内湾沉积物生物硅化学测定法的实验条件探讨

对国内外已经建立的几种生物硅的测定方法进行简要的评述,并详细地对内湾沉积物中生物硅化学提取法的条件选取进行实验探讨,对低生物硅含量的内湾沉积物测定提出了较优的条件。     

Textural characteristics and morphosedimentary environment of foreshore zone along Ganpatipule,Maharashtra, India

The cross-shore profile and the textural distribution of foreshore sediments of Ganpatipule beach along Maharashtra coast covering two annual cycles are examined. Ganpatipule beach depicts erosion and accretion of the berm, reduction and widening of foreshore widths during the monsoon (June–September) and post-monsoon (October–May), respectively with net sediment accretion during the study period due to the changes in the wave characteristics. A direct correlation is observed between the median sediment grain size and beach-face slopes signifying high wave energy ensuing to a gentle to very gentle slope. The sediments are mainly medium grain size, moderately well sorted, bimodal, very fine skewed to very coarse skewed and very platykurtic to very leptokurtic in nature. The binary plots of the textural parameters (mean, skewness, kurtosis, and standard deviation) depicted a characteristic beach environment of deposition. The study shows that the sediment is concentrated in the environment of rolling and bottom suspension. The study on grain size distribution of sediments could be used to assess the wave energy condition prevailing along the coastal area.     

渤海湾西部表层沉积物悬移组分元素特征及物源意义

对渤海湾西部海底表层沉积物样品粒径小于0.063mm的悬移组分进行16种元素测试,分析了各元素特征及分布规律。元素平均丰度与黄土及渤海泥质沉积物基本一致,说明渤海湾西部表层沉积物悬移组分的物源主要与黄河源区黄土高原的黄土有关。研究区16种元素可分为两类,I类是Sc、Co、Fe、V、Al、Ca、Mg、Th、U、Cr;II类是Zr、Hf、Ba、Na、Sr、K。同类元素丰度的平面分布规律相似,呈现正相关性;异类元素丰度的平面分布规律相反且呈负相关性。研究区主要分为两个地球化学分区,两区基本以北纬39°05′线为界,I区位于南部和中部,以高Sc、Co、V、Th、U、Cr、Fe、Al、Mg、Ca等I类元素为特征;而II区位于北部,以高Zr、Hf、Ba、Sr、Na、K等II类元素为特征。渤海湾西部表层沉积物悬移组分的元素特征及分区,可能与研究区内不同季节沿岸环流方向改变,进而导致不同物源母质沉积物输运混合作用有关。     

Smectite formation in metalliferous sediments near the East Pacific Rise at 13°N

A 43 cm long E271 sediment core collected near the East Pacific Rise(EPR) at 13°N were studied to investigate the origin of smectite for understanding better the geochemical behavior of hydrothermal material after deposition.E271 sediments are typical metalliferous sediments. After removal of organic matter, carbonate, biogenic opal,and Fe-Mn oxide by a series of chemical procedures, clay minerals(2 μm) were investigated by X-ray diffraction,chemical analysis and Si isotope analysis. Due to the influence of seafloor hydrothermal activity and close to continent, the sources of clay minerals are complex. Illite, chlorite and kaolinite are suggested to be transported from either North or Central America by rivers or winds, but smectite is authigenic. It is enriched in iron, and its contents are highest in clay minerals. Data show that smectite is most likely formed by the reaction of hydrothermal Fe-oxyhydroxide with silica and seawater in metalliferous sediments. The Si that participates in this reaction may be derived from siliceous microfossils(diatoms or radiolarians), hydrothermal fluids, or detrital mineral phases. And their δ30 Si values are higher than those of authigenic smectites, which implies that a Si isotope fractionation occurs during the formation because of the selective absorption of light Si isotopes onto Feoxyhydroxides. Sm/Fe mass ratios(a proxy for overall REE/Fe ratio) in E271 clay minerals are lower than those in metalliferous sediments, as well as distal hydrothermal plume particles and terrigenous clay minerals. This result suggests that some REE are lost during the smectite formation, perhaps because their large ionic radii of REE scavenged by Fe-oxyhydroxides preclude substitution in either tetrahedral or octahedral lattice sites of this mineral structure, which decreases the value of metalliferous sediments as a potential resource for REE.     

北太平洋赤道海域表层沉积物的热释光特征及其指示意义

热释光是矿物晶体接受环境核辐射作用后积蓄起来的能量在受到热激发时以光的形式释放出来的一种物理现象,它与晶体损伤、晶体中杂质混入等原因所导致的晶格缺陷有关.热释光强度的大小主要取决于自然界中长寿命放射性元素(238U,235U,230Th,40K及其子体)的衰变,与其他物理、化学、生物或人类活动无关.热释光特征能有效反映晶体形成的环境条件.热释光方法的制样简单、测量快捷,因此在辐射学、核工业、核医学、环境学、农业、考古学、地质学等领域都得到了广泛的应用.在陆地地质学上热释光方法在地质年代测定[1,2]、地层对比[3]、矿物世代划分[4]、矿床含矿评价[4,5]、陨石形成热的历史恢复[6]以及地质事件识别[7]等方面都取得了不少成果.     

海水盐度对沉降泥沙固结过程影响研究

黄河每年输送上亿吨泥沙入海,其中80%以上沉积在河口附近水下三角洲。受黄河入海径流量、气候及海洋动力条件影响,黄河口海域海水盐度变化显著。目前,不同盐度海水环境下入海泥沙沉降形成的海床土,固结过程有何差异尚不清楚。本文在黄河水下三角洲潮坪配制不同盐度的流态沉积物,模拟不同沉积环境下新沉积土的固结过程,利用轻型贯入测试、十字板剪切测试等现场原位试验,实时观测沉积环境盐度对沉降泥沙固结过程的影响。研究发现:随着海水盐度增加,沉积物固结强度增大,沉积环境盐度每增高1‰,沉积物固结后强度可增加0.15倍;海水盐度对沉积物固结速率的影响,在初始阶段表现不明显,在沉积物固结后期,盐度每增高1‰,固结速率可增长1.23倍;海水盐度的增高,还加剧了沉积物固结强度的空间非均匀性。本研究的发现,促进了对河口区海底工程环境的认识。     

Patterns and controls of surface sediment distribution: west-central Florida inner shelf

The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems.     

衡水湖湿地底泥重金属污染及潜在生态风险评价

测定了衡水湖湿地20个采样点底泥中的7种重金属含量,并与环境背景值进行了比较。结果显示,衡水湖湿地底泥中的Hg含量普遍高于环境背景值,为衡水湖湿地底泥中主要富集的重金属元素,而Cr和Cd基本无富集。用地积累指数、某种重金属的潜在生态危害系数和多种重金属的潜在生态风险指数评价了各个采样点的污染程度和潜在生态风险。结果表明,Hg为高风险元素,底泥中重金属污染主要以Hg为主;衡水湖湖内大部分地区的潜在生态风险相对较低,综合潜在生态风险最高处为魏屯闸,然后依次为南关闸、106国道、大赵闸和湖内岛,核心区的综合潜在生态风险最小。另外,还对魏屯闸处的3个采样点的多种重金属的潜在生态风险指数值进行了讨论。     

沉积物粒度对水合物形成的制约：来自IODP 311航次证据

对取自IODP 311航次（东北太平洋Cascadia大陆边缘）所有5个站位、采样间距约为1.5 m的614件沉积物样品，利用Beckman Coulter LS 230激光粒度仪进行了沉积物粒度分析，获得了沉积物粒度随深度变化特征，进而与水合物层位的替代指标进行了位置对比，这些指标包括特殊沉积构造（soupy和mousse like构造）、测井数据（LWD）推算出来的水合物饱和度（Sh）、岩芯红外图像和实际钻取的含水合物沉积物等。发现沉积物粒度分别为31~63 μm和63~125 μm的2组较粗粒径的沉积物数量变化增多的位置与水合物出现层位之间存在较好的位置对应关系。如在U1326站位海底以下5~8 m、21~26 m、50~123 m、132~140 m、167~180 m、195~206 m、220~240 m深度位置出现了沉积物粒度明显偏向粗粒的趋势，而这些位置正好对应于大多数特殊沉积构造出现的深度，也对应于水合物饱和度（Sh）值相对较高的深度，并与一些实际钻取的赋含水合物的浊积沙层观察结果一致。因此，初步研究后认为，沉积物粒度在水合物形成过程中扮演了重要角色，天然气水合物可能偏向形成于粒度大于31 μm的粗粒沉积物中。       

Geoacoustic Characterisation of Fine-grained Sediments using Single and Multiple Reflection Data

Fine-grained sediments commonly occur in areas of the continental shelf where wave and current energy are weak. Bulk density, compressional wave speed and attenuation are fundamental physical properties of these sediments required for predicting the response of the seabed for diverse branches of marine science. The traditional coring approach is time and labor-intensive, with large uncertainties associated with sediment disturbance in the sampling phase. Acoustic methods offer the advantages of remote sensing, i.e., sampling the sediment structure without mechanical disturbance and a significantly larger seabed coverage rate per unit time. Two different acoustic methods are described: one using short-range single-bounce interactions with the seabed, and the second using long-range modal propagation to infer the sediment properties. The relative strengths and sensitivities of each approach are explored through simulations guided by experience with measured data.