达里湖沉积粒度组分-湖面状况定量模型

湖泊碎屑沉积物的粒度分布可以提供与区域气候变化相关的湖泊水文变化信息。然而, 由于湖泊沉积物多峰分布固有的复杂性, 其粒度组分成因的解释仍存在很大的不确定性。本文利用对数正态分布函数对内蒙古达里湖36个表层沉积物样品的粒度组分进行了分离, 并探讨了各组分特性与特定沉积环境(包括每个采样点位的离岸距离和水深)之间的关系。结果表明, 达里湖现代碎屑沉积物包含5个截然不同的单峰粒度分布, 分别代表5个不同的粒度组分。虽然其相对百分含量随湖泊水动力条件而变化, 但每个组分均保留着各自的众数粒径、搬运方式、沉积环境等特性。这些组分自细而粗可分为: 长期悬移粘土组分、离岸带悬移细粉砂组分、离岸带悬移中粗粉砂组分、近岸带悬移细砂组分、近岸带跃移中砂组分。近岸带环境两个组分的百分含量与现今湖泊水深呈负相关, 揭示出沉积岩芯近岸带组分与地质历史时期湖面状况相关联的数值模型。该模型在达里湖沉积岩芯中的应用显示, 近岸带组分百分含量增加与同岩芯孢粉序列重建的区域降水减少相对应。两种独立的代用指标在时间上的一致性, 不仅展示了对数正态分布函数分离多峰沉积物的有效性, 而且揭示出利用粒度组分-湖面状况模型重建湖泊古水文的潜力。     

The link between grain‐size components and depositional processes in a modern clastic lake

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.     

A pore-throat model based on grain-size distribution to quantify gravity-dominated DNAPL instabilities in a water-saturated homogeneous porous medium

A pore-scale network model based on spherical pore bodies and cylindrical pore throats was developed to describe the displacement of water by DNAPL. The pore body size and the pore throat size were given by statistical distributions with user-specified values for the minimum, mean and maximum sizes. The numerical model was applied to a laboratory experiment conducted on a sand-filled glass column. The parameters relative to pore body size and pore throat size that were used in the construction of the equivalent network were derived from the discrete grain-size distribution of the real porous medium. The calculated arrival times of the DNAPL front were compared with those measured using optic fibre sensors placed at different points on the control section of the experimental device. Furthermore, the model simulated DNAPL pressure measured at the entrance section of the system. In general, the numerical results obtained with the model were in good agreement with the actual measurements.     

Characterization of clastic rock using a biconcave bond model of DEM

This paper presents a biconcave bond model to investigate the effect of the cementation between grains on the mechanical behavior of rock. The proposed model considers the shape of the bonds among particles that have a biconcave cement form, based on observations of microscopic rock images. The general equations of the proposed model are based on Dvorkin theory. The accuracy and efficiency of the bond model is improved in three ways. After the biconcave bond model is implemented in the discrete element method software Particle Flow Code in 2 Dimensions, a series of numerical uniaxial compression tests were performed to investigate the relationships between the micro‐ to macro‐parameters. The simulations revealed that the biconcave bond model reflects the effect of micro‐parameters, such as the elastic modulus and Poisson's ratio of the cement, on the macroscopic deformation of cemented granular material. Variations in the bond geometry caused extremely diverse macro‐mechanical behaviors. Experimental results concerning rock demonstrate that the biconcave bond model accurately captures the mechanical behavior of intact rock and supports an innovative method for investigating the relationships between the micro‐ and macro‐parameters of cemented granular material. Copyright © 2016 John Wiley & Sons, Ltd.     

Lithification of some modern carbonate sediments in a hypersaline lake adjacent to the Black Sea

In the hypersaline Techirghiol Lake adjacent to the Black Sea, sporadically formed lithified blocks and grapestone are found which are the result of cementation of carbonate sediments with aragonite and possibly kutnahorite (manganesian calcite). The lithified blocks are characterized by a central cavity bordered by a lithified envelope. The formation of the carbonate cement is due to subaquatic bacterial processes of calcium sulfate reduction and the synthesis of calcium carbonate at the expense of gypsum concretions derived from Pleistocene red clays cropping out along the shore of the lake. These lithified blocks have geological significance as they may be usable as criteria for the recognition of sediments deposited in the past near to the shores of hypersaline lakes.     

Multiple drivers of Holocene lake level changes at a lowland lake in northeastern Germany

Many German lakes experienced significant water level declines in recent decades that are not fully understood due to the short observation period. At a typical northeastern German groundwater‐fed lake with a complex basin morphology, an acoustic sub‐bottom profile was analysed together with a transect of five sediment cores, which were correlated using multiple proxies (sediment facies, μ‐XRF, macrofossils, subfossil Cladocera). Shifts in the boundary between sand and mud deposition were controlled by lake level changes, and hence, allowed the quantification of an absolute lake level amplitude of ~8 m for the Holocene. This clearly exceeded observed modern fluctuations of 1.3 m (AD 1973–2010). Past lake level changes were traced continuously using the calcium‐record. During high lake levels, massive organic muds were deposited in the deepest lake basin, whereas lower lake levels isolated the sub‐basins and allowed carbonate deposition. During the beginning of the Holocene (>9700 cal. a BP), lake levels were high, probably due to final melting of permafrost and dead‐ice remains. The establishment of water‐use intensive Pinus forests caused generally low (3–4 m below modern) but fluctuating lake levels (9700–6400 cal. a BP). Afterwards, the lake showed an increasing trend and reached a short‐term highstand at c. 5000 cal. a BP (4 m above modern). At the transition towards a cooler and wetter late Holocene, forests dominated by Quercus and Fagus and initial human impact probably contributed more positively to groundwater recharge. Lake levels remained high between 3800 and 800 cal. a BP, but the lake system was not sensitive enough to record short‐term fluctuations during this period. Lake level changes were recorded again when humans profoundly affected the drainage system, land cover and lake trophy. Hence, local Holocene water level changes reflect feedbacks between catchment and vegetation characteristics and human impact superimposed by climate change at multiple temporal scales.     

基于气候模式统计降尺度技术的未来青海湖水位变化预估

借助于全球气候模式(德国MPI ECHAM5.0)输出信息和流域最近40年的气象观测资料,建立青海湖流域统计降尺度模式(QH-SDM),从而得到流域尺度未来30年(2010-2030年)气候变化情景,并由此驱动水文模型SWAT及湖泊水量平衡模型模拟了青海湖近几十年水位变化过程,预估了未来30年青海湖湖泊水文变化情景。结果表明,青海湖水位的未来变化将经历缓慢下降、逐渐回升、稳步升高3个阶段,到2030年,湖泊水位将达到3195.4 m左右,高出目前水位约2.2 m,面积接近4500 km2,蓄水量达到813亿m3,湖泊恢复到了20世纪70年代初的水平,预计这一结果将会缓解目前青海湖流域水资源紧缺的格局,并有利于植被恢复,减少土地沙化面积,对流域生态环境的改善和国民经济的发展将十分有益。     

A Finnish chironomid- and chaoborid-based inference model for reconstructing past lake levels

In the present study I utilize subfossil chironomid and chaoborid distributions in surface sediments of 68 shallow lakes. The aim is to develop a calibration model for past water-level reconstructions by applying weighted averaging-partial least squares (WA-PLS) techniques and to evaluate its potential applications and limitations. This study considers water depth at sampling sites, rather than maximum lake depth. The best of the water depth models developed uses three components and has a cross-validated coefficient of determination (r²_jack) of 0.68 and root-mean-squared error of prediction (RMSEP) of 0.78 m. The model performance is tested on the sediment sequence of a previously studied lake from southern Finland that is known to have experienced past fluctuations in its water level. The water levels inferred are compared with results of chironomid-inferred air temperature reconstruction to ease separation of the effects of the variables. The reconstruction shows consistent results similar to those of previously published cladoceran planktonic:littoral ratios (P:Ls) from the same lake. However, the results indicate that factors other than depth and temperature, such as pollution, may possibly distort the inference results. The results suggest that in applying the midge-based water depth calibration model, it would be advantageous to use it together with an inference model for temperature and preferably in a multiproxy content where changes in water chemistry may be detected. The model can be useful in studies on past effective moisture variability that is closely related to climatic changes.     

Application of a new computer program for tectonic discrimination of Cambrian to Holocene clastic sediments

TecSand is a new Java software that is used for deciphering the tectonic setting of clastic sediments and sedimentary rocks through two new multidimensional discrimination diagrams. For each sample, TecSand calculates four complex discriminant functions: DF1_m1 and DF2_m1 for the high-silica diagram and DF1_m2 and DF2_m2 for the low-silica diagram, each representing linear combinations of log-ratios of all major elements. These functions determine the position of each sample within island or continental arc, continental rift, and collision/convergent settings. The program also calculates the probability values for the three tectonic fields. TecSand provides a “ready for publication” report for each locality, including the adjusted major elements, log-transformed variables, DF1 and DF2 results, and probability values for individual samples. Validations from samples of known tectonic settings, evaluation of chemical changes, and applications to Precambrian clastic sediments have previously been demonstrated in the literature. Therefore, we illustrate the use of TecSand in 10 case studies covering ages from the Early Cambrian to the Holocene. The results obtained from these two diagrams were not only mutually consistent but also with other geological constraints. As an innovation, TecSand provides an overall synthesis of the two diagrams as total percent probability values. Comparison of the results of this study with the previously published tectonic discrimination diagrams reveals that two recent multidimensional discrimination diagrams are more efficient in discriminating tectonic settings. Although TecSand does provide graphics, which can be imported and modified in commercial software, plotting of the sample diagram is no longer required.     

察尔汗钻孔介形类记录及其对察尔汗古湖晚更新世高湖面的指示

东天山小黄山花岗岩位于阿齐克库都克断裂和康古尔塔格断裂之间的构造带,为一类具有白云母、石榴子石等矿物的S型花岗岩,属于强过铝质花岗岩类。其LA- ICP- MS 锆石U- Pb同位素测年结果为835. 4±9. 0 Ma,地球化学特征说明此花岗岩为后碰撞岩浆作用而成,属于新元古代Rodinia超大陆拼贴- 裂解事件的产物。此外,该前寒武纪岩体的发现结合康古尔塔格—镜儿泉沿线出露的蛇绿岩、含蓝晶石和石榴子石的变质岩系,以及康古尔塔格断裂带南北两侧区域地层的差异,可以将康古尔塔格断裂带作为分隔中天山和北天山构造带的重要依据。     

察尔汗钻孔介形类记录及其对察尔汗古湖晚更新世高湖面的指示

察尔汗盐湖作为柴达木盆地第四纪的沉积中心,沉积了巨厚的第四系湖相沉积,其演化历史研究对于揭示柴达木盆地及青藏高原北部第四纪古气候、古环境演变历史具有重要意义。本文在AMS ¹⁴C测年的基础上,以察尔汗盐湖晚更新世钻孔(ZK53630-1)岩芯中介形类微体化石为研究对象,通过系统的采样和室内分析,共识别出7属10种。基于分类学研究,识别出2个介形类组合(自下而上):Ilyocypris biplicata-Limnocythere inopinata和Ilyocypris bradyi-Ilyocypris sebeiensis。介形类及其伴生化石均显示察尔汗古湖在距今34～28 ka期间的晚更新世晚期(MIS 3a)主体为淡水—微咸水湖泊,气候温暖湿润,与现今极端干旱的盐湖环境截然不同。     

A modification of Burger's phi-normal approximation for the moments of grain-size data

This paper gives a modification of Burger's method of approximation for the moments of grain-size data. It is shown that formal integration can be carried out in conjunction with Burger's phi-normal interpolation scheme. This approach obviates Burger's recourse to a discrete numerical integration procedure because exact integration yields a computationally more efficient approximation formula for the moments.     

An empirical model for estimating hydraulic conductivity of highly disturbed clastic sedimentary rocks in Taiwan

This paper presents the establishment of an empirical HC model for estimating rock mass hydraulic conductivity of highly disturbed clastic sedimentary rocks in Taiwan using high-resolution borehole acoustic televiewer and double packer hydraulic tests. Four geological parameters including rock quality designation (RQD), depth index (DI), gouge content designation (GCD), and lithology permeability index (LPI) were adopted for establishing the empirical HC model. To verify rationality of the proposed HC model, 22 in-situ hydraulic tests were carried out to measure the hydraulic conductivity of the highly disturbed clastic sedimentary rocks in three boreholes at two different locations in Taiwan. Besides, the model verification using another borehole data with four additional in-situ hydraulic tests from similar clastic sedimentary rocks was also conducted to further verify the feasibility of the proposed empirical HC model. The field results indicated that the rock mass in the study area has a conductivity between the order of 10^− 10 m/s and 10^− 6 m/s at the depth between 34 m and 275 m below ground surface. Results demonstrate that the empirical HC model may provide a useful tool to predict hydraulic conductivity of the highly disturbed clastic sedimentary rocks in Taiwan based on measured HC-values.     

The response of lake margin sedimentary systems to climatically driven lake level fluctuations: Middle Devonian,Orcadian Basin,Scotland

Lake margin sedimentary systems can provide highly sensitive records of sedimentary response to climate change. The Middle Old Red Sandstone of Northern Scotland comprises a thick succession of cyclic lacustrine sediments. Within this succession the deepest lake phase, the Achanarras fish bed, allows bed‐scale correlation over 160 km across the basin. This provides a unique opportunity to examine the character of synchronous lake margin deposits, and their response to climatically driven lake level fluctuations, across a large continental basin. Detailed characterization of two separate lake margin systems was carried out utilizing multiple sections in western Orkney, in the north, and Easter Ross, in the south. Seven facies have been recognized, which include upper and lower shoreface, deep lake, shallow lake, playa, turbidite and fluvial facies. Differences in vertical and lateral facies stacking patterns reflect the response of these systems to climatically driven fluctuations in lake level. Comparison of the northern and southern systems examined highlights the variable response of lake margin systems to the same climatic change and related lake level fluctuations. In the south, a greater fluvial influence is recognized on the development of the lake margin successions, whereas in the northern example, which lay on the downwind margin of the lake, shore zone facies are more commonly developed. The variability recognized can be accounted for by regional variations in sediment supply, coastal physiography, lake size, bathymetry and potential fetch. Lake level stability is also recognized as a major control on the development of lake margin sedimentary systems, as is the linked or unlinked relationship of the catchment and the lake basin climate for which a conceptual model is proposed.     

A time-space model for the distribution of shoreline archaeological sites in the lake superior basin

Archaeological site interpretation can be enhanced by consideration of related geological and geomorphological processes. Lake Superior has a history of glaciation, isostatic recovery, and water-level change. Two examples are given of shoreline sites at which interpretation is enhanced by an understanding of local geologic factors. The archaeologic history of the Lake Superior basin is reviewed, and three cultural traditions are recognized; (1) Paleoindian, (2) Archaic, and (3) Woodland. Three significant factors of geologic history are then discussed: (1) ice margin oscillation, (2) differential isostatic uplift, and (3) lake-level fluctuations. The factors reducing or improving shoreline archaeological site preservation are examined, and a summary model of shoreline site distribution for the Lake Superior basin is offered. It is concluded that the north shore provides the best potential for a complete archaeological record. © 1993 John Wiley & Sons, Inc.     

Techniques to measure grain-size distributions of loamy sediments: a comparative study of ten instruments for wet analysis

Ten instruments for measuring the grain‐size distribution of loamy sediments in water were tested in a comparative study. Instruments tested were: the Malvern Mastersizer S, the Coulter LS 200, the Fritsch Analysette 22 (version C), the Horiba Partica LA‐950, the Sedigraph 5100, the Atterberg cylinder, the Coulter Multisizer 3, the CIS‐100, the EyeTech and the image analysis software Histolab. The first four instruments use laser diffraction. The Sedigraph and Atterberg cylinder are based on sedimentation. The Coulter Multisizer 3 uses impedance measurements and the last three instruments use optical techniques. Grain‐size analyses were carried out on four sediments with median grain diameters of approximately 35, 30, 12 and 9 μm, respectively, and with no particles >90 μm. The laser diffraction instruments produced the best results for the various criteria considered in this study, followed by the Coulter Multisizer 3 (electrical sensing zone technique), the sedimentation techniques and the optical methods. However, the study also showed that there is no such thing as an ‘ideal’ method because techniques may score differently according to the criterion tested. An appropriate evaluation thus requires that various criteria be considered. Issues to be taken into account are: type of sediment, quantity of sediment available, speed of measurement, complexity of the measurement protocol, processing of the data, reproducibility of the results and the specific aims of the study undertaken.     

Some methods for statistical analysis of multimodal distributions and their application to grain-size data

Some of the methods used in the resolution of mixed normal distributions are discussed under three headings: analytical, graphical, and numerical methods. Attention is given to their applicability in the analysis of grain-size data as derived from sieving. Comparisons are made by applying several methods to published data. It is concluded that the numerical methods offer most scope, especially the method of nonlinear least squares. Some analyses of beach sediments, using this method, are presented. The adoption of a convention for the number of individuals in the sample increases ease of interpretation.     

Turbidites and iron formations, Beardmore-Geraldton, Ontario: application of a combined ramp/fan model to Archaean clastic and chemical sedimentation

Sandy turbidites, grain flows, conglomeratic mass-flows and oxide-facies iron formation are present in the late Archaean Beardmore-Geraldton terrain, a metasedimentary belt which extends for at least 80 km in an E-W direction. The marine portion of this basin contains four lithofacies associations (LA): (1) Thinbedded, iron formation-clastic sediment association. This association represents a continuum of deposit types containing iron formation; subtypes are defined on the basis of bedding attributes and the proportion of iron formation to sand/silt. (2) Thin-bedded, turbidite-dominated association. These sediments consist mostly of silt/sand beds which either show no vertical trends, or thin and fine upwards over a few metres. (3) Medium-bedded, turbidite-dominated association. Most of these sediments are medium to coarsegrained, vertically unstructured sand sequences with occasional structured intervals. (4) Thick-bedded association. This is dominated by poorly graded sands up to 7–8 m in thickness. Sand beds are characterised by a thin basal zone of coarse sand and pebbles, a large central interval containing a mixture of medium and coarse sand, and a thin upper zone of fine sand/silt. The overall depositional system was initiated by transport of sediment by braided streams to the strand area where it accumulated in distributary mouth bars. We infer a nearshore break in slope, locally with large channels (LA 4) extending from close to the strand line across deltaic surfaces to the deeper portions of submarine fans (structured portions of LA 3). However, many deltaic surfaces probably were not tapped by major channels, but merged downslope into a submarine ramp. Sediment was transported across the ramp by slump events and sheet-like grain flows (unstructured portions of LA 3). Iron formation and LA 2 sediments probably accumulated both in upper-mid ramp areas with low sediment delivery rates, and distal to fan-ramp successions. As major streams on the braid plain changed position, associated submarine channels and slump-fed ramp deposits also would have shifted laterally. This produced overlap of different facies associations in both the fan and ramp environments, which may explain why observed vertical trends in bedding are limited to several metres. We suggest that on narrow, active Archaean cratonic margins, additional non-regular processes such as variations in sediment supply related to periods of heightened pyroclastic activity, and seismic activity associated with the arc, also contributed to the lack of vertically structured sequences. Turbidite sequences in such environments in general may contain important contributions from both submarine ramp and submarine fan sedimentation.     

Evaluating trophic status and restoration procedures of a polluted lake,Lake Kastoria,Greece

Lake Kastoria is a shallow lake with many anthropogenic activities concentrated in its catchment area. Surficial runoff rich in agricultural waste and underground seepage from urban and rural areas enrich the lake with nutrients intensifying the eutrophication problem of the water.Restoration techniques, with different approach, each one are proposed to restore the lake water. Treatment with alum is very effective but needs special care during the application. Reeds harvesting is an inexpensive and effective way and in combination with the city sewage redirection will improve the water quality and the trophic status of the lake sufficiently.