Carbon and oxygen isotopic composition of car- bonate cements of different phases in terrigenous siliciclastic reservoirs and significance for their origin： A case study from sandstones of the Triassic Yanchang Formation, southwestern Ordos Basin, China

Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope （their δ^18O values range from -0.3‰- -0.1‰） and lighter oxygen isotope （their δ^18O values range from -22.1‰- -19.5‰）. Generally, they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water. This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones, preserving intragranular volume and providing the mass basis for later disso- lution caused by acidic fluid flow to produce secondary porosity. Ferriferous calcites are characterized by relatively light carbon isotope with δ^13C values ranging from -8.02‰ to -3.23‰, and lighter oxygen isotope with δ^18O values ranging from -22.9‰ to -19.7‰, which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis. As the mid-late diagenetic products, ferriferous cal- cites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir. The late ankerite is relatively heavy in carbon isotope with δ^13C values ranging from -1.92‰ to -0.84‰, and shows a wide range of variations in oxygen isotopic composition, with δ^18O values ranging from -20.5‰ to -12.6‰. They are believed to have nothing to do with decarboxylation, but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation, and the alkaline diagenetic environment at the mid-late stage would promote this process.     

内蒙古兴安盟杜尔基岩体特征研究

内蒙古兴安盟杜尔基岩体位于大兴安岭中南段,岩性主要为中—细粒二长花岗（斑）岩、中—粗粒二长花岗岩、细粒二长花岗岩。岩石化学分析结果属于碱性岩系列,具有高硅、高钾、富碱、过铝、贫铁、镁、钙特征。稀土元素总量平均值为112．43μg／g,球粒陨石标准化曲线整体平缓右倾,具有Eu负异常;微量元素蛛网图解表现为“W”型形态．具有明显的Sr、Ba、Ti负异常,反映了强烈的分离结晶作用存在。4个样品K-Ar全岩法测年结果为100．15-120．29Ma,说明岩体形成于早白垩世。反映杜尔基地区在早自垩世可能处于相对稳定的拉张环境。     

Geochemical Eccentricity of Ground Water Allied to Weathering of Basalts from the Deccan Volcanic Province,India: Insinuation on CO<Subscript>2</Subscript> Consumption

Analyses of 72 samples from Upper Panjhara basin in the northern part of Deccan Plateau, India, indicate that geochemical incongruity of groundwater is largely a function of mineral composition of the basaltic lithology. Higher proportion of alkaline earth elements to total cations and HCO₃>Cl + SO₄ reflect weathering of primary silicates as chief source of ions. Inputs of Cl, SO₄, and NO₃ are related to rainfall and localized anthropogenic factors. Groundwater from recharge area representing Ca + Mg–HCO₃ type progressively evolves to Ca + Na–HCO₃ and Na–Ca–HCO₃ class along flow direction replicates the role of cation exchange and precipitation processes. While the post-monsoon chemistry is controlled by silicate mineral dissolution + cation exchange reactions, pre-monsoon variability is attributable chiefly to precipitation reactions + anthropogenic factors. Positive correlations between Mg vs HCO₃ and Ca + Mg vs HCO₃ supports selective dissolution of olivine and pyroxene as dominant process in post-monsoon followed by dissolution of plagioclase feldspar and secondary carbonates. The pre-monsoon data however, points toward the dissolution of plagioclase and precipitation of CaCO₃ supported by improved correlation coefficients between Na + Ca vs HCO₃ and negative correlation of Ca vs HCO₃, respectively. It is proposed that the eccentricity in the composition of groundwater from the Panjhara basin is a function of selective dissolution of olivine > pyroxene followed by plagioclase feldspar. The data suggest siallitization (L < R and R _k) as dominant mechanism of chemical weathering of basalts, stimulating monosiallitic (kaolinite) and bisiallitic (montmorillonite) products. The chemical denudation rates for Panjhara basin worked out separately for the ground and surface water component range from 6.98 to 36.65 tons/km²/yr, respectively. The values of the CO₂ consumption rates range between 0.18 × 10⁶ mol//km²/yr (groundwater) and 0.9 × 10⁶ mol/km²/yr (surface water), which indicates that the groundwater forms a considerable fraction of CO₂ consumption, an inference, that is, not taken into contemplation in most of the studies.     

甘肃庆城庄19井区上三叠统延长组长82亚油层组 低渗透储层的地质特征

长82亚油层组是甘肃庆城地区庄19井区上三叠统延长组中储集砂岩相对富集的层位,但砂岩低渗透性的特点显著,成为影响该区石油储产量增长的主要地质因素.结合前人的相关工作,通过钻井岩心观察、测井曲线分析、储层岩石实验测试等工作,详细地分析了庄19井区长82亚油层组低渗透储层的地质特征,认为沉积微相和压实作用、胶结作用是控制低渗透性储集砂岩发育和分布的主要地质因素,寻找以水下分流河道微相为代表的有利储集相带砂岩体是油气勘探的重要方向.     

(ϖμ/ϖT) P of the lower mantle

We estimate (/T) _P of the lower mantle at seismic frequencies using two distinct approaches by combining ambient laboratory measurements on lower mantle minerals with seismic data. In the first approach, an upper bound is estimated for |(/T) _P | by comparing the shear modulus () profile of PREM with laboratory room-temperature data of extrapolated to high pressures. The second approach employs a seismic tomography constraint ( lnV _S / lnV _P ) _P =1.8–2, which directly relates (/T) _P with (K _S /T) _P . An average (K _S /T) _P can be obtained by comparing the well-established room-temperature compression data for lower mantle minerals with theK _S profile of PREM along several possible adiabats. Both (K _S /T) and (/T) depend on silicon content [or (Mg+Fe)/Sil of the model. For various compositions, the two approaches predict rather distinct (/T) _P vs. (K _S /T) _P curves, which intersect at a composition similar to pyrolite with (/T) _P =–0.02 to –0.035 and (K _S /T) _P =–0.015 to –0.020 GPa/K. The pure perovskite model, on the other hand, yields grossly inconsistent results using the two approaches. We conclude that both vertical and lateral variations in seismic velocities are consistent with variation due to pressure, temperature, and phase transformations of a uniform composition. Additional physical properties of a pyrolite lower mantle are further predicted. Lateral temperature variations are predicted to be about 100–250 K, and the ratio of ( lnp/ lnV _S ) _P around 0.13 and 0.26. All of these parameters increase slightly with depth if the ratio of ( lnV _S / lnV _P ) _P remains constant throughout the lower mantle. These predicted values are in excellent agreement with geodynamic analyses, in which the ratios ( ln / lnV _S ) _P and ( / lnV _S ) _P are free parameters arbitrarily adjusted to fit the tomography and geoid data.     

内蒙古正镶白旗碎斑熔岩岩石学特征及其岩相划分

白旗碎斑熔岩为不规则穹状体,可分为边缘玻质碎斑熔岩、过渡霏细碎斑熔岩、中心粒状碎斑熔岩和根部花岗斑岩四个岩性带。从玻质碎斑熔岩到粒状碎斑熔岩,斑晶碎裂度逐渐减弱,珠边结构在粒状碎斑熔岩中最发育,根部花岗斑岩与正常次火山岩相近。碎斑熔岩中钾长石有序度低,指示了岩石高温成因特征。白旌碎斑熔岩属太平洋岩系钙碱质系列,原始岩浆由来源于上地幔和下地壳熔体的混熔作用形成。     

High-resolution sedimentary record of lead in the coastal mud of the East China Sea in the past one hundred and fifty years

In the East China Sea （ECS）, there are some mud areas, including the south coastal mud area, the north coastal mud area, and the mud area to the southwest of Cheju Island. X-ray fluorescence （XRF） techniques and Thermal Ionization Mass Spectrometry （TIMS） were used to study the high-resolution sedimentary record of Pb concentrations and Pb stable isotopic compositions in the past one hundred and fifty years in the coastal mud of the ECS. Pb concentrations of a ^210Pb dating S5 core in the study area have increased rapidly since 1980, and reached the maximal value with 65.08 μg/g in 2000, corresponding to the fast economic development of China since the implementation of the ＂Reform and Open Policy＂ in 1978; ^206Pb/^207Pb ratios generally had stabilized at 1.195 from 1860 to 1966, and decreased gradually from 1966 to 2000, indicating that the anthropogenic source Pb contribution to the ECS has increased gradually since 1966, especially since 1980. Pb concentrations decreased distinctly from 2000 to 2003 and ^206Pb/^207Pb ratios increased from 2001 to 2003, corresponding closely to the ban of lead gasoline from 2000 in China. From 1950 to 2003, there occurred four distinct decrease events of ^206Pb/^207Pb, possibly responding to the Changjiang River （Yangtze River） catastrophic floods in 1998, 1991, 1981 and 1954; from 1860 to 1966, there were two decrease periods of ^206Pb/^207Pb, which may respond to the catastrophic floods of Changjiang River in 1931 and 1935, and 1870. As a result of the erosion and drowning by the catastrophic floods, the anthropogenic lead accumulated in soil and water environments over a long period of time was brought into the Changjiang River, then part of them was finally transported into the ECS, which leads to changes in Pb stable isotopic composition.     

Reference Materials in Geoanalytical Research -Review for 2004 and 2005

This review gives an overview of the use and development of reference materials of geochemical and environmental interest in the literature of the years 2004 and 2005. In these years the performance of existing methods has been improved and new geochemical applications using new techniques have been developed. Accordingly, there was an increasing need for new reference materials, especially for in situ microanalysis and for precise stable isotope measurements. In addition, there was a notable trend for further characterisation of existing reference materials, mainly for the platinum-group elements. This review focuses on five topics: reference materials for platinum-group elements, reference glasses for in situ microanalysis, zircon reference materials, isotopic reference materials, and the development and certification of reference materials.     

Secular variations of the upper crust composition: Implication of geochemical data on the Upper Precambrian shales from the Southern Urals western flank and Uchur-Maya region

In the mid-1980s, it was concluded based on geochemical study that Th, Sc, La concentrations and ratios Th/Sc, La/Sc and Eu/Eu* did not wary significantly in the post-Archean time. It was impossible to judge about compositional variations of upper crust during the Riphean and Vendian, because data of that time characterized a limited number of samples from the post-Archean basins of Australia, New Zealand, and Antarctic. Considered in this work are variations of Eu/Eu*, LREE/HREE, Th/Sc, and La/Sc ratios in Upper Precambrian fine-grained siliciclastic rock of the Southern Urals western flank (Bashkirian meganticlinorium) and Uchur-Maya region (Uchur-Maya plate and Yudoma-Maya belt). As is established, only the Eu anomaly in the studied siliciclastic rocks is practically identical to this parameter of the average post-Archean shale. Three other parameters plot on the Riphean-Vendian variation curves with positive and negative excursions of diverse magnitude, which do not coincide always in time. It is assumed that these excursions likely mark stages of local geodynamic activity, destruction of pre-Riphean cratons, and progressing recycling of sedimentary material during the Riphean.