in comparison to the distant surrounding areas. While clumpy microbes are enriched with nickel, the rod shaped bacteria are rich in copper. Up to 4.70 wt.% nickel and 5.31 wt.% Cu have been recorded in the fossilized microbe bodies. The high abundance of biogenic features as well as microfossils in the ferromanganese nodules and their chemical compositions support arguments in favor of a dominant role of the microorganisms in the construction of the nodules of the CIOB.     

Biological productivity, terrigenous influence and noncrustal elements supply to the Central Indian Ocean Basin: Paleoceanography during the past ∼ 1 Ma

A 2m-long sediment core from the siliceous ooze domain in the Central Indian Ocean Basin (CIOB; 13‡03′S: 74‡44′E; water depth 5099m) is studied for calcium carbonate, total organic carbon, total nitrogen, biogenic opal, major and few trace elements (Al, Ti, Fe, K, Mg, Zr, Sc,V, Mn, Cu, Ni, Zn, Co, and Ba) to understand the productivity and intensity of terrigenous supply. The age model of the sediment core is based on U-Th dating, occurrence of Youngest Toba Tuff of ∼ 74 ka and Australasian microtektites of ∼ 770 ka. Low carbonate content (< 1%) of sediment core indicates deposition below the carbonate compensation depth. Organic carbon content is also very low, almost uniform (mean 0.2 wt%) and is of marine origin. This suggests a well-oxygenated bottom water environment during the past ∼ 1100ka. Our data suggest that during ∼ 1100 ka and ∼ 400 ka siliceous productivity was lower, complimented by higher supply of terrigenous material mostly derived from the metasedimentary rocks of High Himalayan crystalline. However, during the last ∼ 400 ka, siliceous productivity increased with substantial reduction in the terrigenous sediment supply. The results suggest that intensity of Himalayan weathering, erosion associated with monsoons was comparatively higher prior to 400 ka. Manganese, Ba, Cu, Ni, Zn, and Co have around 90% of their supply from noncrustal (excess) source and their burial to seafloor remained unaffected throughout the past ∼ 1100 ka.     

The effect of grain size on the Cu, Pb, Ni, Cd speciation and distribution in sediments: a case study of Dongping Lake, China

This paper examines the surface sediments collected from Dongping Lake in China for speciation and distribution of toxic heavy metals (Cu, Pb, Ni, Cd) in different grain size fractions, and for the factors that need to be considered in potential hazard of metals to the environment. Four grain size fractions (<63, 63–78, 78–163 and 163–280 μm), divided in wet condition, and bulk samples less than 280 μm in diameter were analyzed for their distribution, density and appearance. A three-stage extraction procedure following the BCR protocol was used to chemically fractionate metals into “acid soluble”, “reducible”, “oxidizable” and “residual” fractions. Correlation analysis was used to analyze the datasets. The results showed that <63 μm grain size part constitutes the major proportion of the sediments, but its density is the smallest among the four grain size fractions. In general, the metal content curve against grain size presents “S” distribution, and the highest concentrations do not exist in <63 μm grain size. Appearance observation indicates that the adsorbed substance increases gradually along with the decreasing grain size. The dominant speciation of elements and the extent of pollution are responsible for the metal distribution in different grain size sediments. While studying bioavailability and mobilization of metals, it is advisable to take metal speciation, grain size distribution and density into consideration.     

Natural gas sources, migration and accumulation in the shallow water area of the Panyu lower uplift: An insight into the deep water prospects of the Pearl River Mouth Basin, South China Sea

Although no drilling has been carried out in the deep water area of the Baiyun sag in the Pearl River Mouth Basin, South China Sea, the successful exploration for natural gas in the shallow water area of the Panyu lower uplift allows an insight into the prospectivity of the adjacent deep water fan system of the Baiyun sag. The Paleogene gas kitchen in the Baiyun sag provided both oil-derived gas and coal-derived gas. Fluid inclusion measurements and 2D numeric modelling of formation pressure indicate four episodes of hydrocarbon charge since the third release of the overpressure system. Seismic wipeout zones manifest several types of gas chimney which could play a role in vertical migration conduits to feed the natural gases into the deep water fan system. There would be, therefore, a low risk for hydrocarbon exploration in the deep water fan system.     

Magnetic signature of heavy metals pollution of sediments: case study from the East Lake in Wuhan,China

Detailed magnetic measurements and geochemical analyses were performed on 114 sediment samples collected from the East Lake, Wuhan city, China, to establish a possible link between the enhanced concentration of anthropogenic magnetic particles and heavy metals with known sources. Relatively higher magnetic susceptibility values (mass-specific, χ, >150 × 10⁻⁸ m³ kg⁻¹) were observed for samples near the pollution sources: e.g. the Wuhan Iron and Steel Company (WISC), the Qingshan Thermal Power Plant (QTPP), the banks (driveways) of the lake and near the sightseeing route of yachts on the lake. Moreover, χ is positively correlated to the concentration of Pb (correlation coefficient r = 0.682), but negatively or weakly correlated with both Zn and Cu. In contrast, anhysteretic remanent magnetization (ARM) is significantly correlated with these major heavy metals (r = 0.645 for Zn–ARM, 0.699 for Pb–ARM and 0.841 for Cu–ARM, respectively), which indicate that ARM serves a better indicator for the pollution of heavy metals in this lake. Thermomagnetic analysis combined with magnetic hysteresis measurements revealed that magnetites in the pseudo-single-domain/multidomain grain-size regions are dominant. Scanning electron microscopy and energy dispersive X-ray examinations of the magnetic extracts showed that these Fe-rich particles have different morphologies: orange-peel structure, hollow structure with adhered smaller particles, Zr-rich melted-like irregular particles, pear-shaped spherules and spherules with slick surfaces. These features are typical for particles produced by anthropogenic activities. Because of the genetic relationship between the environmental setting of the East Lake and the nearby pollution sources, this study suggests that in situ magnetic surveys are sensitive to evaluate the environmental pollution on the lake bottom.     

Standardization of metal concentrations in sediments using regression residuals: an example from a large lake in Florida, USA

 A new method of standardizing metal concentrations in sediments was tested on samples from Lake Miccosukee, a large karstic lake in north Florida. Metal concentrations were analyzed in 222 sediment samples from 26 cores representing 9 sampling sites in the lake. Measured sedimentation rates in the lake are low. Percent organic matter strongly increases upward in all the cores. The C/N ratio remains constant throughout all the samples, with a mean value of about 13, regardless of depth or location. All of the geochemical variables are at least approximately log-normally distributed; thus, log-log or semi-log scattergrams were used and the data were log-transformed before statistical calculations were performed. Some elements (Mn, Zn, Hg, Cu, and Ca) are primarily associated with the organic fraction; others (La, Cr, Sr, and Ba) are clearly related to the terrigenous fraction; others show affinities for both fractions. Consequently, no bivariate scattergrams or plots of ratio versus depth – commonly used for standardization by plotting or ratioing a reference element (such as Al) to an element of interest – were found to be adequate for standardization of this dataset. The best method for standardization was found to be one based on multivariate (trivariate) linear regression, using log Al and log C as the independent variables (reference elements representing terrigenous and organic fractions, respectively), and the log of the element of interest as the dependent variable. Residuals (deviations) from the best-fit linear surface were then plotted versus depth in the cores to accomplish the standardization. The results indicate that, with the possible exception of Mn at two sites, there is little evidence of anthropogenic input of trace elements to the lake, and most trace-element concentrations in the lake can be considered as valuable baseline information. A significant finding is that different and erroneous conclusions might have been reached if other standardization methods, not based on trivariate regression, had been employed. Received: 28 August 1997 · Accepted: 24 November 1997     

渭河盆地始新世-渐新世沉积物源变化的钻探样品Sr和Nd同位素证据

始新世暖期和始新世-渐新世降温阶段（EOT）在地球气候系统演化中具有代表性,对认识现代全球变暖过程和机制有参考价值。渭河盆地堆积了始新世以来连续的河湖相沉积序列,对其进行沉积物源示踪研究有助于重建渭河流域地貌演化、沉积过程和气候环境变化。本研究对渭河盆地新生代沉积中心固市凹陷荔参1井（钻探井深6535 m）下部的始新世红河组（6527~5529 m）和渐新世白鹿塬组（5315~4759 m）样品进行了Sr和Nd同位素分析,探索古近纪渭河盆地的物源变化过程。结果显示,红河组样品Sr和Nd同位素平均值分别是⁸⁷Sr/⁸⁶Sr=0.716127和ε_Nd=-13.5,白鹿塬组Sr和Nd同位素平均值分别是⁸⁷Sr/⁸⁶Sr=0.720461和ε_Nd=-12.4。分粒级（< 2 μm,2~64 μm和>64 μm）Sr和Nd同位素测试结果表明,粒度效应对渭河盆地始新世-渐新世沉积物硅酸盐矿物的Sr同位素值影响较大,而对Nd同位素影响较小,表明硅酸盐矿物Nd同位素值可作为渭河盆地沉积物物源的指示。结合潜在源区Sr和Nd同位素分布特征,发现渭河盆地始新世和渐新世沉积物主要来自于秦岭造山带和鄂尔多斯地块的贡献,其物源变化与构造抬升和气候演变密切相关。渭河盆地始新世和渐新世沉积物传输和堆积过程与晚新生代相似,具有相对稳定的两端元物源,为利用红河组和白鹿塬组沉积序列重建古气候古环境奠定了良好的基础。

     

Heavy metal pollution in freshly deposited sediments of the Yamuna River (the Ganges River tributary): a case study from Delhi and Agra urban centres, India

 The Yamuna River sediments, collected from Delhi and Agra urban centres, were analysed for concentration and distribution of nine heavy metals by means of atomic adsorption spectrometry. Total metal contents varied in the following ranges (in mg/kg): Cr (157–817), Mn (515–1015), Fe (28,700–45,300), Co(11.7–28.4), Ni (40–538), Cu (40–1204), Zn (107–1974), Pb (22–856) and Cd (0.50–114.8). The degree of metal enrichment was compared with the average shale concentration and shows exceptionally high values for Cr, Ni, Cu, Zn, Pb and Cd in both urban centres. In the total heavy metal concentration, anthropogenic input contains 70% Cr, 74% Cu, 59% Zn, 46% Pb, 90% Cd in Delhi and 61% Cr, 23% Ni, 71% Cu, 72% Zn, 63% Pb, 94% Cd in Agra. A significant correlation was observed between increasing Cr, Ni, Zn, and Cu concentrations with increasing total sediment carbon and total sediment sulfur content. Based on the Müller's geoaccumulation index, the quality of the river sediments can be regarded as being moderately polluted to very highly polluted with Cr, Ni, Cu, Zn, Pb and Cd in the Delhi and Agra urban centres. The present sediment analysis, therefore, plays an important role in environmental measures for the Yamuna River and the planning of these city centres. Received: 21 June 1999 · Accepted: 1 October 1999     

Transport and sediment–water partitioning of trace metals in acid mine drainage: an example from the abandoned Kwangyang Au–Ag mine area, South Korea

Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid (0.1 N HCl) extraction, strong acid (HF–HNO₃–HClO₄) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump upstream of Chonam-ri creek. The sediment–water distribution coefficients (K _d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd. K _d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure. This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable forms of trace metals in natural stream sediments.     

Arsenic Levels in Groundwater from Quaternary Alluvium in the Ganga Plain and the Bengal Basin, Indian Subcontinent: Insights into Influence of Stratigraphy

Late Quaternary stratigraphy and sedimentation in the Ganga Alluvial Plain and the Bengal Basin have influenced arsenic contamination of groundwater. Arsenic contaminated aquifers are pervasive within lowland organic rich, clayey deltaic sediments in the Bengal Basin and locally within similar facies in narrow, entrenched river valleys within the Ganga Alluvial Plain. These were mainly deposited during early-mid Holocene sea level rise. Arsenic was transported from disseminated sources as adsorbed on dispersed phases of hydrated-iron-oxide. These were preferentially entrapped as sediment coatings on organic-rich, fine-grained deltaic and floodplain sediments. Arsenic was released later to groundwater mainly by reductive dissolution of hydrated-iron-oxide and corresponding oxidation of sediment organic matter. Strong reducing nature of groundwater in the Bengal Basin and parts of affected middle Ganga floodplains is indicated by high concentration of dissolved iron (maximum 9-35 mg/l). Groundwater being virtually stagnant under these settings, released arsenic accumulates and contaminates groundwater. The upland terraces in the Bengal Basin and in the Central Ganga Alluvial Plain, made up of the Pleistocene sediments are free of arsenic contamination in groundwater. These sediments are weakly oxidised in nature and associated groundwater is mildly reducing in general with low concentration of iron (<1 mg/l), and thus incapable to release arsenic. These sediments are also flushed free of arsenic, released if any, by groundwater flow due to high hydraulic head, because of their initial low-stand setting and later upland terraced position.     

The intermediate step in fractionation trends of mildly alkaline volcanic suites: An experimental insight from the Pavin trachyandesite (Massif Central,France)

We examined magma storage conditions and eruptive dynamics for the trachyandesite (~58 wt% SiO₂, 9–10 wt% alkalis) of the Pavin monogenetic volcano, a maar-like explosive crater belonging to a small group of youngest volcanoes in the Massif Central. By confronting the natural samples to experimental products, we constrained pre-eruptive conditions around 950–975 °C, 150–200 MPa (~5.5–7.0 km in depth), NNO+1.5, and 4.5–5.5 wt% melt H₂O. There is petrological evidence of magma crystallization in the conduit up to shallow levels (~50 MPa; 2 km in depth) before fragmentation into pumice clasts in the last kilometre of ascent. The experiments highlight the role of biotite and of crystallization pressure in defining separate compositional trends of residual liquids, i.e. alkaline (trachytes) versus sub-alkaline (dacite-rhyolite).     

河流相沉积的河型转换特征与控制因素及其油气地质意义 ——以南苏丹Melut盆地Ruman地区坳陷期Jimidi组为例

河流相砂体是陆相含油气盆地的重要储层类型,其河型的时空转换不仅是研究盆地演化的直接证据,更是精准评价与预测油气储层的核心内容,已成为近年来国内外沉积研究的热点之一.以Melut盆地Ruman地区坳陷期Jimidi组为例,通过开展层序划分、岩相类型与岩相组合分析、高分辨率储层反演、以及砂体平面展布分析,结果表明:1)坳陷...     

同层型气钾复合矿藏的形成机理浅析:以四川盆地磨溪背斜中三叠统雷口坡组富钾卤水矿为例

四川盆地中三叠统雷口坡组中发育多种类型的钾盐矿藏,是我国找钾的重点目标层系。磨溪气田雷口坡组地层卤水富含K、Li、Br、B元素,定性为中低矿化度KCl、LiCl、Br^-、B₂O₃等超标的优质化工原料水,显示出较好的钾盐勘探前景。地震资料解释结果表明,磨溪气田雷口坡组一段的第一亚段(雷一¹)顶面表现为一个完整的长轴背斜形态,断层不发育。富钾卤水发育在背斜的翼部,而天然气则占据了背斜的核部,二者共同贮存在雷一¹亚段溶蚀孔洞发育的滩相白云岩中,构成了典型的同层型气钾复合矿藏。借鉴含油气系统的概念,将富钾卤水的形成、聚集及后期保存等影响卤水型钾矿形成全过程的各种因素总结归纳为6大关键要素,即钾的物质来源,储层物性、封盖条件、圈闭条件、运移方式和保存条件。在乐山—龙女寺古隆起形成和演化的背景下,确定构造圈闭形成时间,分析优质储层发育有利因素以及后期保存条件,并按照各要素在时空上的搭配关系,动态地分析雷口坡组同层型气钾复合矿藏的形成过程。烃类物质和卤化物都是地下水所含的特殊物质,在地下水动力场的作用下,地层水在雷口坡组内部向着川中地区的继承性发育的古构造高点——磨溪背斜持续运移。被运移而来的由蒸发浓缩的古海水和石膏脱水形成的初始富钾地层水不断捕获下伏绿豆岩释放的钾离子,使得钾离子二次富集成藏。在地层水运移和气藏压力的共同作用下,形成气在上、富钾卤水在下的复合矿藏。长期继承性发育的古隆起不仅是油气聚集的有利部位,亦是二次运移、聚集的富钾卤水矿藏发育部位。本次研究成果为四川盆地及其他类似盆地的“气钾兼探”工作提供了一种新的方法和思路。