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1.
In this study, we utilized environmental magnetic in combination with sedimentological and hydrodynamic data to investigate the formative processes of mudbanks along southwest coast of India. We document the linkages between enrichment of silt-sized magnetic particles and formation processes of mudbanks along Alappuzha coast. A trend of increasing magnetite concentration and coarsening in magnetic grain size is observed at mudbank stations M2 and M3, while the mud-deficient station (M1) showed an opposite trend. A strong relationship between magnetic and physical grain size for all samples implies that the magnetic particle size and clastic grain size are largely adjunct. Analysis of rock magnetic and grain size data of surficial and suspended sediments from non-mudbank (M1) and two mudbank stations (M2, M3) reflect the differential sediment partitioning and transport regimes which controlled the formation of mudbanks along Alappuzha coast. Two plausible mechanisms responsible for the formation of mudbanks are identified: grain size-selective entrainment is the dominant process during pre-monsoon; weaker hydrodynamics (waves and bottom currents) favors accumulation of silt-sized (fine and coarse) magnetic and non-magnetic fractions resulting in the formation of magnetically low-enriched sediment bed of mixed grain sizes. At the onset of monsoon, wave-induced energetic bottom currents enhance the suspension of entire sediment bedload at stations M2, M3 to form fluid mud. Concurrently, mineral-density-based selective fractionation allows the settling of coarse silt-sized magnetic particles, while the fine magnetic silt-size particles accumulate forming thick fluid mud as a suspension load resulting in the formation of mudbanks. An observed increase in magnetic susceptibility and coarsening in magnetic grain size of surficial sediments at mudbank stations (M2, M3) during monsoon period supports the interpretation. Our findings are summarized in a conceptual model which can be very well applied to investigate sediment dynamics associated with mudbank formation in coastal and shelf sedimentary systems.  相似文献   

2.
Heavy mineral analysis was carried out for the beach and fore dune sediments along 60 transects of Nizampatnam-Lankavanidibba coastal area. The heavy mineral assemblage in this area with decreasing abundance of opaques (Ilmenite + magnetite, 47.67%), pyriboles (20.35%), garnets (3.66%), epidote (3.23%) and with less than 3.0% concentration of sillimanite, zircon, staurolite, kyanite, apatite, spinel, monazite, biotite, topaz, leucoxene and chlorite. The heavy mineral concentrations are high in the finer fractions i.e., +120 and +230 (ASTM) than the coarse fraction (+60) of sand. In the seven sectors, heavy mineral assemblage is same but their concentrations are different. The sectors nearer to the river mouth contain high concentration of high specific gravity heavy minerals (ilmenite and magnetite) than sectors away from the river mouth. The redistribution of heavy minerals is controlled by creek dynamics, longshore currents, size and specific gravity of the heavy minerals.  相似文献   

3.
This study examined grain‐size distributions to address questions regarding geological and oceanographic controls on island morphodynamics along one of the longest undeveloped, mixed‐energy barrier island systems in the world. In particular, statistical analyses (i.e. analysis of variance, Tukey honest significant difference multiple comparison tests, nonparametric statistics and linear regression analysis) of 230 barrier island samples from Ocean City Inlet, Maryland, to the mouth of the Chesapeake Bay and 134 nearshore samples (d ≤ 10 m) identified grain‐size trends related to the morphodynamic characteristics of these systems. In general, the Virginia barrier islands north of Wachapreague Inlet and Assateague Island form a statistically different subset of grain sizes (medium‐grained to coarse‐grained sand) from the islands south of Wachapreague Inlet (fine‐grained sand). These textural trends corroborate the Pleistocene headlands of the Delmarva coastal compartment as the sediment source and indicate that some of the coarse‐grained to medium‐grained sediment bypasses the large sinks in the net southward longshore sediment transport system (i.e. Fishing Point and Chincoteague Inlet). This research also demonstrates that the preferential accumulation of coarse‐grained to medium‐grained sand on the ebb‐tidal delta at Wachapreague Inlet probably controls the erosional morphodynamics of the islands located downdrift (south) of the inlet. These results suggest that an increase in tidal prism, set up by sea‐level rise and/or a shift in wave climate/refraction patterns, may lead to barrier island fragmentation and a runaway transgression of this predominantly natural barrier island system. Consequently, a grain analysis of major coastal compartments, across multiple driving forces, can be used to assess coastal morphodynamics and the potential impact of climate change on coastal systems.  相似文献   

4.
<正>This study examined spatial variations in the concentration,grain size and heavy mineral assemblages on Cedar Beach(Lake Erie,Canada).Magnetic studies of heavy mineral-enriched,dark-reddish sands present on the beach showed that magnetite(～150μm) is the dominant magnetic mineral.Surficial magnetic susceptibility values defined three zones:a lakeward region close to the water line(Zone 1),the upper swash zone(Zone 2) and the region landwards of the upper swash zone (Zone 3).Zone 2 showed the highest bulk and mass susceptibility(κ,χ) and the highest mass percentage of smaller grain-size(250μm) fractions in the bulk sand sample.Susceptibility(i.e.κandχ) values decreased and grain size coarsened from Zone 2 lakewards(into Zone 1) and landwards (into Zone 3),and correlated with the distribution of the heavy mineral assemblage,most probably reflecting preferential separation of large,less dense particles by waves and currents both along and across the beach.The eroded western section of Cedar Beach showed much higher concentrations of heavy minerals including magnetite,and finer sand grain sizes than the accreting eastern section, suggesting that magnetic techniques could be used as a rapid,cost-effective way of examining erosion along sensitive coastline areas.  相似文献   

5.
A combined field and laboratory study in northern Lake Erie has provided new insights into the origin and dynamics of heavy mineral placer deposits on beaches consisting primarily of non‐magnetic sediment. Work was conducted on the cross‐shore and longshore transport of heavy magnetic minerals using magnetic susceptibility and fluorescent paints to trace the movement, in the field, of samples of magnetic (magnetite) and non‐magnetic (quartz and calcite) grains, respectively. Laboratory experiments examined how the burial of small, dense magnetic minerals is affected by the grain size of the non‐magnetic host material, and how grain burial affects magnetic susceptibility measurements at the surface. The field experiments demonstrated that the magnetic mineral tracers were buried rapidly beneath coarser, non‐magnetic grains under low to moderate wave conditions, and subsequently were unable to move in the longshore or cross‐shore directions. The laboratory experiments showed that the magnetic susceptibility rapidly decreased with the rate and depth of burial of the magnetic minerals, and that magnetic grain burial was most effective beneath coarser rather than finer non‐magnetic sand and, for the latter sediments, under less rather than more energetic conditions. The results imply that magnetic mineral concentrations develop in this area through magnetic grain burial under fairly mild conditions, and subsequent settling, exposure and concentration in the upper swash zone during more energetic periods, when the non‐magnetic grains are eroded. It is probably during these erosional periods, when the magnetic minerals are exposed in fairly homogeneous deposits, that longshore and cross‐shore transport takes place.  相似文献   

6.
河海交互作用沉积与平原地貌发育*   总被引：3，自引：15，他引：3  
河流是搬运陆源泥沙的主要动力,对相邻的海岸海洋沉积动力有巨大影响。中国河流汇入海洋中的泥沙曾占全球入海泥沙的10 ％ ,现代中国边缘海大陆架在晚更新世时曾是海岸平原,河-海交互作用是形成海岸平原与浅海输积泥沙的主要因素。本文选择5个不同类型的河流展示其不同的泥沙运动与河口沉积的特性以及对相邻陆架之影响,包括: 1)强潮型动力的鸭绿江河口湾,形成从陆向海与从海向陆的双向水流交汇沉积,海岸形成潮流脊体系。 2)季风波浪为主导动力的滦河口,以泥沙的横向运动为主,形成沙坝环绕的双重海岸,沉积粒径自海向陆减小; 沿岸浪流携运泥沙向河口两侧分布,使沙坝具有沙咀状的复合特点。 3)弱潮型、多沙的黄河口,径流于两侧堆积指状沙咀,沙咀下风侧形成粉砂粘土淤泥湾,沿岸流携运泥沙向渤海湾延伸为淤泥舌。 4)径流与沿岸流组合作用的沉积模式,以长江口为代表,泥沙沿岸向南输运为主导,向海岸与向内陆架构成颗粒变细的带状沉积,外陆架出露残留砂。 5)充填河口湾的三角洲,以珠江为代表,河流分汊与会潮点泥沙堆积,悬移质扩散至湾外,被沿岸流携带沿海岸向SW运移,外陆架为残留砂沉积。20世纪80年代以来,上述河流均受到人为活动的改造影响,河流自然过程与河海交互作用效应均发生改变。本文主要以滦河三角洲为例阐述河-海交互作用与平原的地貌特征。  相似文献   

7.
为了研究长江口-杭州湾外近海沉积物粒径的现状和近期变化,于2008年4月在该区域用箱式取样器取得了33个表层样,用震动活塞采样器取得7个柱状样;在室内用激光粒度仪对沉积物样品进行了粒度分析并与历史时期的研究成果进行对比。结果表明,1）表层沉积物总体上呈东粗（砂）西细（泥）的特点,粒径总体上的空间格局与历史时期相似;但砂-泥区界线在研究区北部（长江口和杭州湾外）有向西迁移（蚀退）迹象（西移10~30 km）,而在南部（舟山群岛以南）则出现明显向东迁移（淤进）现象（最大超过50 km）。2）当前的表层沉积物形成一条南北连续的泥质带（粒径向南逐渐变细）,反映过去存在于舟山群岛以东的最细组分（“黏土”）带不连续现象在表层现已趋于消失。3）表层沉积物粒径趋势分析揭示长江入海泥沙的运移方向主要是向南-东南。4）泥质区柱状沉积物具有粉砂和黏土为主但在垂向上（反映在时间上）有粗细多变的特点（侵蚀区表层沉积物有粗化迹象）。研究认为,长江口-杭州湾邻近海域现代沉积物对流域和沿海重大人类活动有较敏感的响应。  相似文献   

8.
基于海洋区域地质调查获取的1 438个粒度数据，利用Folk分类方法将中国东部海域表层沉积物划分为砂质粉砂、粉砂质砂、粉砂、砂、砂质泥、泥质砂、泥7种沉积物类型，阐述了不同沉积物类型的粒度组成和参数特征.其中，砂质粉砂、粉砂质砂和粉砂是3种最主要的沉积物类型，分别占样品总数的34.70%、24.20%和15.51%.粉砂质砂呈条带状分布在研究区的南部且向北延伸.粉砂主要分布在长江口-浙闽沿岸、渤海西部和南黄海中北部.砂主要分布在东海外陆架、扬子浅滩和苏北浅滩、朝鲜湾等海区，其中在东海外陆架海区分布最广.影响沉积物分布的主要因素有物源、水动力环境以及水深、地形、地貌等.晚第四纪冰期旋回中海平面变化和海洋环流控制陆源沉积物的入海通量和陆架沉积体系的发育过程.综合沉积物物源供给、海洋环流、冰后期海平面变化过程，基于Folk分类的动力学属性和表层沉积物类型分布，将中国东部海域表层沉积物分布划分为河口沉积、陆架泥质沉积、潮流沉积以及残留沉积等分区.不同沉积分区的形成机制和影响因素差异显著，反映出在中国东部陆架的特殊地形影响下，不同海平面时期陆源碎屑物质的运移过程.   相似文献   

9.
磁铁矿是岩石、土壤和沉积物中少量而又普遍存在的副矿物,是环境磁记录的主要载体.磁铁矿在表生地质过程中受到机械、生物和化学风化作用使其结构、粒径、氧化程度、磁学性质发生一系列变化,这些变化对环境磁学以及表生地质过程的研究具有重要意义.从矿物学角度研究了磁铁矿粒径、相转变、氧化程度和磁化率随着研磨时间的变化规律.结果表明,平均粒径为4 μm的磁铁矿在研磨1 h后粒径变化趋于稳定,但随着研磨时间的增加,磁化率逐步降低而氧化率逐渐增加.通过对研磨后样品进行XRD分析表明,随着研磨时间的增加,磁铁矿衍射峰强度明显减弱,衍射峰宽化,赤铁矿的衍射峰强度逐渐增强.由此可见,原生磁铁矿(对沉积物而言属于碎屑磁铁矿)低温氧化产物是赤铁矿而不是磁赤铁矿.在表生地质演化过程中颗粒的机械碰撞不仅使磁铁矿颗粒变细,而且可能影响到磁铁矿常温氧化、磁学性质和晶体结构.  相似文献   

10.
朱晓东  施丙文 《沉积学报》1997,15(3):145-149
微体古生物的沉积动力分析可提取出比单纯的微体古生物分析更多更准的古沉积环境信息。本文提出一种称为“沉积物粒径指数（ｇｓｉ）”的半定量参数，适用于微体古生物的沉积动力学分析研究。长江口及苏北辐射沙洲区的有孔虫分析实例表明这种沉积物粒径指数行之有效。  相似文献   

11.
福建安海湾表层沉积物粒度特征及其现代沉积过程分析   总被引：1，自引：0，他引：1  
通过对福建安海湾表层沉积物的粒度分析和对比,应用系统聚类分析、粒径趋势模型和切应力计算公式,探讨了研究区粒度的分布特征、沉积环境分区、表层沉积物输运趋势及其影响因素.研究结果表明,研究区包括6种表层沉积物类型,以黏土质粉砂和粉砂为主,沉积物大体呈现自海湾两侧潮滩向潮汐通道变粗的分布趋势.表层沉积物粒度的分布特征与水动力条件和物质来源密切相关,湾口附近及湾内深槽内,细颗粒的沉积物被再悬浮带走,粗颗粒的含量增大;在湾内潮滩上,悬浮物质因水动力作用逐渐减弱发生分选沉降,形成向岸变细的横向分异.海湾外泥沙随潮流不断地向海湾东侧岸滩运移,海湾周边陆源来沙由湾顶部往湾口方向下泄,两者是导致表层沉积物出现明显的顺时针方向汇聚趋势的原因之一;表层沉积物的输运趋势、悬浮泥沙的输运、潮滩植被与湾口沙嘴的遮蔽效应共同影响了研究区内浅滩地形的形成和变化.研究区可分为四类沉积环境区,以潮滩和潮汐通道环境为主,不同沉积区内的粒度参数、粒级频率和敏感粒级均有差异,动力条件差异和不同物源的影响程度是现代沉积环境格局的主要影响因素.  相似文献   

12.
应用部分非磁滞剩磁(pARM)谱,对山西宁武天池干海湖泊沉积物携带的磁信息研究表明,粗磁铁矿颗粒(MD)是主要载磁矿物颗粒,其pARM谱在低矫顽力区间(AF20 mT)达到最高值;而细磁铁矿颗粒(PSD-SD)为次要载磁颗粒,其pARM谱在高矫顽力区间(AF20 mT)稍有突起。但是,剖面三个层位具有不同特征,上层(大约7.3~4.0 ka)的粗磁性矿物颗粒含量最高,下层(大约12.0~13.0 ka)次之,而中层(大约12.0~7.3 ka)相对最低;中层的细磁性颗粒含量最高,下层和上层的细磁性颗粒含量次之。pARM谱分析结果与磁滞曲线测量获得的磁畴结果一致。在较高的交变磁场区间获得的pARM可以有效地压抑粗磁颗粒的信息,进而使细磁颗粒的信号增强。应用pARM谱分析,能有效判别样品中磁性矿物的磁畴状态,有助于沉积物的古气候、岩石磁学和古地磁学研究。  相似文献   

13.
It is widely recognized that lake sediment grain‐size distributions tend to be polymodal and consist of two or more grain‐size components. However, for specific cases, the genesis of each component usually is poorly understood. In this study, the grain‐size components of the surface sediments of Hulun Lake, Inner Mongolia, were partitioned using the log‐normal distribution function method and the relationship between the identity of each grain‐size component and the hydraulic condition of the lake was investigated in order to relate the constituent components to specific depositional processes in the lake. The data indicate that the modern clastic sediments of Hulun Lake contain six distinct unimodal grain‐size distributions representing six grain‐size components. Each of the components retains its identity including modal size, manner of transportation and environment of deposition, although the relative percentage varies with the hydraulic conditions throughout the lake. These components are specified from fine to coarse modes as long‐term suspension clay, offshore‐suspension fine silt and medium to coarse silt, and nearshore‐suspension fine sand, saltation medium sand and traction coarse sand. The percentage contribution of several grain‐size components interpreted as being indicative of nearshore environments is shown to be correlated negatively with water depth across the modern lake bed; this suggests that the proportion of these components in core data might be useful as a proxy for water depth. This possibility was tested using a sediment core from Hulun Lake where high percentages of the nearshore grain‐size components were found to be correlated with low regional precipitation reconstructed from the pollen profile of the same core. The coincidence of two independent proxies does not only demonstrate the validity of log‐normal distribution function in partitioning polymodal sediments but reveals the potential of lake sediment grain‐size components for the research of lake‐level fluctuations during the geological past.  相似文献   

14.
长江口附近的沿岸流和水团变化对研究长江三角洲沉积物的“源-汇”机制具有重要意义.对HZK2孔沉积物的粒度、年龄和有孔虫分布特征进行了研究分析.结果表明:HZK2孔52.5 m以上有孔虫均有分布，底栖有孔虫丰度在12 m以上和26.0~52.5 m含量超过40枚/g，代表不同沿岸流和水团的有孔虫属种含量在垂向上呈现明显的分带性.HZK2孔全新世以来经历了河口湾和水下三角洲两大沉积体系，并在全新世早期发育潮流沙脊.末次冰消期，钻孔所在位置受长江冲淡水和苏北沿岸流共同影响.全新世早期，则受苏北沿岸流影响为主；在此之后，长江口冲淡水的作用减弱，苏北、黄海沿岸流影响较强.全新世中晚期，苏北沿岸流、长江冲淡水、江浙沿岸流和东海外海水团多种水体共同作用钻孔所在海域，全新世晚期长江冲淡水作用占绝对优势.   相似文献   

15.
Both sediment recycling and first-cycle input influence the composition of clastic material in sedimentary systems. This paper examines conceptually the roles played by these processes in governing the composition of clastic sediment on a regional scale by outlining the expected effects on sediment composition of protracted sediment recycling and of continuous first-cycle input on a maturing continental block. Generally speaking, long-term recycling tends to enrich sediments in the most chemically and mechanically stable components: quartz in the sand and silt size fractions, and illite among the clay minerals. Sandstones trend towards pure quartz arenites, and mudrocks become more potassic and aluminous. The average grain size of clastic sediment decreases by a combination of progressive attrition of sand grains and ongoing breakdown of primary silicate minerals to finer-grained clay minerals and oxides. Sandstones derived by continuous first-cycle input from an evolving continental crustal source also become increasingly rich in quartz, but in addition become more feldspathic as the proportion of granitic material in the upper continental crust increases during crustal stabilization. Associated mudrocks also become richer in potassium and aluminum, but will have higher K2O/Al2O3 ratios than recycled muds. The average grain size of the sediment may increase with time as the proportion of sand-prone granitic source rocks increases at the expense of more mud-prone volcanic sources. In general, except in instances where chemical weathering is extreme, first-cycle sediments lack the compositional maturity of recycled detritus, and are characterized by the presence of a variety of primary silicate minerals. Sedimentary systems are not usually completely dominated by either recycling or first-cycle detritus. Generally, however, sedimentary systems associated with the earliest phases of formation and accretion of continental crust are characterized by first-cycle input from igneous and metamorphic rocks, whereas those associated with more mature cratons tend to be dominated by recycled sedimentary material.  相似文献   

16.
As the largest industrial city locating in the Northwestern China, Lanzhou has become one of the most seriously polluted cities in the world. In this study, investigations were performed on the magnetic properties, heavy metals and organic matter contents of a total of 23 sediment samples collected from eight selected rivers in the Lanzhou urban area. The results of the study indicate that the magnetic properties of the sediment samples are predominated by low-coercivity magnetite. The river sediments are classified into three types, i.e., downstream polluted, upstream polluted, and less affected, based on the contribution from anthropogenic activities in different segments of the river as indicated by the variation of magnetic mineral concentration parameters. Moreover, a strong linear positive correlation exists among some of the magnetic parameters and organic matter content, heavy metals (Cr, Ni, Pb, Zn, Fe) and total enrichment factor (R) of the bulk deposit samples, which indicates that environmental magnetic technology may be an effective method for distinguishing source apportionment and monitoring river sediment pollution in urban areas.  相似文献   

17.
渤海湾西部表层沉积物粒度特征与沉积混合   总被引：2，自引：0，他引：2  
田立柱  耿岩  裴艳东 《地质通报》2010,29(5):668-674
根据渤海湾西部135个表层沉积物样品的粒度分析结果,分析了表层沉积物的粒度特征与规律。整体上由研究区东北部沿海岸向南沉积物粒度变细,由砂和粉砂质砂变为砂质粉砂,再变为粘土质粉砂。沉积物粒度频率曲线显示,由研究区东北部至北部,沉积物粗组分含量减少,由单峰逐渐过渡为主峰或弱峰,到中部粗组分减少为粗尾形态,到南部粗组分几乎缺失;而沉积物细组分的变化趋势则与之相反。沉积物粗组分在粒度频率曲线上的表现由单峰逐渐过渡至主峰或次峰,粗峰含量减少,到中部粗组分减少为粗尾形态,到南部粗组分几乎消失;而沉积物细组分的变化趋势则与之相反。沉积物粒度参数的平面分布规律和粒度参数之间的相关性变化形态显示出粗细2种母质组分以不同比例的沉积混合的特征,即来自东北部的粗组分与来自南部的细组分发生混合,这可能主要与区内双向的沿岸环流输运有关。  相似文献   

18.
亚洲内陆晚新生代干旱化历史及其驱动机制是非常重要的科学问题。选择天山北麓柴窝堡盆地南缘乌鲁木齐河剖面为研究对象,基于磁性地层年代学研究建立的时间标尺,分析了该剖面碎屑沉积物岩石磁学特征及其控制因素,进一步探讨了柴窝堡盆地晚新生代古气候特征。磁性地层年代学研究约束乌鲁木齐河剖面底界年龄为~6.8 Ma,顶界年龄为~3.3 Ma。详细的岩石磁学测量及漫反射光谱分析结果表明,乌鲁木齐河剖面沉积物中磁性矿物主要包括磁铁矿、赤铁矿等,磁学参数χlf、χARM、SIRM、S-100mT、S-300mT、 χARM/SIRM等在~6.3 Ma、~5.2 Ma存在明显变化,揭示磁性矿物粒度、含量等存在相应变化,如在~6.3 Ma前后,磁性矿物颗粒逐渐变粗、含量降低;在~5.2 Ma前后,磁性矿物颗粒逐渐变细后趋于稳定、含量逐渐增多。基于稀土元素分析、沉积粒度与磁学参数相关性分析,认为沉积物源与沉积物粒度不是导致乌鲁木齐河剖面磁学性质变化的主要因素,自~6.8 Ma以来逐步干旱化的气候条件可能是导致该剖面磁学特征变化的重要原因。基于漫反射光谱分析得到的红度与亮度数据结果也揭示了同样的古气候特征。  相似文献   

19.
张丹  王张华  卫巍  李晓 《第四纪研究》2009,29(2):308-317
对长江三角洲地区7个晚新生代钻孔沉积物的岩石地层和磁化率特征进行详细对比,并进一步选择浦东机场孔（PD孔）进行了详细的岩石磁学测试,讨论了该地区的晚新生代沉积物物源的演变。结果显示沉积物磁性的4次显著变化：  1）各钻孔上新世磁性强弱差异明显;   2）早更新世早期本区普遍表现出弱磁性;   3）从早更新世中晚期至全新世,磁性强度一般随粒度粗细变化波动,即砂质沉积磁性强,泥质沉积磁性弱;   4）晚更新世晚期以来,细颗粒沉积物的磁性较明显增强。磁性参数分析显示上新世和早更新世早期磁性矿物晶体颗粒较细,早更新世中晚期-晚更新世以粗晶粒磁性矿物为主,全新世细晶粒磁铁矿再次占主导。我们认为上述磁性变化反映构造沉降控制下现代长江三角洲地区物源区的不断扩大。  相似文献   

20.
 Geochemical characteristics of six trace metals – Cu, Co, Ni, Zn, Cd and Cr – in the bulk sediment and sand, silt and clay fractions of a tropical estuary on the southwest coast of India have been studied and discussed. In bulk sediment, the trace metal concentration is controlled mainly by the textural composition of the sample. Mud, sandy mud and sandy silt register higher concentrations of trace metals than that in sand-dominant sediments. The granulometric partitioning studies also re-affirmed the role of particle size in enriching the trace metals. The silt and clay fractions exhibit 7–8 times the enrichment of Cu and Cd compared to that in sand. The enrichment factors of Zn, Cr, Ni and Co in the silt and clay fractions, compared to that in sand, are 5–6, 4–5, 2–5 and 2–3 times, respectively. The trace metals in the sand fraction, particularly Ni and Cr, exhibit strong positive correlation with the heavy mineral content of the samples. It clearly indicates a heavy mineral pathway to the trace metals in the sand fraction. Cu and Co in silt and clay fractions exhibit a marked decrease towards the high saline zones of the estuary. This is attributed to the desorption of Cu and Co from particulate phases during estuarine mixing. Contrary to Cu and Co, the content of Zn in the clay fraction shows a marginal increase towards the estuarine mouth. This could be explained by the influx of Zn-rich contaminant discharges from Zn-smelting industries located slightly north of the estuarine mouth. The released Zn will effectively be held in the lattices of the clay mineral montmorillonite, which also exhibits a marked increase towards the estuarine mouth. The anomalously high values of Cd in some places of the Central Vembanad estuary is attributed to the local pollution. Received: 10 July 1995 · Accepted: 3 June 1996  相似文献   

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