华北地区Lg尾波衰减研究--Lg尾波Q的测量

利用1989～1998年间发生在中国华北地区ML≥3.0级的地震事件,华北遥测台网以及数字化台网记录到的信噪比较高的Lg尾波时间序列,经过滤波、消除背景噪声等预处理,采用单台记录叠加频谱比法,得到传播路径上Lg尾波Q0（Q=Q0fη, Q0是1Hz的Q值,η是Q值与频率相关系数）,进而获得该地区Q0和η的空间分布. 测量结果表明,华北地区地壳Lg尾波Q0值分布存在显著的横向不均匀性,这种不均匀性与该地区地壳的速度分布基本一致,表现为与该地区地表地质特征明显的一致性,即传播路径位于太行山隆起和燕山隆起区为高Q0值分布;传播路径位于冀中坳陷和黄骅坳陷等平原区表现为低Q0值;传播路径位于隆起区和坳陷区二者之间,其Q0值也介于二者之间,说明华北地区的地壳结构没有很大的阶跃式变化而使波导遭到破坏,Lg尾波Q0值基本上反映了地壳内介质滞弹性的固有衰减.     

福建河田高分异花岗岩的矿物和全岩地球化学找矿标志研究

我国的华南地区是一个钨、锡、钼、铋、铀、铌钽、铅锌、稀有、稀土多金属成矿区。近年来,高精度年代学数据表明上述矿产集中爆发形成于晚侏罗世的165~150Ma。野外和实验证据表明,花岗岩可以划分为高分异花岗岩、低分异花岗岩和未分异花岗岩。从目前的研究结果来看,钨、锡、铌钽、锂、铍等成矿作用都与高分异花岗岩密切相关。建立与这些矿产有关高分异花岗岩的普适性的矿物学、矿物地球化学和全岩地球化学的指标,有助于判断植被覆盖严重和风化严重地区、数据积累较少的岩体的成矿潜力。位于福建省长汀县境内的河田花岗岩体新鲜露头少,大部分岩体都掩盖在厚厚的风化层下,且植被覆盖严重,但是该岩体中已发现多处锡、钨、铅锌矿(化)点。本研究发现,该岩体的锆石U-Pb年龄、石榴子石和全岩地球化学特征与江西西华山第二期成矿花岗岩具有高度相似性,因此推断河田岩体可能具有成钨锡多金属(超)大型矿的成矿潜力。此外,当花岗岩向高分异阶段不断演化的过程中,某些元素比值(例如Rb/Sr、Zr/Hf和Nb/Ta)可以作为衡量岩浆的结晶分异程度的参数;西华山和河田花岗岩在达到熔体-流体相互作用阶段时,全岩Zr含量和Zr/Hf比值大概在Zr=50×10-6和Zr/Hf=15处发生转折。同时,与不成矿花岗岩中的石榴子石相比,成矿花岗岩中石榴子石的Sn、Y和Yb元素含量明显升高,可达2~10倍,因此,高分异花岗岩的石榴子石的微量元素特征可能是重要的找矿标志之一。     

Sedimentation Patterns of Photosynthetic Bacteria Based on Pigment Markers in Meromictic Lake La Cruz (Spain): Paleolimnological Implications

Sedimentation fluxes of photosynthetic pigments and their derivatives, focused on the anoxygenic bacteria populations, were determined in meromictic Lake La Cruz over a three-year period using sediment traps. Bacterial settling occurs in pulses in response to lake dynamics. Two main annual events affect particle settling in Lake La Cruz: (1) Following an event of massive calcium precipitation in summer that caused water whiting, a maximum flux of chlorophyll a and derivatives towards the sediment was registered. Although whiting is accompanied by massive phytoplankton biomass sinking, it was not followed by concomitant photosynthetic bacterial sinking. (2) In contrast, the disruption of the chemocline and the contact of bacterial populations with oxygenated waters during autumn overturn provoked a destruction of the sulfur bacterial plate, causing mass mortality, registered in the settling material as photosynthetic pigments and their derivatives from phototrophic bacteria. Among the bacteriochlorophyll a oxidation products, bacterioviridin (bvir) was detected in high relative abundance in the settled material collected by sediment traps. The much increased flux of bvir after thermal overturn, associated with mass mortality of the purple sulfur bacterium, Amoebobacter purpureus, confirms the suitability of this molecule as a useful paleoindicator of the degree of oxygen exposure experienced by the purple sulfur bacteria population.     

Using gemorphological markers to discriminate Neogene tectonic activity in the Precordillera of North Chilean forearc (24–25°S)

We study the Neogene tectonic activity in a sector of the Precordillera in the Andean forearc analysing aerial photographs, satellite images and fieldwork data. The interpretation of alluvial landforms, drainage organisation and evolution of intermittent river networks affecting post-Lower Miocene deposits allow us to recognize low intensity tectonic processes controlling the landscape evolution. All these geomorphological markers indicate no strike-slip offsets, but repeated and small tectonic pulses that reactivate previous structures originated under a transpressive context. The observed deformation pattern is the consequence of E–W orthogonal compression resulting in limited shortening, related to the accommodation of deformation in the Chilean forearc of the Neogene uplift of the Altiplano-Puna.     

Comparative study by infrared spectroscopy of the organic matter of phosphate-rich (Oulad Abdoun basin) and black shale (Timahdit basin) series (Morocco)

Fourier transform infrared spectroscopy has been used to get quantitative information on the oxidation state of the organic matter of stable residues extracted from strata of the phosphate-rich basin of Oulad Abdoun and from oil shales of the Timahdit basin, Morocco.Throughout the respective filling of both basins the redox conditions have been more oxidizing in the top part of the sediments in Oulad Abdoun basin than in the Timahdit basin. This is interpreted as the result of the sedictural evolution of the basin Oulad Abdoun basin having evolved in stable platform conditions while the Timahdit basin evolved in subsiding ones.The phosphate-rich beds contain the more oxidized organic stable residues. Sedimentological evidence shows that the oxidation was associated reworking processes. These processes are responsible for the progressive concentration of the phosphatic grains and prove to be necessary for the P₂O₅ content to become higher than 10% this value being the highest encountered in the sediment within which the phosphatic grains form.     

Identification of bicyclic terpenoid hydrocarbons in the saturate fraction of Athabasca oil sand bitumen

The bicyclic terpanes reported to be present in numerous petroleums have been detected in the saturate fraction of the Athabasca oil sand bitumen. This series of compounds has been found to extend from C₁₅ to at least C₂₄ and their structures have been established by means of comparisons with synthetic C₁₈ and C₂₀ samples of known stereochemistry.     

Lipids of aquatic organisms as potential contributors to lacustrine sediments—II

The relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments, previously examined for n-alkanols and steroids, is now reported for hydrocarbons, ketones and carboxylic acids.The n-C₇ alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment. Bacterial biomarkers, including hopenes and fatty acids, were detected in the photosynthetic bacterial layer occurring just above the sediment-water interface.Within the sediment the apparent conversion of free n-alkanes, alkan-2-ones and ω-hydroxy acids to the corresponding bound form is noted; microbiological oxidation of n-alkanes to alkan-2-ones is supported by the detection of the intermediate alkan-2-ols with a distribution similar to that of the ketones. The geochemistry of sediment deposited c. 1900, prior to biological study of the site, was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition. A qualitative difference in algal input to the older sediment is inferred from the low Δ⁷-sterol content and presence of 2,6,10-trimethyl-7-(3-methylbutyl)-dodecane. However, there was still significant dinoflagellate input, as indicated by the presence of 4α-methylsterols. A difference in higher-plant input to the older sediment, indicated from the n-alkane, alkene and triterpenoid ketone distributions, is consistent with the recent development of tree cover.     

Transport and fate of Danube Delta terrestrial organic matter in the Northwest Black Sea mixing zone

Within the framework of the European project EROS 21, a biogeochemical study of particles transported from the Danube Delta to the Northwestern Black Sea whose carbon cycle is dominated by riverine inputs was carried out in spring off the Sulina branch of the Danube Delta. The distribution of particulate organic carbon (POC), chlorophyll a (Chl a), C/N, and δ¹³C evidenced an omnipresent contribution of terrestrial organic matter throughout the study area together with a dilution of these inputs by freshwater and marine organisms. Four lipid series, n-alkanoic acids, n-alkanes, n-alkanols, and sterols were analyzed by gas chromatography and gas chromatography/mass spectrometry. Several signature compounds were selected to delineate dispersion of terrestrial organic carbon: (1) long-chain n-alkanoic acids in the range C₂₄–C₃₄, long-chain n-alkanes in the range C₂₅–C₃₅, long-chain n-alkanols in the range C₂₂–C₃₀, 24-ethylcholesta-5,22-dien-3β-ol (29Δ^5,22) and 24-ethylcholesterol (29Δ⁵) for vascular plant-derived material and (2) coprostanol (27Δ^0,5β) for faecal contamination associated with sewage effluents. A marked decrease was observed between the concentrations of different vascular plant markers characterizing the two end members: riverine at salinity 0.3 and marine at salinity 15.5. The decrease observed for marine/riverine end members (expressed as a function of organic carbon) varied in a large range, from 4% for n-alkanes to 18.6%, 20.4% and 24% for n-fatty acids, n-alkanols and sterols, respectively. These values reflect a combination of various processes: size-selective particle sedimentation, resuspension of different particle pools of different sizes and ages, and/or selective biological utilization. The multi-marker approach also suggested the liberation in the mixing zone of terrestrial moieties, tightly trapped in macromolecular structures of the riverine material. The greatest decrease for marine/riverine end members was observed for coprostanol (0.9%), underlining the efficiency of the mixing zone as a sink for sewage-derived carbon.