太平洋北部铁锰结核富集区沉积物的元素地球化学特征

本文对太平洋北部铁锰结核富集区沉积物的元素地球化学作了较为详细的研究。因子分析提供的信息表明,元素的分布主要受三个因子控制:（1）粘土及Fe、Mn氧化物水化物胶体的吸附作用;（2）生物化学作用过程有关的自生沉积作用;（3）海底页岩风化及附近海区的火山喷发作用。元素的来源:（1）Fe、Mn、Cu、Co、Ni、Zn、Cr、Cr、Mg、Al、Ti、K共生,主要来自粘土吸附;（2）C_有机、N、Sr、Na及Si、Ca、Sr主要来自生物化学过程沉积;（3）Pb主要来源于岩石碎屑（火山喷发碎屑）。     

Geochemical and mineralogical properties of sulfide-bearing fine-grained sediments in Finland

 The geochemical and mineralogical characteristics of bulk samples and various size fractions of sulfide-bearing fine-grained sediments in the Petalax area, western Finland, were studied with ICP-AES (aqua regia digestion and "total" digestion) and X-ray diffraction. The sediments, which are dominated by particles <0.06 mm (clay and silt size), are composed of phyllosilicates (micas, kaolinite, chlorite, vermiculite), quartz, feldspars, amphiboles, organic matter, and secondary S minerals. The chemical analyses show that Na, Ca, and Sr are enriched in the silt and sand fractions, that Zr is enriched in the silt fraction, and that the concentrations of all other studied metals (Al, Ba, Co, Cr, Cu, Fe, K, La, Mg, Mn, Nb, Ni, Sc, Th, Ti, V, Y, and Zn) increase from the sand to the clay fraction. Sodium, Ca, and Sr occur largely in poorly dissolved feldspars, which explains the distribution of these metals in the sediments. The increase in the concentrations of most metals in the clay fraction is interpreted to be the result mainly of an increase in phyllosilicates in this size fraction. A geochemical comparison between the sulfide-bearing fine-grained sediments and glacial till shows that the former are enriched in several potentially toxic metals. It is therefore argued that the hydrological and ecological problems associated with the sulfide-bearing sediments are related not only to the production of acidity in oxidized layers, but also to mobilization and dispersion of toxic metals. Strategies to minimize damage of freshwater systems in areas covered with sulfide-bearing fine-grained sediments are suggested. Received: 20 February 1997 · Accepted: 25 August 1997     

Geochemistry of stream water in a catchment in Finland affected by sulphidic fine sediments

The impact of sediment type on stream water geochemistry was studied in a catchment in Finland affected by sulphidic fine-grained sediments. Stream water samples for general characterisation of water quality (pH, electrical conductivity) were taken at the basin outlet during various hydrological conditions, while samples for detailed geochemical analysis were collected at 119 sites in the catchment on one single occasion during high-water flow in autumn. The occurrence of sulphidic fine sediments was estimated based on data from an airborne electromagnetic survey carried out by the Geological Survey of Finland.Growing-symbol maps, which were prepared for each of the studied variables in water, and statistical calculations including factor analysis and Spearman correlations show that the concentrations of Al, Ga, U and Tl, all the lanthanides and several alkali and alkaline earth metals (K, Mg, Na, Li, Ca, Rb, Sr), transition metals (Cd, Co, Cu, Zn, Sc, Mn, Ni, Y, Hf) and non-metals (S, Br, I, Si) increase in water when the proportion of the catchment cover of sulphidic fine sediments increases. It is therefore argued that these elements are released and mobilised in considerable amounts by the oxidation and subsequent acidification and weathering of this type of sediment. Other elements are either slightly depleted in streams in areas of sulphidic fine sediments (V, Nb, Pb, Zr), have a distribution unrelated to sediment type (Fe, Cr, Cs, Mo), or are only weakly impacted by the occurrence of sulphidic sediments in the catchment (As, Ti, Ba). It is argued that these elements are not leached extensively from the oxidising sulphidic sediments, and that their distributions at least partly may be controlled by the contents of dissolved humic material and/or suspended organic and inorganic phases in the water.     

Evaluation of elemental enrichments in surface sediments off southwestern Taiwan

Surface slices of 20 sediment cores, off southwestern Taiwan, and bed sediment of River Kaoping were measured for major and trace elements (Al, As, Ca, Cd, Cl, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, Ti, V, and Zn) to evaluate the geochemical processes responsible for their distribution, including elemental contamination. Major element/Al ratio and mean grain size indicate quartz-dominated, coarse grained sediments that likely derived from sedimentary rocks of Taiwan and upper crust of Yangtze Craton. Bi-plot of SiO₂ versus Fe₂O₃^T suggests the possible iron enrichment in sediments of slag dumping sites. Highest concentrations of Cr, Mn, P, S, and Zn found in sediments of dumping sites support this. Correlation analysis shows dual associations, detrital and organic carbon, for Cr, P, S, and V with the latter association typical for sediments in dumping sites. Normalization of trace elements to Al indicates high enrichment factors (>2) for As, Cd, Pb, and Zn, revealing contamination. Factor analysis extracted four geochemical associations with the principal factor accounted for 25.1% of the total variance and identifies the combined effects of dumped iron and steel slag-induced C–S–Fe relationship owing to authigenic precipitation of Fe–Mn oxyhydroxides and/or metal sulfides, and organic matter complexation of Fe, Mn, Ca, Cr, P, and V. Factors 2, 3, and 4 reveal detrital association (Ti, Al, Ni, Pb, Cu, and V), effect of sea salt (Cl, Mg, Na, and K) and anthropogenic component (As and Zn)-carbonate link, respectively, in the investigated sediments.     

Spatial trends and losses of major and trace elements in agricultural acid sulphate soils distributed in the artificially drained Rintala area,W. Finland

Acid sulphate soils, common in the coastal areas of Finland, contribute strongly to high acid, S and metal loadings on adjacent surface waters. This, in turn, is causing significant harm to the aquatic ecology. There is, however, limited knowledge on the total amounts of acidity and chemical elements leached from these soils. The overall objective of this study was to determine geochemical patterns in acid sulphate soils and their parent sediments and, based on the identified patterns assess the extent, mechanisms and present state of leaching of major and trace elements from these soils. The distribution of pH, aqua regia extractable concentrations of P and metals (Al, Ba, Ca, Co, Cr, Cu, Fe, K, La, Mg, Mn, Na, Ni, Sr, Th, Ti, V, Zn) and total concentrations of S and C were determined in 30 vertical profiles collected in the 23 km² large Rintala agricultural area (mid-western Finland) underlain largely with S-rich sediments. It was found that approximately 70% of the area consists of acid sulphate soils with a minimum pH<4.0, an average depth of 1.8 m, and S concentrations in the parent sediments varying from 0.24 to 1.04%. Acid sulphate soils have not developed where the S concentrations in the sediments are ⩽0.10% or where the concentrations of organic C in the soil zones are >4%. Four different methods were used to estimate the losses of chemical elements from the acid sulphate soils: (1) the concentrations in the soil were compared with those in the parent sediments, (2) due to indicated heterogeneities in several profiles, the vertical changes of the immobile Ti was used to re-calculate element losses, (3) element depletions in the acid sulphate soils (as compared to those in the parent sediments) were compared to the corresponding depletions in the non acid sulphate soils, (4) element concentrations in drainage waters were compared with those in the parent sediments. Based on these calculations, it was assessed that the percentual leaching of the aqua regia extractable fraction (total for S) has been as follows: S (40–50%), Na (30–50%), Mn (25–35%), Sr (15–20%), Ca–Ni–Co (approximately 10%), Mg–K–Zn (5–10%), Th–La–Cu–Al–P–Ti–Fe (<5%), and Ba–Cr–V (<1%). While it was possible to quite accurately estimate the percentages and thus the amounts of elements lost, it was not possible to estimate the rate of leaching as there is no available detailed information on dates when ditching activities and thus oxidation-acidification processes started. Other calculations indicated that the mobile S reservoir is still some 15 ton/hectare, which is huge but still smaller than the losses that have occurred since the area was drained (23–28 ton/hectare).     

甘肃庄浪全新世黄土-古土壤序列元素分布特征及意义

通过对渭河上游XJN全新世剖面的Fe、Al、Si、K、Ca、Mg、Na、Ti和Sr元素含量的分析,发现这些元素的分布与气候密切相关。在剖面中表现为:迁移序列是Ca>Sr>Na>Mg,Fe、Al、Si、K和Ti则相对富集;Ca-Sr关系呈两段式分布,指示全新世早期的一次环境变化;Ki残积系数增大,Ca/Mg比值减小,指示化学风化作用增强。     

东营凹陷古近系中深层湖盆演化中的无机元素响应

为查明无机元素分布与水深、盐度等沉积环境以及湖盆演化过程的关系,采用电感耦合等离子体发射光谱仪分析对东营凹陷郝科1科探井古近系深层微量元素含量进行了测试、分析,所涉及的研究层位是该凹陷的主要烃源岩层段（沙河街组三亚段、沙河街组四亚段、孔店组）,分析结果表明:在水体浅、蒸发作用强烈的孔店组—沙四下亚段强氧化性滨浅湖环境里,钙、锶含量和Ca/Mg、Sr/Ba、Sr/Ca参数值具低值响应,铁、铝、钡、钒含量和（Fe+Al）/(Ca+Mg)参数值具高值响应;在沙四中亚段膏岩、盐岩等普遍发育的盐湖环境中,钠、锶含量和Sr/Ba、Fe/Mn、Sr/Ca均出现高值响应,锰、钡、钒含量和V/Ni、(Fe+Al)/(Ca+Mg)出现低值响应;在还原性的沙四上亚段半咸化深湖环境中,钾、钠、铁含量和Fe/Mn值具低值响应,钙、锰含量具高值响应;在沙四中亚段膏盐与泥岩共生体系中元素分布离散性明显,呈现波动性特征;Sr/Ba、Sr/Ca在盐湖环境中出现显著的高值响应,被证实可以作为良好的水体盐度指标参数,Fe/Mn、(Fe+Al)/(Ca+Mg)随水体加深逐渐增大,是良好的水体深浅指标参数。元素分布受沉积环境、岩性特征等多种地质因素的影响,在利用元素含量分布及特征元素比值来判断某单个地质因素的变化时,应该应用多种参数,进行综合判断。     

Geochemistry of the Cauvery Estuary,East Coast of India

Major ion chemistry of water and elemental geochemistry of suspended and surficial sediments collected from the Cauvery Estuary were studied to understand the geochemical processes in this tropical estuarine system. Specific conductance (EC), total dissolved solids (TDS), and total suspended matter (TSM) increased conservatively with increasing chlorinity. In general, SO₄ ^2?, Na, K, Ca, and Mg showed an increasing trend while H₄SiO₄ and PO₄ ^3? showed a decreasing trend toward the sea. Additional removal mechanisms operating for these ions in the Cauvery Estuary have been identified based on observed concentrations. Factor analysis pointed out the sources contributing to the observed trends in estuarine water chemistry. POC and PON decreased toward the high chlorinity zone. TSM in the Cauvery Estuary were mostly of inorganic nature. Stable carbon isotope values showed that the carbon was equally of marine and terrestrial origin and helped to delineate the contribution of river water and seawater. The ? mean size (a logarithmic grain size scale commonly used by sedimentologists) indicated that the surficial sediments were primarily comprised of coarse and silt, whereas suspended sediments were principally silt and clay. Suspended sediments were enriched in clays compared to surficial sediments. Quartz and feldspar were abundant among detritals while chlorite, kaolinite, and montmorillonite were dominant among clays. Silicon was the most abundant element in the sediments followed by Al, Ca, Na, K, Fe, Mn, and P. Heavy metals were enriched in the suspended sediments compared to the surficial bottom sediments as follows: Fe = 3.5, Mn = 7.4, Pb = 1.1, Zn = 15.2, Cu = 7.4, and Cr = 4.0. The levels of Cd, Cr, Zn, and Fe increased up the middle reaches and then decreased toward the sea due to urban effluent and fertilizer input. Size fractionation studies indicated that the metal concentration in the finer fraction was 50% higher by mass than the coarse silt and fine silt fractions. Chemical fractionation studies showed that the abundance of metals were in the order of residual > organic/sulfide > carbonate > Fe/Mn oxide > exchangeable fractions.     

Geochemistry of metals in sediments from the mainstem of the Yellow River, China

Sediment samples at 10 locations in the mainstem of the Yellow River were taken in 1994. Five forms (exchangeable, carbonate, organic, Fe/Mn oxide and residual) of metals were extracted by the Tessier method. The total contents and contents of the five forms of 16 metal elements (Li, Na, K, Ca, Sr, Ba, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Al) were determined by ICP-AES. In sediments of the Yellow River, except for Na, mobile elements (such as K, Ca) do not show a negative correlation with the immobile elements. Alkaline metals (Li, Na, and K), Ti, and Al exist mainly in the residual form. The exchangeable forms of alkaline-earth elements (Ca, Sr, and Ba) are the highest, and their residual forms go up with the increase of the period in the periodic table of elements. Half of Mn exists in the residual form, and its non-residual forms exist mainly in carbonate and oxide forms. Except Mn, the iron group elements (Fe, Co, Ni, V, Cr) mainly exist in the residual and oxide forms. High carbonate content of Ca does not cause high contents of other elements in carbonate form, showing that chemical weathering is not strong in the area.     

广东三水盆地古近系心组生油层的元素地球化学特征

沉积物的元素地球化学特征是对沉积盆地水体环境以及古气候条件变化的响应。本文根据元素（Al、Fe、Mg、Ca、K、Na、P、V、Ni、Co、Cr、Cu、Zn、Sr、Ba、Cd、Li、Mn、Pb、Ti）的含量及其比值（Al/Ti、Fe/Mn、Sr/Ba、Mg/Ca、Sr/Ca、Na/Ca、V/Cr、Ni/Co、Ni/V）的变化，对三水盆地古近系心组红岗段生油层的沉积条件进行了系统分析。心组红岗段下部（亚段A）表现为较稳定的地球化学特征。各元素丰度及其比值指示这一时期陆源输入持续较高、且物源组成变化不大。由于海水入侵的影响，湖盆水体盐度相对较高，底部水体以弱氧化条件为主，O₂-H₂S界面位于水/沉积物界面附近。红岗段中上部（亚段B、C）的元素地球化学特征变化较为频繁且幅度很大，反映古气候和湖盆沉积条件的迅速变迁。在潮湿气候条件下，沉积物的地球化学特征表现为以Al、Ti为代表的外源元素含量及其比值较高，而Mg、Ca等盆内化学沉积元素含量较低。古氧气指标指示底部水体为还原环境，有利于有机质保存。因而，相应于较高的有机碳含量。在间歇性干旱时期，陆源输入减少，外源元素含量及其比值显著降低。随着蒸发作用的加强，水体盐度加大，内源元素丰度以及Mg/Ca、Sr/Ba、Sr/Ca和Na/Ca比值大幅度上升。底部水体为氧化环境，O₂-H₂S界面多位于水/沉积物界面或沉积物中。上述两种气候条件在红岗段中上部沉积时期交替出现。红岗段沉积后期由于淡水的长期输入，湖水出现逐渐淡化趋势。     

Major and trace element geochemistry of the Bigadi? Borate deposit, Balikesir, Turkiye

This study investigates the major and trace element geochemistry of Bigadi borate deposits, the largest colemanite and ulexite deposits in the world. The known borate deposits of Turkiye were deposited in the lacustrine environment during Miocene when the volcanic activity occurred from Tertiary to Quaternary. All of the Turkish borate deposits are classified as volcanic related deposits. Boron ore deposits intercalated with claystone, mudstone, tufa and fine layered limestone show lens shape. Borate minerals formed in two zones. Tiilu and Acep-Simav open mines represented the lower and upper borate zones, respectively. Colemanite and ulexite are dominant minerals at all ore zones. The major elements of Bigadi borates contain Ca, Si, Mg, Al, Fe, S, Na, P and Mn at Tiilu, Ca, Na, Si, Mg, S, Al, P and Mn at Simav, and Ca, Na, Si, Mg, S, AI and Mn at Acep samples respectively. Except for Li, Mo, Sb, As, Sr and Se, concentrations of other trace elements are significantly lower than averages of earth crust and andesite at the three mines. With respect to averages of earth crust and andesite, Mo, Sr, As, Li and particularly Se are enriched significantly in the Bigadi. In examining depth-dependent variations of major and trace elements, four element groups at the Tiilu site and six element groups at the Simav and Acep sites were determined. Element abudances or element geochemical trends show differences at the Tülü, Simav and Acep mines. These differences can be explained by the diversity of physicochemical conditions in the deposition environment by the effect of differences at the recharge regime and source.     

Wide-spaced sampling of humus in fennoscandia

In support of IGCP Project 259 (International Geochemical Mapping), a pilot survey designed to test the effectiveness of analysing dried humus collected at an extremely low sampling density (one composite sample per 23 000 km²) for geochemical mapping was carried out in 49 large catchment basins in Fennoscandia. The samples were analysed for their aqua-regia leachable contents of 30 elements by ICP-ES. The results were compared with those of till sampled at the same sites and with moss from previous surveys. The correlation with underlying bedrock was also studied.Geological features exert only a weak influence on the regional distribution of elements in humus. Exceptions are high levels of Ca and Sr in areas of carbonate bedrock and low contents of K in areas of Archean rocks. The distribution patterns of Co, Cr, Cu, Mg, Ni and Zn in humus coincide partly, and the levels correlate positively with those in till. The contents of Ni, Cr and Cu are lower in humus overlying acid magmatic rocks and arkose than other rock types.Pollution is the obvious source of high concentrations of Pb, Cd and Zn in southern Sweden and southern Norway. Acid fallout seems to cause leaching of Al, P and La from the humus horizon. The contents of these elements are low in the south where deposition of S and N is high and pH of rainwater is below 4.5. Deposition of sea salts gives high levels of Na, Mg, K and B along the coast of Norway and southern Sweden.The contents of several elements in humus correlate positively with the amount of organic matter (LOI). Comparison between four types of forest shows that the contents of Ca, Mg and Na in birch forest and of Cd, Mn, Pb and Zn in spruce forest are significantly higher than in other forest types. These features, however, are considered false and are due to sources such as atmospheric deposition of anthropogenic metals and sea salt.The results of the relatively strong chemical attack used for analyses of humus samples are less informative than those from till and overbank sediments. A weaker attack may have given more useful information. The humus horizon could be suited for environmental monitoring if used in global geochemical mapping.     

吉林蛇纹石玉特征初步研究

对产自吉林省白山市抚松县沿江乡的蛇纹石玉样品分别从地质背景、激光诱导离解光谱、X射线粉末衍射和红外吸收光谱等方面进行了研究,并与辽宁岫玉样品进行了对比。结果表明,吉林蛇纹石玉样品的主要颜色为深浅不一的绿色,主要含Si,Al,Cr,Fe,Mn,Mg,Ca,Sr和Na等元素,其中Ca与Mg的谱线较强,Al,Mn与Sr的质量分数少;X射线粉末衍射结果显示,样品的主要矿物组成为纤蛇纹石,红外光谱结果也显示了其具有纤蛇纹石峰值的特征。     

Geochemical characteristics of elements in suspended sediments in the Huanghe (Yellow) River

Eighteen suspended sediment samples were collected along the Huanghe River main stem from upper reaches on the Qinghai-Tibet Plateau (Tibet Plateau) to the entrance at the Bo Hai Bay and at confluences of its tributaries, during the first summer flood in 1980. Major elements such as Si, Al, Fe, Ca, Mg, K, Na, and trace elements such as As, Ba, Cd, Ce, Co, Cr, Cu, Ga, Hg, Li, Mn, Mo, Ni, P, Pb, Se, Sn, Sr, Ti, V, Zn and humus were examined. Variations in composition of suspended sediments also were studied. Three major types of sediment composition were observed. The controlling factor for the variation is parent rocks, though climate and vegetation played an active role. Correlation coefficients, cluster analysis, and enrichment factors were calculated to study the geochemical characteristics of the sediments. Mg, Na and Fe were the only ones subject to considerable leaching, whereas Se, Cd, Zn were significantly accumulated, indicating a low intensity of weathering.     

一种新的闪石共存对—铁闪石与铁韭闪石对

新近在我国山西省娄烦县尖山铁矿的角闪片岩中发现一种取向连生的镁铁质闪石与钙质闪石共存对。电子探针分析确定它们分别为铁闪石Ｋ０．００１（Ｎａ０．０２７Ｃａ０．０７３Ｍｎ０．０３１Ｆｅ＾２＋１．８０１）１．９３２（Ｆｅ＾２＋２．９４８Ｍｇ１．９６４Ｔｉ０．００２Ａｌ０．０８７）５Ｓｉ８．０６９Ｏ２２．１０（ＯＨ）２与铁韭闪石（Ｋ０．１３５Ｎａ０．４６１）０．５９６（Ｎａ０．０８８Ｃａ１．８５３Ｍｎ０．     

Geochemistry of ferromanganese nodule–sediment pairs from Central Indian Ocean Basin

Fourteen ferromanganese nodule–sediment pairs from different sedimentary environments such as siliceous ooze (11), calcareous ooze (two) and red clay (one) from Central Indian Ocean Basin (CIOB) were analysed for major, trace and rare earth elements (REE) to understand the possible elemental relationship between them. Nodules from siliceous and calcareous ooze are diagenetic to early diagenetic whereas, nodule from red clay is of hydrogenetic origin. Si, Al and Ba are enriched in the sediments compared to associated nodules; K and Na are almost in the similar range in nodule–sediment pairs and Mn, Fe, Ti, Mg, P, Ni, Cu, Mo, Zn, Co, Pb, Sr, V, Y, Li and REEs are all enriched in nodules compared to associated sediments (siliceous and calcareous). Major portion of Si, Al and K in both nodules and sediments appear to be of terrigenous nature. The elements which are highly enriched in the nodules compared to associated sediments from both siliceous and calcareous ooze are Mo – (307, 273), Ni – (71, 125), Mn – (64, 87), Cu – (43, 80), Co – (23, 75), Pb – (15, 24), Zn – (9, 11) and V – (8, 19) respectively. These high enrichment ratios of elements could be due to effective diagenetic supply of metals from the underlying sediment to the nodule. Enrichment ratios of transition metals and REEs in the nodule to sediment are higher in CIOB compared to Pacific and Atlantic Ocean. Nodule from red clay, exhibit very small enrichment ratio of four with Mn and Ce while, Al, Fe, Ti, Ca, Na, K, Mg, P, Zn, Co, V, Y and REE are all enriched in red clay compared to associated nodule. This is probably due to presence of abundant smectite, fish teeth, micronodules and phillipsite in the red clay. The strong positive correlation (r ? 0.8) of Mn with Ni, Cu, Zn and Mo and a convex pattern of shale-normalized REE pattern with positive Ce-anomaly of siliceous ooze could be due to presence of abundant manganese micronodules. None of the major trace and REE exhibits any type of inter-elemental relationship between nodule and sediment pairs. Therefore, it may not be appropriate to correlate elemental behaviour between these pairs.     

Suspended basaltic glass–seawater interactions

The objective of this study was to quantify by experiments the initial seawater–suspended basaltic glass interactions following the 1996 outburst flood from the Vatnajökull glacier, Iceland. The altered basaltic glass dissolved in seawater as recorded by the Si release from the glass. The dissolved concentrations of Na, Ca, Si, Ba, Cd, Co, Cu, Hg, Mn, Ni and total dissolved inorganic N increased with time but the concentrations of Mg, K, S, Sr, Fe, Pb and Zn decreased. Calculated 1 to 10 day fluxes for Si range from 38,000 tons/day to 70,000 tons/10 days. The fluxes for other major elements are more uncertain, but the positive flux (release from suspended matter to seawater) of Ca and Na, and negative flux of Mg, K and S are greater than the Si flux.     

The Determination of Major Oxide and Trace Element Concentrations in Eighteen Chinese Standard Reference Samples by X-ray Fluorescence Spectrometry

Eighteen Chinese geologic reference samples (stream sediments GSD 9–12, soils GSS 1–8, and rocks GSR 1–6) were analyzed by wavelength-dispersive X-ray fluorescence spectrometry (XRFS) for major elements Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P, and by energy-dispersive XRFS for trace elements Ba, Ce, Cr, Cu, La, Nb, Ni, Rb, Sr, Y, Zn, and Zr. Major element analysis followed gravimetric determination of loss on ignition, and samples were prepared by fusion with Li₂B₄O₇. A loose-powder sample preparation was used for trace element analysis. The results reported in this study are, generally, in good agreement with concentrations compiled by X. Xie of the Geochemical Standard Reference Group and the Institute of Geophysical and Geochemical Exploration (People's Republic of China).     

Manganese-rich brown layers in Arctic Ocean sediments: Composition, formation mechanisms, and diagenetic overprint

We present inorganic geochemical analyses of pore waters and sediments of two Late Quaternary sediment cores from the western Arctic Ocean (southern Mendeleev Ridge, RV Polarstern Expedition ARK-XXIII/3), focussing on the composition and origin of distinct, brown-colored, Mn-rich sediment layers. Carbonate enrichments occur in association with these layers as peaks in Ca/Al, Mg/Al, Sr/Al and Sr/Mg, suggesting enhanced input of both ice-rafted and biogenic carbonate. For the first time, we show that the Mn-rich layers layers are also consistently enriched in the scavenged trace metals Co, Cu, Mo and Ni. Distinct bioturbation patterns, specifically well-defined brown burrows into the underlying sediments, suggest these metal enrichments formed close to the sediment-water interface. The geochemical signature of these metal- and carbonate-rich layers most probably documents formation under warmer climate conditions with an intensified continental hydrological cycle and only seasonal sea ice cover. Both rivers and sea ice delivered trace metals to the Arctic Ocean, while enhanced seasonal productivity exported reactive organic matter to the sea floor. The coeval deposition of organic matter, Mn (oxyhydr)oxides and trace metals triggered intense diagenetic Mn cycling at the sediment-water interface. These processes resulted in the formation of Mn and trace metal enrichments, and the degradation of labile organic matter. With the onset of cooler conditions, reduced riverine runoff and/or a solid sea ice cover terminated the input of riverine trace metal and fresh organic matter, resulting in deposition of grayish-yellowish, metal-poor sediments. Oxygen depletion of Arctic bottom waters under these cooler conditions is not supported by our data, and did not cause the sedimentary Mn distribution. While the original composition and texture of the brown layers resulted from specific climatic conditions and corresponding diagenetic processes, pore water data show that diagenetic Mn redistribution is still affecting the organic-poor deeper sediments. Given persistent steady state conditions, purely authigenic Mn-rich brown layers may form, while others may be partly or completely dissolved. The degree of diagenetic Mn redistribution largely depends on the depositional environment, the Mn and organic matter availability, and apparently affected the Co/Mo ratios of Mn-rich layers. Thus, brown Arctic layers are not necessarily synchronous features, and should not be correlated across the Arctic Ocean without additional age control.     

贵州威宁窑上组沉积物物源特征及沉积控制因素分析

根据威宁草海第四纪窑上组沉积物主量元素和REE特征,探讨沉积物物源特征、气候演变情况、沉积物堆积控制因素。结果表明:Al、Mg、Ca、K、Na和Ti的含量变化在剖面上一致,它们的相关系数很高(0.522~0.985)。Fe含量和Mn含量呈正相关形式,与Al、Mg、Ca、K、Na和Ti呈负相关。Fe2O3含量在土黄色粘土的铁质层很高(42.86%~50.57%)。样品中REE球粒陨石标准化配分模式与贵州土壤、贵州碳酸盐岩风化壳配分模式很相似,与峨眉山玄武岩配分模式不一致,但其含量略低于贵州碳酸盐岩风化壳的含量;沉积物主要来源于碳酸盐岩,且碳酸盐岩强烈风化成土作用使REE超常富集,在剖面上呈现高ΣREE(平均219.38μg/g)。通过Mg/Ca、MgO/Al2O3、(CaO+K2O+Na2O)/Al2O3、(Fe2O3+Al2O3)/(MgO+CaO)、(K+Na+Ca+Mg)/(Fe+Mn)、(Al+Fe+Mn)/(K+Ca+Mg)和(MgO+Na2O+CaO)/Al2O3等气候指标研究,表明在草海窑上期为湖泊沉积时期,气候经历了由温暖湿润向冷干的转变。同时,认为物源性质、构造运动、气候等共同控制该区沉积物形成。