Late Pleistostene-Holocene sedimentation in lakes of central Transbaikalia: Implications for climate and environment changes

We present integrated mineralogical, geochemical, and palynological data for Late Pleistocene-Holocene bottom sediments of Lake Arakhlei located in the Beklemishev tectonic basin in the southern Vitim Plateau (central Transbaikalia). The sediment samples were studied by X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) spectroscopy, laser particle sizing, spore-pollen analysis, radiocarbon (¹⁴C AMS) dating, and XRF spectrometry. The cored 128 cm long section of lake sediments consists of two units: One is composed mainly of layered silicates (illite-smectite, illite, chlorite, chlorite-smectite, muscovite, and kaolinite) and organic matter (OM) but no carbonates from 0 to 80 cm and the other contains authigenic Ca-Mg carbonates (up to 30%) of Mg-calcite and excess-Ca dolomite from 80 to 128 cm. The sediments also contain a rare mineral weddellite CaC₂O₄2H₂O discovered for the first time in Transbaikalian lakes. The evolution of Lake Arakhlei and its drainage basin comprised four stages, with pollen zones that mark the Late Pleistocene and Holocene climate history of the Beklemishev basin. The reconstructed history of Lake Arakhlei for the past ~ 15,500 years followed general climatic changes in the Northern Hemisphere. Thus, integrated research, including detailed analysis of mineral components and spore-pollen assemblages in lake sediments, is a workable tool for studying climatic controls of continental sedimentation.     

Evaluation of two multidimensional discrimination diagrams from beach and deep-sea sediments from the Gulf of Mexico and their application to Precambrian clastic sedimentary rocks

Two discriminant-function-based multidimensional major-element diagrams for the tectonic discrimination of siliciclastic sediments were recently published from a coherent statistical methodology of log_e-ratio transformation and linear discriminant analysis. These diagrams were constructed based on worldwide examples of Neogene–Quaternary siliciclastic sediments from known tectonic settings. In this work, these two tectonic discrimination diagrams were first successfully tested from Holocene (<0.0117–0 Ma) beach and deep-sea sediments from the Gulf of Mexico. These diagrams were used to decipher tectonic settings of 11 case studies of the Precambrian clastic sedimentary rocks (~512–2800 Ma) from Argentina, USA, Ghana, Spain, Norway, India, China, and Australia. The test and application results obtained from these discrimination diagrams were generally consistent with the geology of the Precambrian source areas. Therefore, the two multidimensional diagrams can be considered as a useful tool for successfully discriminating the tectonic setting of older sedimentary basins, which may consist of one or more tectonic assemblages. Comparison of results of this study with the previously published tectonic discrimination diagrams is illustrated and the probable reasons for some inconsistent inferences were also discussed.     

Reconstructing 4000 years of mass movement and tsunami history in a deep peri‐Alpine lake (Lake Geneva,France‐Switzerland)

The study of mass movements in lake sediments provides insights into past natural hazards at historic and prehistoric timescales. Sediments from the deep basin of Lake Geneva reveal a succession of six large‐scale (volumes of 22 × 10⁶ to 250 × 10⁶ m³) mass‐transport deposits, associated with five mass‐movement events within 2600 years (4000 cal bp to 563 ad ). The mass‐transport deposits result from: (i) lateral slope failures (mass‐transport deposit B at 3895 ± 225 cal bp and mass‐transport deposits A and C at 3683 ± 128 cal bp ); and (ii) Rhône delta collapses (mass‐transport deposits D to G dated at 2650 ± 150 cal bp , 2185 ± 85 cal bp , 1920 ± 120 cal bp and 563 ad , respectively). Mass‐transport deposits A and C were most probably triggered by an earthquake, whereas the Rhône delta collapses were likely to be due to sediment overload with a rockfall as the external trigger (mass‐transport deposit G, the Tauredunum event in 563 ad known from historical records), an earthquake (mass‐transport deposit E) or unknown external triggers (mass‐transport deposits D and F). Independent of their origin and trigger mechanisms, numerical simulations show that all of these recorded mass‐transport deposits are large enough to have generated at least metre‐scale tsunamis during mass movement initiation. Since the Tauredunum event in 563 ad , two small‐scale (volumes of 1 to 2 × 10⁶ m³) mass‐transport deposits (H and I) are present in the seismic record, both of which are associated with small lateral slope failures. Mass‐transport deposits H and I might be related to earthquakes in Lausanne/Geneva (possibly) 1322 ad and Aigle 1584 ad , respectively. The sedimentary record of the deep basin of Lake Geneva, in combination with the historical record, show that during the past 3695 years, at least six tsunamis were generated by mass movements, indicating that the tsunami hazard in the Lake Geneva region should not be neglected, although such events are not frequent with a recurrence time of 0·0016 yr^?1.     

三氯化铝浸取-火焰原子吸收光谱法测定水系沉积物中低含量的碳酸铁

传统的氯化铵浸取-重铬酸钾滴定法(邻二氮菲比色法)可有效分析试样中较高含量的碳酸铁(7.5%~80%),但试剂消耗量大、测定步骤冗长、分析误差相对较大,水系沉积物中碳酸铁含量较低,采用此方法分析时其他含铁矿物的干扰易引入测量误差。本研究采用三氯化铝水浴加热浸取,建立了火焰原子吸收光谱法(FAAS)测定水系沉积物中低含量碳酸铁(0.1%~6.0%)的分析方法。使用80 m L浓度为100g/L的三氯化铝溶液水浴加热60 min,可完全浸取试样中的碳酸铁;在标准曲线中加入与待测样品浓度相同的三氯化铝,有效地避免了浸取剂三氯化铝的基体干扰。碳酸铁的检出限为0.015μg/m L,精密度为2.3%~4.0%(n=12),加标回收率为95.0%~107.5%。沉积物中常见的含铁矿物(如赤铁矿和磁铁矿)对碳酸铁的测定干扰可忽略,磁黄铁矿的干扰可通过加入氯化汞消除。本法比传统化学分析方法的操作简便,准确度和精密度高,解决了其他含铁矿物的干扰问题。     

Lacustrine Arcellinida (testate lobose amoebae) as bioindicators of arsenic concentration within the Yellowknife City Gold Project,Northwest Territories,Canada

Arcellinida (testate lobose amoebae) were examined in near-surface sediment samples from 30 lakes located within the Gold Terra Resource Corporation (GTRC) Yellowknife City Gold Project, Northwest Territories, Canada, to assess the applicability of using the group as a robust tool to assess Arsenic (As) contamination. Lake contamination by As is of concern in the Yellowknife area because it is derived from geogenic (bedrock) and anthropogenic sources (legacy pollution from former mining operations, particularly the Giant Mine [1948–2004]). Statistical multivariate analyses (cluster analysis, non-metric multidimensional scaling [NMDS], and redundancy analysis [RDA]) were performed on geochemical (inductively coupled plasma mass spectrometry [ICP-MS]) and organic (loss-on-ignition) data to identify geochemical and hydrogeological controls on the arcellinidan distribution in the lakes. Three distinct faunal assemblages were identified using Cluster analysis and NMDS: 1) Elevated Arsenic Assemblage (EAA; Approximately Unbiased (AU) p-value = 97 %; median As =272.4 mg/kg, range = 42–1353 mg/kg ; n = 9); 2) Centropyxid-Dominated Assemblage (CDA; AU p-value = 87 %; median As =169.7 mg/kg, range 60–233 mg/kg ; n = 9); and, 3) Difflugiid-Dominated Assemblage (DDA; AU p-value = 95 %; median As =61.3 mg/kg, range = 16–316 mg/kg ; n = 12). Six statistically significant controls on assemblage structure were identified using RDA. These were As, calcium, iron, strontium, water depth, and total organic carbon (Arcellinida variance explained = 36.2 %) — As is the most significant control (12.2 %; p-value < 0.002). Stress-tolerant centropyxids dominate in lakes characterized by elevated sedimentary As concentrations (64 % centropyxids in EAA; 40 % centropyxids in CDA), while stress-sensitive taxa thrived in samples associated with lower As concentrations (DDA). Our results corroborate the findings of previous Arcellinida studies in subarctic Canada and confirms the reliability of using Arcellinida as a reconnaissance tool for tracking As contamination in impacted lakes.     

Accumulation of polychlorinated biphenyls (PCB) associated with bottom sediments in larvae of Chironomus riparius Meigen

Patterns of bioaccumulation of polychlorinated biphenyls (PCBs) by chironomid larvae (Chironomus riparius Meigen) were studied under laboratory conditions. Larvae were maintained for 20 days, separately in two batches of natural bottom sediments sampled from Rybinsk Reservoir (Russia), each differing in PCB content (425.6 μg / kg or 24.8 μg / kg dry weight, respectively). The study revealed that chironomid larvae accumulated PCBs at levels comparable to the PCB content measured in sediments from each exposure. The bioaccumulation coefficient (1.11 and 1.59, respectively, as per dry weight for compared sediment batches) depended directly on the sum PCB content in sediments. At high sediment PCB content, the ratios of homologous groups of PCBs in larvae and sediment were identical and corresponded to the Aroclor 1254 congeners profile; at lower PCB content, pronounced differences were revealed. In larvae, the ratios of 3, 4, 5, and 6CB homologues were evenly distributed at levels of 20–34 %, while the 4CB homologues prevailed (47 %) in sediments. The content of the latter compounds in larvae was lower than in sediments, and higher for the other homologous groups. The study indicates selective bioaccumulation of various homologous groups of PCBs under conditions of low sediment PCB content.     

年轻沉积物36Cl测年研究进展

宇宙成因核素36Cl对第四纪地层及第四纪时代的厘定具有独特的优势.近年来随着加速器质谱(AMS)技术的不断发展,36Cl已经能被高灵敏测量,使得36Cl测年技术前景广阔.本文介绍了36Cl测年的研究现状和研究难点,对于陆相沉积物的36Cl测年方法进行了探索,对制约其发展的测年公式中早期放射性比度I0对测年精度的影响以及在地球科学中的应用前景进行了探讨,进一步提出不同海拔高度对I0存在叠加效应.同时介绍了36Cl样品的制备流程,该流程采用离子交换树脂驱除试样中的硫和可能产生“盐效应”的常量金属元素,有效地排除了36S对36Cl的干扰,建立了动态的AgCl制样技术流程,方法高效快捷.     

Grain-size distribution,morphoscopy and elemental chemistry of suspended sediments of Pindari Glacier,Kumaon Himalaya,India

Abstract

Suspended sediment concentrations in the meltwater of Pindari Glacier were determined at regular intervals in four ablation seasons. The late ablation periods (September 1994 and October 1995) were characterized by a reduced level of sediment concentration, while the sampling periods of early ablation (May 1994 and July 1995) showed very high concentrations of suspended sediment in the meltwater. Grain size distribution shows the dominance of medium and coarse silt fractions of the mean size of the suspended sediments between 4.35 and 5.82 ø. Clay size constitutes about 7% of the total size population. The majority of the samples are poorly sorted, symmetrically to finely skewed and mesokurtic in nature. The grain shows texture of mechanical and chemical origin, in which mechanical texture is predominant on most of the grains. It was observed that the grains were mostly subangular to subrounded in shape with variable size ranges. Bulk sediment chemistry consists mostly (>70%) of the five elements, Si, Al, K, Fe and Mg. Iron (Fe) and Mn are dominant heavy metals and sediments show the elemental abundance in the order of Fe > Mn > Zn > Cu > Ni > Pb. The Chemical Index of Alteration (CIA) of suspended sediments (57) is relatively higher than in the case of average unweathered upper continental crust (~50) indicating a higher degree of weathering due to glacier grinding and crushing action. Quartz is the most dominant mineral, followed by mica, illite, feldspar and kaolinite.     

Distributions and vertical variation patterns of sound speed of surface sediments in South China Sea

The distributions of sound speed show different characteristics in continental shelf, continental slope and Nansha Trough. The differences have closely related to the distributions of sediment physical properties in the southern South China Sea. According to the analysis of sound speeds and physical properties variation characteristics with buried depth, the vertical variations of sound speed are closely related to sediment texture, sedimentary environment, transport, erosion, compaction, consolidation, etc. The comparison results indicate 3 vertical variation patterns of sound speed: increasing model, invariant model and complicate variation model. The above 3 variation models represent the vertical distribution characteristics of sound speed in different depositional environments. Different variation patterns have different key factors which generally contain porosity or grain size. The calculated sound speeds with Buckingham’s theory of compressional waves in fluid-like marine sediments follows the trend of measured speeds accurately.     

Analysis of ore-bearing properties of major stratigraphic units in Harlik area of Xinjiang Province

The Harlik metallogenic belt is a favorable area for polymetallic mineralization of Cu,Au, W, Sn, Mo, Fe, Mn, Ni and Co. In order to further study the ore-bearing properties of each stratum in the metallogenic belt, based on the 1:50 000 stream sediment measurements in Hami area of Tianshan Mountains, the authors analyzed the characteristic parameters, distribution and evolution of 17 elements, and the ore-bearing properties of 7 stratigraphic units. The results show that Au, Sb and Bi are of extremely uneven distribution (C_v≥1.5), and As, Hg and W are of uneven distribution (1.5>C_v≥1.0). There are four distribution types of elements in the region: symmetry, positive bias, negative bias and bimodal. The concentration coefficients of these elements and oxides show a wavy and tortuous change in each stratigraphic unit. Iron group elements are mainly enriched in Daliugou Formation and Tousuquan Formation. Tungsten and molybdenum group elements are mainly enriched in Tousuquan Formation. Au is mainly enriched in Daliugou Formation and Dananhu Formation. Au, Cu, W, Bi, Fe, Mn and Zn are the dominant mineral resources in the study area after comprehensive analysis. And the main mineralizing elements are Au, Cu and Fe, and their optimum enrichment age is Ordovician, followed by Devonian. The Daliugou Formation of Ordovician is the main ore-bearing stratum.