Hydrodynamic characterization of a Sahelian coastal aquifer using the ocean tide effect (Dridrate Aquifer,Morocco)

Abstract

In wells tapping coastal aquifers, piezometric fluctuations can be observed in response to the ocean tide. Simultaneous recordings of the ocean tide and of the piezometric variations may provide a basis for characterizing the hydrodynamics of the aquifer. This approach was attempted to characterize the Dridrate aquifer, located on the Atlantic coast of Morocco. This aquifer accounts for most of the regional drinking water resources. However, its hydrodynamic characteristics are very poorly known. The study compares observed and simulated piezometric fluctuations, under various assumptions (confined, semi-confined aquifer). The model, which best explains the hydrodynamic behaviour of this aquifer is a semi-confined and strongly heterogeneous aquifer model (calculated hydraulic diffusivity values vary over several orders of magnitude). This result is new and rather surprising, since to date this aquifer was considered confined in view of its geological setting. Consequently, new questions are raised regarding the protection and management of the groundwater resources of this aquifer.     

云南德钦鲁春铜铅锌矿床硫铅氢氧同位素特征及地质意义

鲁春铜铅锌矿床位于中咱-中甸板块和昌都-思茅板块之间的金沙江构造带中部,矿体长约3 km,厚度在1.06～16.35 m之间。其赋矿围岩为火山沉积岩系,容矿构造为印支期逆断层。鲁春铜铅锌矿床矿石中硫化物的δ34S值变化于3.5‰～6.8‰之间,硫化物的206Pb/204Pb比值为18.554～18.656,207Pb/204Pb比值为15.662～15.752,208Pb/204Pb比值为38.801～39.009。石英流体包裹体的HO182δO值变化范围为2.74‰～1.25‰,δDV-SMOW变化范围为107‰～123‰。鲁春铜铅锌矿床的硫铅氢氧同位素分析结果表明,该矿床成矿物质来源于地幔,部分来源于岩浆,在成矿流体上升过程中,有壳源物质的加入。早二叠世晚期金沙江洋盆向西俯冲形成了一系列逆断层,同时导致下地壳部分熔融,引发大规模的火山岩浆作用。在晚三叠世早期,构造背景由挤压环境到伸展环境的转折期,这些逆断层具有张性的特点,为后期的成矿热液提供了有利的容矿构造。上升的岩浆为地幔楔内的成矿流体提供了通道。岩浆内的部分成矿流体进入白茫雪山花岗闪长岩体附近的逆断层富集成矿。     

Glacier meltwater runoff process analysis using δD and δ<Superscript>18</Superscript>O isotope and chemistry at the remote Laohugou glacier basin in western Qilian Mountains,China

Stable hydrogen and oxygen isotope has important implication on water and moisture transportation tracing research. Based on stable hydrogen (δD) and oxygen (δ¹⁸O) isotope using a Picarro L1102-i and water chemistry (e.g. major ions, pH, EC and TDS) measurement, this study discussed the temporal variation and characteristics of stable hydrogen and oxygen isotope, chemistry (e.g. TDS, pH, EC, Ca²⁺, Mg²⁺, Na⁺ and Cl^-) in various water bodies including glacier meltwater runoff, ice and snow, and precipitation at the Laohugou glacier basin during June 2012 to September 2013. Results showed that δD and δ¹⁸O in the meltwater runoff varied obviously with the temporal change from June to September, showing firstly increasing trend and then decreasing trend, with the highest values in July with high air temperature and strong glacier melting, which could indicate the temporal change of glacier melting process and extent. Variations of δD and δ¹⁸O in the runoff were similar with that of snow and ice on the glacier, and the values were also above the GMWL, which probably implied that the glacier runoff was mainly originated from glacier melting and precipitation supply. The glacier meltwater chemical type at the Laohugou glacier basin were mainly composed by Ca-Na-HCO₃-SO₄ and Ca-Mg-HCO₃-SO₄, which also varied evidently with the glacier melting process in summer. By analyzing the temporal change of stable hydrogen and oxygen isotope and chemistry in the melting period, we find it is easy to separate the components of the snow and ice, atmospheric precipitation and melt-runoff in the river, which could reflect the change process of glacier melting during the melting period, and thus this work can contribute to the glacier runoff change study of large-scale region by stable isotope and geochemical method in future.     

A modified method to estimate eddy diffusivity in the North Pacific using altimeter eddy statistics

The method proposed by Stammer (1998) is modified using eddy statistics from altimeter observation to obtain more realistic eddy diffusivity (K) for the North Pacific. Compared with original estimates, the modified K has remarkably reduced values in the Kuroshio Extension (KE) and North Equatorial Counter Current (NECC) regions, but slightly enhanced values in the Subtropical Counter Current (STCC) region. In strong eastward flow areas like the KE and NECC, owing to a large difference between mean flow velocity and propagation velocity of mesoscale eddies, tracers inside the mesoscale eddies are transported outside rapidly by advection, and mixing length L is hence strongly suppressed. The low eddy probability (P) is also responsible for the reduced K in the NECC area. In the STCC region, however, L is mildly suppressed and P is very high, so K there is enhanced. The zonally-averaged K has two peaks with comparable magnitudes, in the latitude bands of the STCC and KE. In the core of KE, because of the reduced values of P and L, the zonally-averaged K is a minimum. Zonally-integrated eddy heat transport in the KE band, calculated based on the modified K, is much closer to the results of previous independent research, indicating the robustness of our modified K. The map of modified K provides useful informationfor modeling studies in the North Pacific.     

土壤热扩散率及其温度、热通量计算方法的比较研究

本文利用绿洲系统能量与水分循环过程观测试验的2005年6月11日至15日在甘肃金塔绿洲中部观测的土壤温度、湿度和通量资料,在分析了观测期间土壤温度、湿度和通量特征的基础上,采用振幅法、相位法、谐波法和热传导对流法计算了5~20 cm土壤层的土壤热扩散率.在此基础上,以深度为5 cm的土壤层为上边界条件,计算了10 cm、20 cm深度的土壤温度和10 cm深度的热通量.结果表明:谐波法能很好地计算土壤温度,10 cm和20 cm深度的计算值相对观测值的标准差分别为:0.21 ℃和0.18 ℃;热传导对流法计算的土壤温度好于振幅法和相位法,但由于忽略了土壤水分通量密度的日变化,该方法用于土壤含水量有明显日变化的浅层土壤时,会出现计算误差.谐波法的计算土壤热通量与实测值最为接近,计算值与实测值的相关系数达到0.868.     

Two‐dimensional model of diffusion processes around a river mouth

The steady state diffusion equation is solved for two‐dimensional flow around a point source along an infinite straight boundary. Solutions obtained are related to the observed distribution of temperature and salinity around the mouth of the Buller River, South Island, New Zealand.     

陕西南沙河地区车渡金矿床成因

针对陕西南沙河地区车渡金矿床进行了研究,研究结果表明,中—新元古界碧口群二亚群(Pt2-3bk2)中玄武质火山凝灰岩具Sr、Ba、Rb、Ce、P、Sm相对富集,Ta、Nb、Zr、Hf、Ti相对亏损的特征,显示钙碱性火山弧玄武岩的特点;车渡金矿床具有2种成因类型,一是与中生代逆冲推覆构造形成的韧性剪切带有关的强硅化蚀变岩型金矿,二是与中—新元古界碧口岩群二亚群火山凝灰岩有关的BIF型金矿。单颗粒磁铁矿成分分析认为,车渡含金磁铁石英岩中磁铁矿具有高的TFeO(平均值99.59%)含量和极低的TiO_2、MgO、A_(12)O_3、MnO含量,指示车渡磁铁石英岩金矿石中条带状磁铁矿属于沉积变质型成因条带状含铁建造。含金磁铁石英岩型金矿石的氢氧同位素显示,δ~(18)O_水值为12.34‰～12.45‰(平均值12.40‰),δD值为-112.6‰～-103.5‰(平均值-108.05‰),与鞍山—本溪地区条带状含铁建造型铁矿δD变化范围(-129‰～-75‰)一致,暗示车渡含金磁铁石英岩中石英矿物具有条带状含铁建造特征。     

Experimental study on unsaturated soil water diffusivity in different soils in Hebei Piedmont Plain

Horizontal soil column method was used to determine the horizontal diffusion rate of sandy loam, loam and clay loam under the same bulk density. The results showed that the migration rates of different lithological wet fronts were different. The sandy loam had the fastest migration rate, the loam followed, and the clay loam was the slowest, but the law of change is the same among the three lithologies. The volumetric water content affects the change of Boltzmann parameter λ. When the volumetric water content is between 0.35-0.45 cm~3/cm~3, λ approaches stability. When the volumetric water content is less than 0.35 cm~3/cm~3, the λ value decreases rapidly with the decrease of water content. The water diffusion rate is related to the volumetric water content and particle size. The greater the moisture content is, the greater the diffusion rate will be. The larger the particle size, the larger the diffusion rate. The diffusivity of sandy loam is 10-30 times larger than that of loam and clay loam. The relationship between water content and diffusion rate is in accordance with the exponential function.     

Origins of High H_2S-bearing Natural Gas in China

Natural gas containing hydrogen sulphide （H2S） has been found in several petroliferous basins in China, such as the Sichuan Basin, Bohai Bay Basin, Ordos Basin, Tarim Basin, etc. Natural gas with higher HES contents （HES 〉5 % mol.） is mostly distributed in both the gas reservoirs of Dukouhe, Luojiazhai, Puguang and Tieshanpo, which belong to the Triassic Feixianguan Formation in the northeastern Sichuan Basin and those of the Kongdian-Shahejie formations in the northeastern Jinxian Sag of the Jizhong Depression, Bohai Bay Basin. In the Sichuan Basin, the HES contents of natural gas average over 9% and some can be 17 %, while those of the Bohai Bay Basin range from 40 % to 92 %, being then one of the gas reservoirs with the highest H2S contents in the world. Based on detailed observation and sample analysis results of a total 5000 m of core from over 70 wells in the above-mentioned two basins, especially sulfur isotopic analysis of gypsum, brimstone, pyrite and natural gas, also with integrated study of the geochemical characteristics of hydrocarbons, it is thought that the natural gas with high HES contents resulted from thermochemical sulfate reduction （TSR） reactions. Among them, the natural gas in the Feixianguan Formation resulted from TSR reactions participated by hydrocarbon gas, while that in the Zhaolanzhuang of the Jinxian Sag being the product of TSR participated by crude oil. During the consumption process of hydrocarbons due to TSR, the heavy hydrocarbons were apt to react with sulfate, which accordingly resulted in the dry coefficient of natural gas increasing and the carbon isotopes becoming heavier.