Surface textures of turbidite sand grains, Laurentian Fan and Sohm Abyssal Plain

Surface textures of quartz grains have been examined from five samples from the Laurentian Fan and Sohm Abyssal Plain, representing varied transport distances and power of the depositing turbidity current. The grains retain their primary irregular shape derived from glacial erosion, and glacial surface textures are preserved in dish-shaped depressions. These features have been superimposed by a slight rounding of edges and an abundance of collision-induced markings, particularly mechanical V-forms. The most intense current modification of this sort occurs in mid-Wisconsinan or earlier sands that have been transported over 1000 km to the distal Sohm Abyssal Plain by turbidity currents. Collision textures probably develop during grain flow on the steep continental slope: delicate resedimented shelf foraminifera are preserved in the same turbidites and most have been transported exclusively in suspension.     

Micromanganese nodules in deep-sea sediments: Uranium-isotopic evidence for post-depositional origin

Micromanganese nodules from three deep-sea cores are found to contain less U than average nodules dredged from the sea floor. The ${}^{234}\text{U}{}^{238}\text{U}$ ratio in these micronodules is higher than any previously reported in deep-sea sediments. We interpret these data to mean that at least some micronodules form well after deposition of the enclosing sediments, in particular where conditions are less oxidizing than average.     

Dating fault activity by surface textures of quartz grains from fault gouges

Surface textures of quartz grains from fault gouges are examined by means of the scanning electron microscope. It is disclosed that the surface morphology of the grains is variable, but quartz grains extracted from one fault gouge sample commonly show a type of texture different from those observed on the grains from the other samples. The surface textures observed under the microscope are tentatively classified into eight types; subconchoidal, orange peel-like, fish scale-like, moss-like, moth-eaten, stalactitic, pot-hole, and coral-like textures. These textures can be classified into four groups. Arranged in the order of their apparent features, it is interpreted that the progressive corrosion of quartz grains by ground water has taken place after faulting. The change of this surface feature can assist in estimating the time elapsed since the last fault activity.     

A scanning electron microscope study of surface textures of quartz grains from glacial environments

Surface textures of quartz sand grains from several glacial environments at the Feegletscher, Switzerland examined by means of scanning electron microscopy are described. The difference between supraglacial and subglacial material is very slight. At the moment the interpretation of these textures must be done with care until the full statistical relation to environments can be ascertained. This does not necessarily invalidate earlier investigations although it does mean that glacial and extraglacial environments in the vicinity of glaciers are apparently not distinguishable. Examination of surface precipitation features suggests a sequence of events which can be used to help discriminate between different ages of deposits in an area. A similarity between some of the surface debris from moraine samples and those seen in loess and quickclay deposits is also suggested.     

Iodine diagenesis in non-pelagic deep-sea sediments

Measurements of sediment geochemistry and porewater speciation have been made using eight cores containing turbidite sections from the Madeira and Nares Abyssal Plains. The results have been used to evaluate how the diagenetic chemistry of iodine in these sediments compares with that in sediments undergoing steady-state diagenesis. The behaviour of iodine is related to the development of a redox front within the turbidite, between the organic-rich anoxic sediment and its oxic cap, and the downward migration of the front through the turbidite with time. In contrast to the steady-state case, sediment I contents and I/ C ratios increase downwards through the oxidised section reaching a maximum at the redox front (up to ~ 100 μ/g I; molar I/C~ 20 × 10⁻⁴) below which values drop dramatically (I/C ~ 5 × 10⁻⁴). A strong iodate enrichment (up to ~3 μmol kg⁻¹) is observed in the oxidised section of the sediment. At the front interconversion of I⁻ and IO⁻₃ species occur and below the front porewater IO⁻₃ is absent and I~ concentrations increase with depth (as in other cases of anoxic diagenesis) up to ~ 10 μmol kg⁻. In the oxidised section of the sediment the I enrichment has been supplied by upward transport of iodide with the increasing I content, with depth being accounted for by progressive diagenetic enrichment with time.     

An application of scanning electron microscopy of quartz sand surface textures to the environmental diagnosis of Neogene carbonate sediments, Finestrat Basin, south-east Spain

The Finestrat Basin, 25 km NE of Alicante, contains a poorly understood sequence of Neogene sediments that lack an indigenous fauna. Study of the surface textures of euhedral quartz grains, probably derived by first-cycle weathering from an underlying Triassic mudstone diapir, provides new data on the depositional environment of the basin. The possible influence of alluvial fans is recorded by mechanical breakage features in these non-glaciated sediments. The distribution and abundance of chemical etch pits suggest their diagenetic origin following non-marine deposition, while the density and abundance of mechanically induced ‘V’-shaped pits seems typical of fluvial and low-energy littoral environments. The presence of silica precipitated during transport, such as silica globules, suggests a silica-rich transport medium and a depositional environment that was not highly alkaline. In combination with independent sedimentological evidence, these data suggest that the sediments collected in a lake after derivation by rivers and alluvial fans from the diapir. It is concluded that the abundance and superposition of features must be noted for each grain in order to yield useful results, and that the mechanisms acting on each grain be deduced before attempting to identify specific environments.     

Hindered settling of sand grains

The sedimentation rate of sand grains in the hindered settling regime has been considered to assess particle shape effects. The behaviour of various particulate systems involving sand has been compared with the widely used Richardson–Zaki expression. The general form of the expression is found to hold, in as much as remaining as a suitable means to describe the hindered settling of irregular particles. The sedimentation exponent n in the Richardson–Zaki expression is found to be significantly larger for natural sand grains than for regular particles. The hindered settling effect is therefore greater, leading to lower concentration gradients than expected. The effect becomes more pronounced with increasing particle irregularity. At concentrations around 0·4, the hindered settling velocity of fine and medium natural sands reduces to about 70% of the value predicted using existing empirical expressions for n. Using appropriate expressions for the fluidization velocity and the clear water settling velocity, a simple method is discussed to evaluate the sedimentation exponent and to determine the hindered settling effect for sands of various shapes.     

Iodine diagenesis in pelagic deep-sea sediments

Nineteen sediment cores from the Madeira, Seine, Tagus and Nares Abyssal Plains and the Alboran Sea have been used to evaluate the speciation, fluxes and diagenesis of iodine in the deep sea. The sediments have surficial molar I/C ratios of 10–30 × 10⁻⁴ in excess of previous reported values for planktonic material (~1 × 10⁻⁴). Solid phase I contents decrease exponentially with depth corresponding to decomposition rate constants of 5–260 × 10⁻⁶ yr⁻¹ which vary with the carbon accumulation rate.Iodine species in the pore waters follow a vertical sequence of four zones: 1. a zone of I⁻ production where total dissolved iodine (∑I) concentrations initially increase at the seawater-sediment interface; 2. a zone of I⁻ oxidation where interconversion of I⁻ to IO⁻₃ occurs; 3. a zone of IO⁻₃ reduction where interconversion of IO⁻₃ back to I⁻ occurs which corresponds to the suboxic part of the sediment column; and 4. a further zone of I⁻ production which is confined to the lower anoxic part of the sediment column. Benthic ∑I fluxes in the Madeira Abyssal Plain measured from shipboard incubation experiments and calculated from porewater gradients are similar, averaging 0.55 and 0.36 × 10⁻⁸ μmol cm⁻² sec⁻, respectively.In the surface sediment the observed I enrichment results from a quasi-closed cycle for iodine initially involving release of I⁻ from decomposing marine organic matter followed by rapid removal onto organic matter at the sediment-seawater interface where I/C regeneration ratios of up to 200 × 10⁻⁴ are found, lodate reduction occurs during suboxic diagenesis, after denitrification and before MnO₂ reduction, consistent with the sequence of reactions predicted from the free energy yields for organic matter oxidation. There is some further I⁻ production in the anoxic section of sediments but at much smaller rates than occur during the interfacial diagenetic cycling.     

Fatigue effects in quartz sand grains

Particles of quartz sand from a stream draining granite were found to exhibit noteworthy effects of fatigue. Both repeated static loading and collective movement in water weakened the particles markedly. This weakening must have significance in nature, where repeated stressing occurs in many environments, particularly in soils and during bed-load motion in both air and water. Tectonic movements may also create fatigue effects in sand grains. Fatigue effects appear also to be sufficiently pronounced to be significant in some industrial processes involving the use of sand.     

Fracturing mode analysis and relative age dating of faults by surface textures of quartz grains from fault gouges

Surface textures of quartz grains taken from about 250 samples of fault gouges in faults ranging in length from several metres to several tens of metres with the faults extending several tens to several hundreds of kilometres in length, are examined by means of the scanning electron microscope and are categorized into four groups from I to IV, based on the smoothness of the surface, degree of undulation and development of cavities, as mentioned in a previous paper. Based on surface features of quartz grains from faults the geological age of movement of which is known, the groups I to IV are tentatively related to the age of formation of quartz grains and the period of formation of surface textures. This correlation makes it clear that quartz-grain surface textures are an important clue to dating a relative age of faulting. River patterns, striations, granular fracture surfaces, and dimple-like textures are observed to appear on less corroded surfaces of quartz grains from fault gouges. Fractographic analysis of these surfaces of quartz grains should be a clue to revealing the mode of fracture of the fault movement which released the quartz grains into the fault gouge.     

Uranium in pacific deep-sea sediments and manganese nodules

A total of 1344 manganese nodules and 187 pelagic sediments from 9 areas in the North and the South Pacific were analyzed for U by the delayed-neutron counting technique. A strong positive correlation between U and Fe in nodules and sediments suggests a co-precipitative removal from sea water into the Fe-rich ferromanganese mineral phase δ -MnO₂. Enrichment of U and Fe in nodules from the northwestern slopes of two submarine hills (U between 6 and 9 ppm) in the equatorial nodule belt is thought to be caused by directional bottom water flow creating elevated oxygenized conditions in areas opposed to the flow. Economically important nodule deposits from the nodule belt and the Peru Basin have generally low U contents, between 3 and 5 ppm. Insignificant resources of U of about 4 × 10⁵ in the Pacific manganese nodules are estimated.     

The origin of framboidal pyrite as a surface effect of sulphur grains

Framboidal pyrite has been prepared by precipitation of oxyhydroxides of iron, peptized by humic acids using a solution of Na-sulphate or hydrogen sulphide, spherical grains of elemental sulphur being present. By peptization of iron oxyhydroxides using humic acids, a stable negatively charged colloidal system arises. At room temperature and a pressure of 1 atm., and at pH widely ranging between 6.5–7.5, sulphidation of this colloidal system gives rise to a monodispersive sulphidic sol whose stability depends on the concentration of iron in the solution, the amount of humic acids and the presence of electrolytes. In the presence of spherical grains of sulphur, arising by rapid oxidation (acidification) of Na₂S solution or a saturated solution of hydrogen sulphide, particles of the sulphidic sol precipitate on their surface and the grains become gradually replaced by sulphides of iron. At the same time, framboids of an average diameter of 14 μm are generated.     

Diffusion of ions in sea water and in deep-sea sediments

The tracer-diffusion coefficient of ions in water, D_j⁰, and in sea water, $\text{D}{}_{\mathrm{j}}{}^1$, differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective $\text{D}{}_{\mathrm{j}}{}^1$ or D_j⁰ values. The tracer diffusion coefficients of ions in deep-sea sediments, D_j,sed., can be related to $\text{D}{}_{\mathrm{j}}{}^1$ by $\text{D}{}_{\mathrm{j,sed.}}\text{= D}{}_{\mathrm{j}}{}^1\text{·}\text{α}\text{θ}{}^2$, where θ is the tortuosity of the bulk sediment and a a constant close to one.     

Sub—microscopic Textures and Retrogressive Metamorphic Origin of Longxi Nephrite

Nephrite specimens from Longxi,sichuan,prepared by ion-thinning and dispersion techniques have been studied using TEM and SAED.A series of sub-microscopic textures such as (010)multiple-chain faults and related fault terminations.(001)mechanical twinning,sub-grain boundaries or fault walls,tremolite fibrous pseudoform of talc and intergrowth of tremolite and talc with (010)as interface are revealed .By analogy of metallographic textures,characteristics and mechanisms of the process of “deformation-recovery-recrystallization“ are discussed in detail,Topotactic reaction mechanism by which tremolite retrogresses to talc was studied and a retrogressive metamorphic origin of Longxi nephrite is proposed.     

四川盆地白垩纪沙漠石英沙颗粒表面特征

石英具有较大的硬度和较高的化学稳定性，因而其颗粒表面特征能很好地反映沉积环境。而通过扫描电镜研究石英颗粒表面微细特征是分析沉积环境行之有效的方法。虽然多数人认为四川盆地白垩纪地层存在沙漠沉积(打儿凼组和夹关组)，但仍有人对沙漠沉积的存在持怀疑态度，并认为是河流成三角洲沉积。过去关于其沉积环境的判别主要是根据沉积结构和构造，并未对其石英沙颗粒表面特征进行过系统分析。笔者对采自四川盆地白垩系不同层位地层的样品进行了石英沙颗粒表面特征系统分析。结果表明，石英沙颗粒表面特征分析可以成功地将石英沙区分为风成和水成沉积。因此，本文从石英沙颗粒表面特征方面进一步肯定了四川盆地白垩纪古沙漠的存在。     

26Al-10Be systematics in deep-sea sediments

We report the development of a NaOH-leaching technique to extract the authigenic Al and Be in marine sediments, which should allow the sedimentary signals of cosmogenic ²⁶Al and ¹⁰Be to be more effectively studied as geochemical/geophysical tracers. The technique has been applied to the study of ²⁶Al and ¹⁰Be in opal-rich sediments from the North Pacific. The ²⁶Al/²⁷Al and ¹⁰Be/⁹Be ratios of ~3 × 10⁻¹⁴ and 1 × 10⁻⁷ leached from the sediments are higher than those in the total sediments by factors of 3–10 and 2–3, respectively. The authigenic ¹⁰Be/⁹Be ratios are similar to those in deep waters at the study site, pointing to the potential usefulness of the ratios in paleoceanographic studies. The fractions of total Be and Al in the sediment studied that are of authigenic origin average about 40 and 17%, respectively. Estimated ²⁶AL/²⁷A1 ratios in detrital sediments are ≤ 10⁻¹⁵, low enough to indicate that the source of ²⁶Al in the ocean mainly comes from atmospheric production. In the study area, the deposition flux of ²⁶Al is comparable to its atmospheric supply. However, the deposition flux of ¹⁰Be is about threefold higher than the atmospheric input, signifying lateral transport of ¹⁰Be from the open ocean to this area of relatively high particle flux. The ²⁶Al/¹⁰Be ratio, being insensitive to the oceanic influx of lithogenic particles, may serve as a valuable proxy for paleoproductivity. Both the authigenic and total-sediment ²⁶Al/²⁷Al and ¹⁰Be/ ⁹Be ratios decreased significantly at ~6 ka, which could reflect an enhanced input of windblown lithogenic particles to the North Pacific. While the enhanced dust input did not significantly alter the deep-water ⁹Be concentration, it contributed to the observed increase of authigenic ⁹Be flux to the sediment.     

风成沉积物中不同粒径石英颗粒表面机械结构的变化特征

按搬运方式将风成石英颗粒分级,逐级测量并统计表面机械结构的类型、数量和大小,并计算其面积。发现悬移为主的颗粒表面结构的类型、数量最少,仅见少量不规则坑、V形坑,在颗粒表面分布面积最小;跃移搬运为主的颗粒表面结构类型最丰富,不规则坑、蝶形坑、V形坑、新月形坑、贝壳状断口大而深,在颗粒表面的分布面积最大;滚动搬运为主的颗粒表面结构数量最多,以小而浅的不规则坑为主,伴有Ⅴ形坑、贝壳状断口等,在颗粒表面的分布面积大小适中。不同搬运方式在石英颗粒表面形成的结构不同,撞击频率、颗粒大小、搬运速度共同影响表面结构的发育,高撞击频率、大粒径可以形成并承载更多的表面结构,大动能撞击可形成多种类且大尺寸的表面结构。在借助石英颗粒表面结构进行成因判别时需根据粒径大小选择相应粒级的石英颗粒表面结构特征组合,以及结构的数量、大小特征等进行综合判别。     

深海沉积物中的稀土矿产资源研究进展

近年发现,太平洋和印度洋的深海盆地中存在大量富含稀土的深海沉积物。主要类型为多金属软泥、沸石黏土和远洋黏土,其中的全稀土含量(∑REY,∑REE+Y)为400×10-6~2000×10-6,最高可达6600×10-6,重稀土含量(HREE)已达到或超过中国南方离子吸附型矿床的重稀土品位两倍以上,是潜在的新型稀土资源,具有重要的经济价值。目前不少学者对富稀土的深海沉积物进行了大量地球化学及部分矿物学的工作,认为多金属软泥中的稀土元素多赋存于与海底热液作用有关的铁锰氧化物和氢氧化物中,而沸石黏土和远洋黏土中稀土元素的富集则与磷酸盐的混入密切相关,其稀土元素主要存在于与磷灰石成分相当的生物鱼骨屑中。深海黏土的北美页岩标准化稀土配分模式与海水相似,表明其中的稀土元素主要来自于海水,REY富集成矿可能主要受控于磷灰石早期成岩阶段,期间稀土元素未发生分异。尽管近些年对深海沉积物中的稀土元素研究取得了不少成果,但是,对于沉积物中的稀土富集机制及影响因素等问题仍然需要更加深入的研究。作为稀土资源大国,为了争取我国在国际海底稀土资源竞争中的话语权,维护中国的稀土利益,中国应加紧开展相关的稀土资源勘查和潜力评价。