Benthic nutrient fluxes in the intertidal flat within the Changjiang （Yangtze River） Estuary

In an annual cycle from March 2005 to February 2006, benthic nutrient fluxes were measured monthly in the Dongtan intertidal flat within the Changjiang （Yangtze River） Estuary. Except for NH4^＋, there always showed high fluxes from overlying water into sediment for other four nutrients. Sediments in the high and middle marshes, covered with halophyte and consisting of macrofauna, demonstrated more capabilities of assimilating nutrients from overlying water than the low marsh. Sampling seasons and nutrient concentrations in the overlying water could both exert significant effects on these fluxes. Additionally, according to the model provided by previous study, denitrification rates, that utilizing NO3- transported from overlying water （Dw） in Dongtan sediments, were estimated to be from -16 to 193 μmol·h^-1·m^-2 with an average value of 63 μmol·h^-1·m^-2 （n=18）. These estimated values are still underestimates of the in-situ rates owing to the lack of consideration of DN, i.e., denitrification supported by the local NO3^- production via nitrification.     

底摩擦重力试验在倾倒变形岩体稳定性研究中的应用

底摩擦重力试验(底摩擦试验)是利用相似理论分析原理,将研究原形按几何比例和各种物理力学参数,制作相似模型及确定相应的边界条件。然后按照相似边界条件进行加载试验,再现曾经发生过或今后将会出现的物理力学现象,进而了解其发展演化规律及其对工程的影响。澜沧江某水电站坝肩主要为典型的倾倒变形岩体,为探讨倾倒变形岩体在天然重力场条件的变形破裂发展趋势。试验采用模拟重力场条件的岩体底摩擦模型试验技术模拟分析岩体倾倒变形进一步发展演变过程及特征。     

封闭体系有机质与有机碳氢氮恢复动力学研究

在封闭体系的条件下,对典型的Ⅰ、Ⅱ、Ⅲ型干酪根在热演化过程中的损失进行生烃动力学研究,获得了Ⅰ、Ⅱ、Ⅲ型干酪根的总量、有机碳、氢以及氮质量损失动力学参数。用Kinetics软件计算了封闭体系干酪根有机碳丰度、氢碳原子比和氮碳原子比的恢复系数。认为在对高成熟—过成熟干酪根进行生烃评价时,Ⅰ、Ⅲ型干酪根残余有机碳丰度需要进行恢复,而Ⅱ型干酪根残余有机碳丰度不需要恢复。三种类型干酪根的氢碳原子比均需要进行恢复。     

辽东湾凝析气田超压成因及侧向传递机制初探

位于辽东湾西部低凸起北端的JZ20-2超压凝析气田,离供烃中心较远,压力系数却达到1.56~1.7,这在我国东部裂谷盆地比较少见。经过综合分析,作者认为JZ20-2凝析气田异常高压的形成与其所处的特殊地质背景紧密相关,辽中凹陷沙河街组三段超压凝析油气沿不整合面、砂体输导通道向辽东湾西部低凸起的运移、充注和能量的侧向传递是JZ20-2凝析气田异常高压形成的根本原因,而上覆东营组二段下亚段-东营组三段巨厚的强超压泥岩封盖和辽西3号边界断层侧向遮挡共同构成的优越封闭环境是超压保存的必要条件。本文分析了该气田超压特征及其远距离超压侧向传递的成因机制,不仅有助于揭示辽东湾西部低凸起超压流体运移聚集的规律和成藏作用,而且可能提供了一个超压远距离侧向传递的典型实例。     

Wenchuan Earthquake： Way of thinking is changed

On 12 May, 2008, at 14：28：04 local time, an Ms 8.0 earthquake struck the Wenchuan County, Sichuan Province, in southwest China （Figure 1）. This quake left about 70,000 people dead, 18,000 missing and over 370,000 injured. In the 75 days after the main shock, 20,000 aftershocks were recorded, which included 241 with Ms≥4.0, 205 with 4.0≤M≤4.9, 30 with 5.0≤Ms≤5.9, and 6 with Ms≥6.0. The largest aftershock took place 13 days after the main shock, in Qingchuan County, 110 km northeast of the epicenter of the quake （Chen, 2008）. The losses from the quaketriggered geological disasters accounted for over a third of the total quake losses, which is extremely rare in the history of earthquake disasters. Secondary disasters, such as landslides, rockslides, landfalls, debris flows, etc., were widely distributed. Large numbers of buildings collapsed, including ones with steel reinforcing in the area of the epicenter. Infrastructure was badly damaged. In many areas, communications, and power and water supplies were cut off. The earthquake left over 35 large quake-dammed lakes, which threatened further disasters in the catchment areas.     

Modeling of water–rock interactions in an aquitard of sandy clay in the coastal area near Beihai,China

Unconsolidated sand, gravel and clay deposits near Beihai and in the Leizhou Peninsula in southern China form an unconfined aquifer, aquitard and a confined aquifer. Water and soil samples were collected from the two aquifers in the coastal Beihai area for the determination of chemical compositions, minerals and soluble ions. Hydrogeochemical modeling of three flow paths through the aquitard are carried out using PHREEQC to determine water–rock interactions along the flow paths. The results indicate that the dissolution of anorthite, fluorite, halite, rhodochrosite and CO₂, and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the unconfined aquifer to the confined aquifer. Cation exchanges between Na and Ca can also happen along the flow paths.     

Distribution of the C37 tetra-unsaturated alkenone in Lake Qinghai, China: A potential lake salinity indicator

The alkenone unsaturation index U^K′₃₇ has been applied to reconstruct past temperature changes in both marine and lacustrine systems. However, few studies have addressed whether the relative abundance of the C_37:4 alkenone to the total C₃₇ production (%C_37:4) can reflect surface salinity changes in lacustrine systems. Here we present long-chain C₃₇ alkenone distribution patterns in surface sediments from Lake Qinghai, China. Surface sediments were sampled over a large range of surface salinity changes (1.7-25 g/l) within Lake Qinghai and its surrounding lakes, while temperature differences at these sampling locations should be relatively small. We have found that %C_37:4 varies from 15% to 49% as surface salinity decreases. We tentatively describe this %C_37:4-salinity link with a general linear regression: %C_37:4 = 53.4 (±7.8) − 1.73 (±0.45) × S (n = 28, r² = 0.62), although step-wise %C_37:4 changes in response to salinity variation may exist. U^K′₃₇ values vary between 0.10 and 0.16 at these sites and the inferred range of lake water temperature changes is ∼2-3 °C, suggesting that U^K′₃₇ largely reflects temperature signal across a large salinity range, consistent with previous findings that U^K′₃₇ can indicate temperature changes over a large diversity of environmental settings. We have also found that U^K′₃₇ values are correlated with salinity changes (r² = 0.4), and thus cannot exclude potential temperature effect on %C_37:4 and salinity effect on U^K′₃₇ in this study. However, even extreme estimates of temperature differences within the lake are still unable to explain the observed %C_37:4 changes. We therefore suggest that %C_37:4 could be used to infer past lake salinity changes at a regional scale.     

Cr-spinel/olivine and Cr-spinel/liquid nickel partition coefficients from natural samples

The Nernst partition coefficient of nickel (D^Ni) between Cr-spinel and silicate melt in natural systems has been investigated using mid-ocean ridge basalts (MORB) and other volcanic rocks. The Cr-spinel/olivine D^Ni values in volcanic rocks are between 1.2 and 0.3, indicating that the Cr-spinel/liquid D^Ni values vary from slightly higher to significantly lower than the olivine/liquid D^Ni values in natural systems. The Cr-spinel/liquid D^Ni values from the MORB samples vary between 6 and 11, slightly higher than those from the S-bearing experiments of Satari et al. [Satari P., Brenan J. M., Horn I. and McDonough W. F. (2002) Experimental constraints on the sulfide- and chromite-silicate melt partitioning behavior of rhenium and platinum-group elements. Economic Geology97, 385-398]. The results of the MORB samples and the experiments of Satari et al. (2002) indicate a negative correlation between the Cr-spinel/liquid D^Ni and the X_Cr values in Cr-spinels (Cr cation number on the basis of 3 total cations in the spinel structure). Variations of Cr-spinel/liquid D^Ni values with Cr-spinel compositions can be estimated from an empirical equation based on the results of the MORB samples and the experiments by Satari et al. (2002). The choice of Cr-spinel/liquid D^Ni = 10 for numerical modeling by Righter et al. [Righter K., Leeman W. P. and Hervig R. L. (2006) Partitioning of Ni, Co, and V between spinel-structured oxides and silicate melts: importance of spinel composition. Chemical Geology227, 1-25] is reasonable for basaltic systems. For picritic and komatiitic systems a lower value of ∼5 is more appropriate.     

Hydrogeochemical characteristics of central Jianghan Plain, China

The central Jianghan Plain is the semi-closed basin in the middle reaches of Yangtze River. A total of 78 water samples targeting groundwater were collected from 75 sites in this study site, the area between Yangtze River and Han River, including rivers and lakes for temperature, pH, electrical conductivity (EC), total dissolved solids (TDS) and ion composition measurements. Correlation matrix was used to assess the geochemical and anthropogenic processes. The most confined groundwater was grouped into HCO₃–Ca–Mg, while phreatic groundwater and surface water had a more diversified hydrochemistry. The spatial variation in overall water quality as well as comparison with WHO (World Health Organization) standards for drinking water is illustrated. Mn, As and NO₃ ^? concentrations were found to exceed the allowable limits for drinking water of WHO guidelines, and they also show remarkable spatial variations. Abnormally high nitrate concentration, up to 150–190 mg/l, was found only in phreatic groundwater, which suggested that the nitrate pollution might be caused by agricultural activities. The present study may be helpful in further studies concerning water quality issues in this area where groundwater is a vital source for drinking and other activities.     

新疆阿尔泰塔拉特铁铅锌矿床流体包裹体研究及矿床成因

塔拉特铁铅锌矿位于新疆阿尔泰造山带南缘的阿巴宫多金属成矿带,矿体赋存于克兰盆地下泥盆统康布铁堡组中,为一套海相中酸性火山岩-火山碎屑岩、陆源碎屑沉积岩-碳酸盐岩建造,脉状矿体受阿巴宫大断裂次级断裂控制.根据矿物组合和脉体穿插关系,塔拉特铁铅锌矿可分为4个成矿阶段:矽卡岩,氧化物,硫化物和碳酸盐阶段,后3个阶段均有石英共生.其中,硫化物(方铅矿-闪锌矿±磁黄铁矿±黄铜矿)阶段是铅锌成矿的主要阶段.不同阶段石英中广泛发育流体包裹体,可分为水溶液包裹体(W型)、纯CO2包裹体(PC型)、CO2-NaCl-H2O包裹体(C型)及含子矿物多相包裹体(S型)4类.冷热台显微测温和激光拉曼分析表明,氧化物阶段石英含有4种类型的包裹体,以W型为主,C型和S型包裹体次之,包裹体均一温度介于271～ 426℃,W型和C型盐度范围0.5％～22.4％ NaCleqv,S型包裹体盐度30.5％ ～40.6％ NaCleqv;硫化物阶段的石英流体包裹体为W型、C型和PC型,均一温度为204 ～ 269℃,盐度介于0.2％～15.6％ NaCleqv之间;碳酸盐阶段的矿物只含W型包裹体,均一温度集中在175～211℃之间,盐度为1.1％ ～9.9％ NaCleqv.利用C型包裹体对硫化物阶段成矿压力估算,得到107 ～ 171MPa,对应深度为4～6km.塔拉特铁铅锌矿初始成矿流体具有高温、高盐度、富CO2的特征,但碳酸盐阶段低盐度、贫CO2,流体不混溶和混合作用导致了成矿物质的沉淀.塔拉特铁铅锌矿的地质和成矿流体特征显示其为碰撞造山体制形成的矽卡岩型成矿系统.