河南西峡盆地上白垩统河流及湖泊沉积中的遗迹组构

河南西峡盆地上白垩统马家村组沉积厚度巨大,达1 960 m,由辫状河沉积、曲流河沉积和湖泊沉积组成。在河流与湖泊沉积中,发育丰富的遗迹化石,共6种类型,分别为Skolithos linearis、Cylindricumichnosp、Palaeophycus tubularis“J”形潜穴、垂直分枝潜穴和垂直螺旋潜穴。从形态分析,大多数为居住迹,按照遗迹化石产出岩层的岩性、扰动特征和残留遗迹等总体特征,将所发现的遗迹化石层划分为两类遗迹组构,即软底组构和僵底组构。前者主要发育在纹层状极细砂岩和粉砂岩中,潜穴密度大,属种单一,包括Skolithos组构和Palaeophycus组构;后者主要发育在厚层泥岩中,潜穴密度较大,类型稍多,包括由Cylindricum ichnosp、垂直分枝潜穴J形潜穴和垂直螺旋潜穴所组成的遗迹组构。与报道过的其他地区陆相遗迹化石的对比表明,随着时间的推移,河流沉积中的组构特征在白垩纪有明显变化,而浅湖沉积中的遗迹组构表明造迹生物的扰动能力显著加强。     

Thallium diagenesis in lacustrine sediments

Dated sediment cores and porewaters from two Canadian Shield lakes, located 40 km from Québec City (L. Tantaré) and 25 km downwind from an important smelter in northwestern Québec (L. Vose), were analyzed for thallium and other geochemical variables. Atmospheric deposition is the only source of anthropogenic Tl to these lakes. The porewater Tl concentration profiles in L. Tantaré display a peak below the sediment-water interface that suggests post-depositional Tl remobilization and transport to the overlying water and deeper sediments; such a dissolved Tl peak occurs just above the sediment-water interface in L. Vose. Modeling the porewater Tl profiles with a diagenetic reaction-transport equation reveals a zone of dissolved Tl production lying above a zone of Tl consumption in L. Tantaré sediments. In contrast, in L. Vose, Tl diffuses across the sediment-water interface from the anoxic hypolimnion and is fixed to the surficial sediments. The localization of the consumption zones, the shape of the dissolved Tl, sulfide and iron profiles, as well as calculations of saturation states are all consistent with the removal of Tl from porewater by co-precipitation with and/or adsorption to Fe sulfides. The concentrations of Tl removed from or added to sediments after their deposition (i.e., diagenetic Tl) amount to up to 36% of measured sediment Tl concentrations. Comparison of the reconstructed historical Tl records with those of polycyclic aromatic hydrocarbons (PAHs) and of Pb originating from coal burning or from smelting activities indicate that coal combustion is the major source of atmospheric Tl to L. Tantaré and that an additional important Tl source to L. Vose is the nearby smelter.     

松辽盆地白垩系青山口组核形石的发现及其环境意义

在松辽盆地上白垩统青山口组中首次发现核形石灰岩,见于细砂岩、粉砂岩和泥质岩层系中。核形石有三种类型：环状、石笋状和姜状核形石。多数核形石由核心和多环纹层组成,少数具不明显核心或呈单层环状。该套核形石形成于湖泊三角洲前缘分流河口砂坝侧翼的水下分流间湾环境。地形坡度和三角洲前缘的生长,致使核形石普遍发生准同生变形。由于核形石出现于青山口组二、三段,处于温湿向干热气候转变时期,因此核形石可能作为重要的古气候变迁标志。     

Selective chemical extraction of carbonate-associated metals from recent lacustrine sediments

Acidic ion-exchanger was applied to the selective extraction of heavy metals in carbonate phases of recent lake sediments. Cr was not detected and Fe and Cu contents were reduced by factors of three to ten, relative to non-carbonate fractions of the sediment samples. Values obtained for Mn and Zn exemplify the effects of dilution was well as enrichment, both originating from increased carbonate percentages. Determinations on grain-sized fractions from Bodensee samples suggest that elevated inputs of dissolved Zn, which partly originate from human activities, may be immobilized by authigenic carbonate precipitation.     

Long-chain unsaturated ketones in recent lacustrine sediments

C₃₇–C₃₉ ketones containing 2–4 double bonds and similarly-unsaturated C₃₈–C₄₀ ethyl ketones have been detected for the first time in lacustrine sediments. Tetra-unsaturated compounds are relatively more abundant than in marine sediments. The similar molecular composition of methyl ketones and cooccurring ethyl ketones containing one additional carbon atom indicates that the two classes are biosynthetically related.No source of these potential biological markers in lacustrine sediments has been identified. The abundance and unsaturation pattern of alkenones in lacustrine sediments may reflect the relative input and species composition, respectively, of algae presumed to belong to the Phylum Chrysophyta, by analogy with the marine source.     

Freshwater stromatolites with the cone-in-cone structure from the Neogene lacustrine sediments of Vietnam

Morphological features of the columnar-stratiform stromatolites, which resemble the cone-in-cone structure, from Neogene lacustrine sediments of northern Vietnam are analyzed. Their structural-textural peculiarities and interrelations with the host terrigenous sediments of a stromatolitic buildup are discussed. It is shown that stages of the growth of columns are recorded in the succession of vertically oriented carbonate plates, which form stromatolites, and in the serrate surface protrusions of the plates at their contacts with host sediments. It is established that replacement of the columnar stromatolites by the stratiform varieties in the section can be related to variations in the intensity of terrigenous material influx to the sedimentation basin. Stratiform stromatolites were formed during relatively slow accumulation of sedimentary material. Appearance of the columnar varieties is attributed to intensification of sedimentation.     

湖泊沉积物中重金属的环境地球化学

概要地回顾了近年来国内外湖泊沉积物中重金属环境污染方面的研究成果,介绍了湖相沉积物重金属研究的主要内容、方法和可能的发展方向.认为就重金属成因方面应加强区分其主要来源是岩石和矿物风化的碎屑产物、大气降尘、人类活动等的研究;重金属污染方面更应重视污染物质的生物有效性、迁移转化机理和重金属"二次污染"的研究;研究手段上,注重运用同位素示踪与定年技术来研究重金属的来源和污染历史,应用高分辨率沉积物钻心研究环境的变迁.最后提出加强多学科的综合研究,建立中国湖泊基准数据库,为探讨湖泊湿地的可持续发展提供依据.     

Distribution of n-alkanes in lacustrine sediments from subtropical lake in Brazil

The geochemical composition of lake bed sediments of a tropical reservoir in Brazil have been investigated. The C, N, P composition showed almost no variation between the different sampling points. All samples contained inorganic phosphorus (IP) ranging from 52 to 70%. The Redfield ratios show that the lake is without significant anthropogenic inputs. Most of the organic matter is composed by higher plants decomposition revealed in the total organic carbon (TOC):nitrogen (N) ratio ranging from 15.4 to 57.2. Also, TOC:organic phosphorus (OP) ranged from 265.3 to 933.6, suggesting that most of the organic matter has terrestrial origin from wood plants. The ratios suggest that most organic matter is influenced by the terrestrial characteristics of the watershed. Furthermore, the relative abundance of n-alkane homologues in the sediments was investigated. All samples have been analyzed for the n-alkanes C₈ to C₄₀. The sediments were dominated by n-alkanes C₂₅–C₃₈. It is concluded that n-alkane in sediments mainly come from terrestrial plants, however there is a contribution of submerged aquatic plants, especially in those sites in deeper areas of the lake. On the basis of P_aq index the n-alkanes in sediments comes from terrestrial plants, however there is a contribution from emerged/floating plants.The investigated lake seems to be considered as meso to eutrophic. Because of the relatively high primary productivity in the lakes, there is a substantial organic-matter flux to the sediments, which rapidly becomes anoxic. According to the pristine/phytane ratio the sediments represent an anoxic environment with values found between 0.38 and 1.72.     

咸化湖盆混积岩成因机理研究

关于海相及淡水湖盆混积岩的研究已相对完善,而针对咸化湖盆混积岩理论的形成及实践应用却鲜有报道,本文旨在系统地阐述咸化湖盆混积岩的成因机理、沉积模式、分布规律,对比其与一般混积岩沉积特征的异同点,并探讨其与油气富集特征的相关性。本文采用矿物学、微观岩石学分析方法进行混积岩矿物组成、沉积特征、储集空间类型研究,采取地质统计分析方法明确混积岩分布规律,并运用物性分析方法对比不同类型混积岩的储集性能。结合柴达木盆地西北区新近系混积岩研究实例,本文创新性地提出了欠补偿咸化湖盆的混积岩成因类型：机械成因的相混合混积岩和生物成因的藻混合混积岩。相混合又可划分为两种亚类：互层型混合、组构型混合;藻混合亦可划分为两种亚类：藻粘结混合、滑塌再混合。建立了咸化湖盆混积岩的沉积模式：混积岩主要发育于三角洲、水下扇、滩坝等碎屑岩沉积体系与湖相碳酸盐岩沉积体系的过渡相带以及藻灰岩发育区。明确了混积岩的分布规律,可归纳为“盆缘互层型、盆内组构型、藻混合局限分布”。混积岩沉积特征对比分析结果表明,任何环境下混积岩形成的先决条件均为碳酸盐岩的生长和聚集,而不同于淡水湖盆及海相混积岩沉积厚度大,生物含量高等特点,咸化湖盆混积岩单层厚度极薄,并发育特殊的藻混积岩类。综合研究认为,藻混合混积岩与油气储层的相关性要大于相混合混积岩。以上成果可为咸化湖盆混积岩,乃至陆相湖泊混合沉积物的成因类型及油气地质意义研究提供借鉴与参考。     

Long-chain alkenone distributions and temperature dependence in lacustrine surface sediments from China

Long-chain alkenones (LCK) of lacustrine surface sediments were analyzed in 37 lakes from China. The results obtained were complemented by published data from 13 other Chinese lakes. These lakes are located across large temperature and precipitation gradients, therefore allowing for an assessment of the distribution pattern of LCK and their temperature dependency. Different distribution patterns of LCK (C₃₇ predominant pattern and C₃₈ predominant pattern) were detected in the surface sediment samples. The ratio of C_37:4 methyl ketone to the sum of C₃₇ alkenones observed in the different lakes is highly variable (5%-96%, with mean value of 55%), and more than that seen in marine systems. The finding that some of the ocean LCK precursor algae (Gephyrocapsa oceanica, Coccolithus pelagicus) were also present in the limnic systems suggested that both systems might have similar biosynthetic sources. Empirical relationships between the alkenone unsaturation index U₃₇^k′ and different temperature sets (mean annual air temperature, mean annual air temperature in different seasons, and lake surface water temperature of July) were tested. The best correlation between U₃₇^k′ and temperature was obtained using mean annual air temperature. A general linear regression of U₃₇^k′ and MAAT can be expressed as U₃₇^k′ = 0.0328 × T + 0.126 (n = 38, r² = 0.83). Although questions such as species-uncertainty and other unknown factors for U₃₇^k′ temperature dependence still remain, the equation might be representative of the average contribution of LCK to sediments for these data over a wide range of surface temperatures, water chemistry and different alkenones-producer algal populations. The general relationship of U₃₇^k′ and mean annual air temperature is consistent with that in marine systems. It supports the suggestion that the biosynthetic pathway of alkenones and the mechanism of their temperature signal may be similar in both marine and limnic systems. LCK might be used as an important paleotemperature proxy in limnic environment.     

New Cretaceous Scoliidae (Vespida=Hymenoptera) from the Lower Cretaceous of Spain and Brazil

A new genus, Cretaproscolia, and three new species of scoliid wasps, Archaeoscolia hispanica, Cretoscolia montsecana and Cretaproscolia josai, are described from the Lower Cretaceous of Spain and Brazil. The species representing the new genus is attributed to the plesiomorphic extant subfamily Proscoliinae, while the two other new species are assigned to two previously described genera in the extinct, archaic subfamily Archaeoscoliinae. The Brazilian species is the first Mesozoic scoliidid to have been described from the New World.     

Magnetic stratigraphy of Lake Michigan sediments obtained from cores of lacustrine clay

Postglacial and lacustrine sediments from Lake Michigan have been paleomagnetically investigated. The primary goal was to test the feasibility of correlation between several cores in terms of their magnetic signatures. After alternating field and thermal demagnetizations, inclination and relative declination values were obtained that show characteristic short-term fluctuations. Major features, including changes in the magnetic intensity of the samples, correlate well in three of the longer cores, in good agreement with independent lithostratigraphic determinations. In addition, we have been able to detect local disconformities that appear as interruptions of the magnetic record. A continuous record of normal polarity has been found, extending from the present day to 13,000 ¹⁴C vears BP. No reversals were recorded, though at two stratigraphic levels shallow inclinations, together with declination swings and low intensities of magnetization, may indicate rapid geomagnetic excursions. The magnetic record was attained at the time of deposition or shortly thereafter, and can be used for a wide range of applications.     

Early Cretaceous fish trails from La Rioja, Spain

We report a new find of the fish trail Undichna unisulca in fluvial sediments of the Lower Cretaceous Oliván Group of the Cameros Basin (Aptian-Albian; Valtrujal, La Rioja, northern Spain). It is the second Mesozoic record of Undichna unisulca after the first discovery in the Lower Cretaceous of central Spain (Las Hoyas, Cuenca, central Spain). The trails are characterized by single sinusoidal waves which in this case are often surrounded by well-preserved lateral levees that rule out an undertrail hypothesis.The continental depositional setting, a floodplain fluvial system, reflects the known broad palaeoenvironmental distribution of Undichna and confirms its occurrences in freshwater settings.     

磷灰石对湖泊沉积物中水铁矿稳定性的制约

通过在滇池开展原位实验,研究探讨了湖泊沉积物中磷灰石制约水铁矿分解和转化的机制,以及二者共存时的环境效应。结果表明:将水铁矿放置到沉积物中1个月,矿物保持稳定;放置时间达到3个月时,添加磷灰石实验中水铁矿发生了显著物相转变。冬天(12—2月)实验中,转化产物随深度的变化趋势为针铁矿+磁(赤)铁矿→针铁矿+纤铁矿→针铁矿;夏天(6—9月)实验中,转化产物随深度的变化趋势为针铁矿+纤铁矿+磁(赤)铁矿→针铁矿+纤铁矿→未转化。透射电镜分析结果显示冬天实验中生成的磁性铁氧化物为纳米磁铁矿和磁赤铁矿,夏天实验中产生的则主要为纳米磁铁矿。X射线光电子能谱分析结果显示冬天表层实验样品具有较高P含量。分析表明的湖泊沉积物中磷灰石促进水铁矿转化的过程为:(1)微生物促进磷灰石溶解;(2)磷灰石溶解释放的P促进铁还原菌生长;(3)铁还原菌促进水铁矿还原;(4)水铁矿还原产生的溶解态Fe²⁺催化水铁矿向针铁矿、纤铁矿和磁铁矿转化。冬天及沉积氧化-还原界面最适宜磷灰石分解菌和铁还原菌生长,水铁矿的转化和P释放能力也更强,相应地内源磷释放的风险也更大。     

Preliminary magnetostratigraphic dating of Paleogene lacustrine sediments from the Shandong Province, East China

A detailed magnetostratigraphic and rock magnetic study was conducted on Tertiary lacustrine/fluvial sediments from Jiyang, Shandong, East China. High temperature susceptibility variation and thermal demagnetization show that magnetite is the main magnetic remanence carrier. The characteristic remanent magnetization (ChRM) was isolated above 150 °C by thermal demagnetization, and a detailed magnetic polarity sequence was established. The lacustrine/fluvial sediments were dated from polarity chron C18n.1r to polarity chron C15n, i.e., within the interval 39.631–34.655 Ma. The results of this study indicate the likelihood that either no hydrocarbon-bearing fluids were present after 34.655 Ma or, if there was any such fluid flow, the fluids must have gone through the section very quickly, without having any significant influence on the magnetic signal.     

Geochemistry of Miocene lacustrine sediments from the Sokolov Coal Basin (Czech Republic)

Sediments of the upper part of the Sokolov Formation of the Sokolov Brown Coal Basin consist mostly of brown lacustrine clays and claystones enriched in organic matter (2–18% TOC). The lower portion of the stratigraphic profile is formed mostly by kaolinite–illite clays and claystones, while the montmorillonite content increases in the upper portion. The change in the lithology of sediments is caused by the gradual erosion of the weathering crust in the source areas of the clastic material. Inversion of the weathering profile during erosion is manifested geochemically in a decrease in the Al₂O₃/Na₂O ratio and an increase in the SiO₂/Al₂O₃, Na₂O/K₂O and K₂O/TiO₂ ratios from the base to the top of the studied part of the Sokolov Formation. The amounts of trace elements (La, Ce, Nb, Zr, Cr, V, Sn) also decrease in the same direction. On the other hand, the amounts of Rb and Sr increase. The organic matter of the upper part of the Sokolov Formation consists primarily of Types I and II kerogen. Only near the base of the studied part of the formation, i.e., in the coal stringer, kerogen of Type III prevails. The extremely low degree of thermal maturity permits determination of the source of the organic matter and characterization of its accumulation environment. The organic material in the sediments is predominantly of algae origin. Relatively high amount of pentacyclic triterpanes of the hopane series indicates either the occurrence of cyanobacteria as primary producers or bacterial reworking during sedimentation and diagenesis. Organic matter accumulated under the conditions of a fresh-water lake or lake with slightly elevated salinity, in a dysoxic aqueous environment. The alternation of organic carbon-rich layers with layers low in organic matter is explained in terms of changes in the degree of dysoxia of the aqueous environment and a variation in the intensity of oxidation and mineralization of the organic material.     

Molecular taphonomy of macrofossils from the Cretaceous Las Hoyas Formation,Spain

Macromolecular analysis of fossil fish scales from the Cretaceous Las Hoyas Formation (using pyrolysis-gas chromatography-mass spectrometry) revealed a dominant aliphatic composition (C₈ to C₂₂) whereas modern fish scale is proteinaceous (largely collagenous). Structural analysis of the aliphatic polymer using thermochemolysis revealed the importance of ester linkages; saturated fatty acids C₁₄ to C₁₈ (particularly C₁₆) are the most abundant. These acid components and their unsaturated counterparts are evident in the lipid composition of modern fish scales. Thus, the aliphatic composition of the fossil scales is probably a result of the incorporation of lipids (including a C₁₉ aromatic hydrocarbon) from the original indicating preservation by in situ polymerization of labile aliphatic components. Fossil arthropods and plants from the same deposit also show a dominant aliphatic macromolecular component, likely derived predominantly by crosslinking of free lipid precursors. Differences in the relative distribution of molecular components indicate likely chemosystematic differences between different fossil groups.     

Heavy metals and metalloids in sediments from the Llobregat basin,Spain

The concentration of heavy metals and metalloids (As, Cd, Cr, Cu, Hg, Ni, Pb, Sb and Zn) in sediments from the River Llobregat and its tributaries (Anoia and Cardener) was studied. Samples collected at 17 locations during four different periods were analysed by ICP-MS. The heavy metal enrichment at some sites along the rivers reflects the effects of agricultural activities, sewage treatment plant effluents, collectors' discharges and industrial activities. Principal component analysis (PCA) was used to describe trends in contamination and to find groupings among the investigated areas. The Llobregat and Cardener sediments appeared to have features of an unpolluted river, even though significant amounts of domestic and industrial wastewater are discharged into these rivers. On the other hand, the sediments from the River Anoia showed high Cr and Hg levels originating from industrial activities. The concentrations of Cr and Hg ranged from 91–540 and 0.28–2.29 µg/g respectively.