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生物硅（biogenicsilica）是湖泊沉积物的重要组成部分,它绝大部分来源于湖泊硅藻壳的沉积,其产率变化反映了湖泊区域气候环境的变化,因而近年来成为国际上追踪和探寻古气候环境变化的又一种新的有效手段。生物硅的研究过去主要集中于海洋沉积物上,并建立了7种生物硅测量方法：直接X射线衍射法、间接X射线衍射法、红外分光洁、全岩化学元素计算法、差异湿法、微体化石计数法和碱溶分光光度法。我们在碱溶分光光度法基础上作了部分改进,初步建立了湖泊沉积生物硅实验室测定方法,硅胶模拟实验表明该方法准确可靠,沉积样品重复性测量误… 相似文献
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青海湖沉积物生物硅的环境意义初步研究 总被引：1，自引：0，他引：1
湖泊沉积物中生物硅含量的变化已经被广泛应用于评价湖泊生产力和古气候变化研究,但大型湖泊不同位置生物硅含量的时空变化及其与环境要素之间的关系仍缺乏详细的现代过程研究.通过对青海湖不同位置表层沉积样品的生物硅含量测定,建立其空间分布模式及最近数百年生物硅含量的时间序列.结果表明,青海湖表层沉积物生物硅含量变化范围是1.75%～2.98%,平均值为2.25%.与世界其他湖泊相比,青海湖生物硅含量处于相对较低水平,可能与其特殊的地理位置和气候条件有关.青海湖生物硅含量的空间分布规律与沉积物质量堆积速率以及陆源组分含量(如SiO2)相反,而与化学/生物沉积组分(如CaCO3)含量的空间分布规律大体一致,说明生物硅的空间分布受到陆源碎屑物质的"稀释效应"影响.时间序列上,生物硅含量与SiO2含量呈相反变化趋势,与指示降雨量变化的C/N比值也是反相变化,说明生物硅含量在时间序列上也受与气候条件密切相关的陆源输入的影响.青海湖湖心低沉积速率区域的生物硅指标具有指示古气候变化的潜力. 相似文献
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江西东乡矿区沉积硅质岩的地球化学特征和成因 总被引：9，自引：2，他引：9
江西东乡矿区石炭系地层中存在三层与地层整合产出的层状硅质岩。硅质岩富Ｆｅ，Ａｓ，Ｓｂ，Ｂｉ和Ｇａ；稀土元素总量低，Ｃｅ呈弱负异常，重稀土相对富集，δ＾３０Ｓｉ值变化范围为０．５‰－０．８‰，δ＾１８Ｏ变化范围为１２．５４‰－２１．１１‰。硅质岩地球化学特征表明其成因为介于热水沉积与生物沉积之间的过渡类型。 相似文献
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湘川地区震旦-寒武系硅岩的有机岩石学研究 总被引：9，自引：0，他引：9
湘川地区包括四川秀山、相西和湘中地区。该地区震－寒武系层状硅岩发育。硅岩有机碳含量较高，变化于０.０６～９.００％，平均１。５７％。有机碳与某些微量元素（Ｂａ、Ｚｎ、Ｒｂ、Ｃｏ、Ａｓ、Ｕ、Ｔｈ）的线性关系不明显；油浸显微镜下鉴定硅岩中的干酪根组成多为有机质碎片和微粒体，并显示微弱的各向异性。原始母质类型经恢复后基本为腐泥型，属于Ⅰ型无定型干酪根；在干酪根化学元素组成图上（ＶａｎＫｒｅｖｅｌａｎ图），均位于变生作用阶段区，表明有机质成熟度高；干酪酪根稳定碳同位素组成变化于－２９.３０～－３５.８４％。上述有机岩石学特征分析表明，生物及其降解产物－有机质对硅岩的形成具有不可忽视的贡献；硅岩形成过程中可能发生过“去杂质”作用；硅岩中的有机质成熟度较高；硅岩的形成环境可能属于浅水陆缘滞流盆地。 相似文献
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湘黔桂地区晚前寒武纪层状硅质岩地球化学特征及成因 总被引：8，自引：0，他引：8
湘黔桂地区晚前寒武纪发育厚度较大的层状硅岩层,岩石化学成分纯净、硅质矿物含量９５％以上,岩石贫微量元素,但富Ｂａ、Ａｓ、Ｓｂ、Ａｇ、Ｕ元素;稀土元素总量低;Ｃｅ呈明显的负异常,轻稀土含量大于重稀土含量;δ＾３０Ｓｉ值变化为０．０￣０．７‰,ε＾１８Ｏ值变化范围为２０．１￣２３．６‰。硅质岩地球化学特征表明其成因为介于热水沉积与生物沉积之间的过渡类型。 相似文献
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梅河盆地沉积体系及沉积体系域 总被引：2，自引：0，他引：2
梅河盆地是抚顺──密山深大断裂南段的组成部分，是一个典型的断陷型聚煤盆地。根据钻探、测井和粒度分析等资料，对沉积体系和沉积体系域进行了分析，梅河盆地主要沉积体系有冲积扇－扇三角洲沉积体系、湖泊沉积体系和河流－三角洲沉积体系，每一种沉积体系都由一套有规律的沉积组合构成。随着盆地的演化，梅河盆地先后出现了冲积扇－辫状河、冲积扇－扇三角洲－湖泊、河流－三角洲一湖泊等沉积体系域。 相似文献
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东川落雪式铜矿的含铜“礁—硅岩组合与海底喷流热液成矿 总被引：1，自引：0，他引：1
从区域地质背景，岩石学，岩石化学，微量元素，氧同位素及稀土元素组成等方面论证东川铅矿含铜“礁－硅岩组合”中的含铜硅质条带－硅质白云岩为海底喷流热水沉积成因；提出了该类层状铜矿的深源含铜富硅混合热液海底喷流－生物富集的沉积成岩成矿模式，并提出了东川落雪层状“马尾丝”铜矿合矿岩系为“含铜礁－硅岩组合”的新观点。 相似文献
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从生物扰动构造看古近纪东营湖的湖水分层 总被引：3，自引：0，他引：3
生物扰动构造发育程度与湖水充氧条件及湖水分层有密切关系。通过对山东东营凹陷下第三系 5套油源岩的生物扰动构造进行分析 ,分别讨论了其沉积时期古湖泊水体的分层状况。富有机质纹层页岩中无生物扰动构造 ,生物扰动指数为 0 ,表明其沉积时为一稳定分层、底层水缺氧的古湖泊 ;钙质块状纹层泥岩中含显微生物扰动构造 ,主要分布在细粒方解石纹层中 ,生物扰动指数为 1,反映较稳定分层、缺氧但有短暂充氧的沉积环境 ;钙质纹层页岩中显微生物扰动构造可局部富集呈层 ,生物扰动指数为 1～ 2 ,反映当时古湖泊有季节性回水 ,含氧量呈季节性变化 ;红、灰条带状粉砂质泥岩肉眼即可观察到生物扰动构造 ,主要分布在红色层中 ,生物扰动指数为 2～ 3,反映为不分层、充氧的古湖泊环境 ;块状泥岩扰动最为强烈 ,生物扰动指数为 6 ,表明为不分层、充氧的沉积环境 相似文献
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A case study of the Chudsko-Pskovskoje Lake (located some 200 km SW of Leningrad), the largest shallow-water lake in Europe, describes individual links in the trophic chain and their dependence on hydrological factors which control the eutrophication process. Current systems within the lake are modelled numerically, using a three-dimensional model of non-stratified currents. Results of modelling are confirmed by generalized field measurements. Nutrient and biotic conditions in the lake are described and ways of preventing eutrophication are discussed. 相似文献
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Natural Hazards - Glacial lakes are rapidly growing in response to climate change and glacier retreat which may lead to catastrophic socio-economic disasters. The failure of moraine-dammed lakes is... 相似文献
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Cores of soft lake sediments 总被引：5，自引：0，他引：5
Short cores of soft sediment, used in studying the pollution history of lakes, can be obtained with a plastic tube fitted with a piston and piston wire. If the sediments of deep water are annually laminated (and thus difficult to sample without disturbance) or contain excess gas (which can disrupt the stratigraphy during its escape), a short 'core' can be acquired by producing a frozen crust on a tube filled with dry ice and butanol.
A continuous core of soft lake sediment at least 7 m long can be obtained in a single drive beneath deep water with a hand-driven piston corer. Such a core assures the complete continuity necessary for counting annual laminations or for making close-interval analyses without fear of gaps, and it provides the uniform orientation required for measurements of paleomagnetic directions. 相似文献
A continuous core of soft lake sediment at least 7 m long can be obtained in a single drive beneath deep water with a hand-driven piston corer. Such a core assures the complete continuity necessary for counting annual laminations or for making close-interval analyses without fear of gaps, and it provides the uniform orientation required for measurements of paleomagnetic directions. 相似文献
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Elisabeth Dietze Michał Słowiński Izabela Zawiska Georg Veh Achim Brauer 《Boreas: An International Journal of Quaternary Research》2016,45(4):828-845
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. 相似文献
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Grain-size distributions of fluvial, eolian and marine sediments were explicated decades ago. For lake sediments, however, there is still great uncertainty in explaining the genesis of grain-size components due to the inherent complexity of their polymodal distributions. In this study, the grain-size components of the surface sediments of Daihai Lake, Inner Mongolia, were partitioned using a lognormal distribution function and the relationship between the identity of each component and the specific sedimentary environment was investigated. The data indicate that the modern clastic sediments of Daihai Lake contain five distinct unimodal grain-size distributions representing five 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 condition 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 and saltation medium sand. The percentage of the components interpreted as an indication of nearshore environments displays a negative correlation with water depth across the modern lakebed, suggesting a model for linking the nearshore components in sediment cores to the lake level status in the geological past. The model was applied to a sediment core from the lake where high percentages of the nearshore components in the core sediments were correlated with low regional precipitations reconstructed on the pollen profile of the same core. The coincidences between two independent proxies do not only demonstrate the validity of lognormal distribution function in partitioning polymodal sediments but also reveals the potential of the grain-size component–lake level status model for lake’s paleohydrological reconstruction. 相似文献
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Julie C. Aleman Audrey Saint-Jean Bérangère Leys Christopher Carcaillet Charly Favier Laurent Bremond 《Quaternary Research》2013
So far, no phytolith extraction protocols have been tested for accuracy and repeatability. Here we aim to display a phytolith extraction method combining the strengths of two widely used protocols, supplemented with silica microspheres as exogenous markers for quantifying phytolith concentrations. Phytolith concentrations were estimated for samples from two sedimentary sequences in which numerical age–depth models make it possible to calculate phytolith influxes (phytolith numbers per cm2per yr). Analysis of replicates confirmed the statistical robustness, the repeatability and the very few biases of our extraction technique for small phytoliths, since the relationship between grass silica short cells and microspheres was kept stable. Furthermore, we demonstrated that silica microspheres are robust exogenous markers for estimating phytolith concentrations. The minimum number of items (i.e., phytoliths plus silica microspheres) that must be counted to estimate phytolith concentrations and thus influxes depends on the ratio of phytoliths to microspheres (R) and is minimized when R = 1. Nevertheless, we recommend using ratios R ≤ 1 in order to avoid having the counting process become excessively time-consuming, because microspheres are easier to identify and count than phytoliths. 相似文献
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Trace fossils from proglacial lake sediments 总被引：1，自引：0，他引：1
PHILIP L. GIBBARD ANTHONY J. STUART 《Boreas: An International Journal of Quaternary Research》1974,3(2):69-74
Trace fossils have been discovered in Middle Pleistocene proglacial lake sediments from St. Albans, Hertfordshire, England. They indicate that this environment was capable of supporting a variety of benthonic animals. The fossils are described and tentatively assigned to several invertebrate groups. 相似文献
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Mercury contribution to an adirondack lake 总被引：1，自引：0，他引：1
Elevated copper, lead, and zinc concentrations in the upper 10 to 20 cm of sediment sampled from Cranberry Lake, a large Adirondack
lake, are attributed to atmospheric contributions. Pb-210 and pollen core data, however, suggest Cranberry Lake also received
mercury discharges during the turn of the century when the area was the center of extensive lumbering and related activities.
Elevated mercury concentrations in Cranberry Lake smallmouth bass derived from remobilization from mercury-contaminated bottom
sediments which increased the bioavailability to Cranberry Lake organisms. Mercury remobilization and accumulation by fish
are promoted by fluctuating pH values resulting from acid precipilation. 相似文献