Thermodynamic conditions of framework grain dissolution of clastic rocks and its application in Kela 2 gas field

Feldspar and clastic debris are the most important constituent framework grains of sedimentary clastic rocks and their chemical dissolution plays an essential role in the formation and evolution of the secondary pore in the reservoir rocks. On the basis of thermodynamic phase equilibrium, this study investigates the chemical equilibrium relationships between fluid and various plagioclase and K-feldspar in diagenesis of the sediments, particularly, the impact of temperature and fluid compositions (pH, activity of K+, Na+, Ca2+ and so on) on precipitation and dissolution equilibria of feldspars. Feldspar is extremely easily dissolved in the acid pore water with a low salinity when temperature decreases. The dissolution of anorthite end-member of plagioclase is related to the Ca content of the mineral and the fluid, higher Ca either in the mineral or in the fluid, easier dissolution of the feldspar. Moreover, the dissolution of albite end-member of plagioclase is related to Na of both the mineral and fluid,     

区域生态地球化学评价核心与对策

生态地球化学是地学与土壤学、农业、环境学和生态学等多学科交叉融合产生的新学科,是地球化学领域新的发展方向。区域生态地球化学评价是在区域地球化学调查基础上,针对影响流域/区带生态系统安全性的元素异常而开展的一项评价和研究工作。多目标区域地球化学调查获得的海量高精度地球化学数据,可为环境质量评价提供背景值、为土地的质量和生态管护提供地球化学依据;调查还发现了一系列影响流域生态安全性的元素异常,针对异常元素分布特征,区域生态地球化学评价将开展异常元素追踪和成因甄别、生态效应评价和生态系统安全性的预警预测等项评价和研究工作。文章论述了区域地球化学调查成果,介绍了区域地球化学评价的思路,阐述了区域生态地球化学评价的主要问题与对策。     

Modeling the influence of settling velocity on cohesive sediment transport in Tanshui River estuary

Settling velocities of suspended cohesive sediment in estuaries vary over a range of several orders in magnitude. Variations in the suspended sediment concentration are often considered as the principal cause. Turbulence and the suspended sediment concentration, as well as other factors such as salinity, dissolved organic substances, flocculation ability, and the rate of floc growth affect setting velocities. A laterally–averaged finite difference model for hydrodynamics and cohesive sediment transport is developed and applied in the Tanshui River estuary, Taiwan. The model has been calibrated and verified with water surface elevation, longitudinal velocity, salinity, and cohesive sediment measured. The overall performance of the model is in qualitative agreement with the available data. The model is used to investigate the influence of settling velocity on cohesive sediment transport dynamics. The simulation indicates that the turbidity maximum zone is near Kuan–Du. When settling velocities increase the surface cohesive sediment concentration at Kuan–Du station trends to decrease and bottom cohesive sediment concentration increases. Both surface and bottom cohesive sediment concentrations decrease at Taipei Bridge and Pa–Ling Bridge. This implies that suspended sediment advected seaward and deposited. There is consequently a net seaward flux of suspended sediment near surface, and a net landward flux near the bed.     

三峡库区巴东县城附近主要滑坡边界轨迹分形分维特征与滑坡稳定性关系

为了探索复杂滑坡轨迹结构演化及其稳定性定量分析计算的新途径，本文利用分形分维理论，分析三峡库区巴东县城附近滑坡边界轨迹的几何分形结构，并采用盒维数法分别求得巴东县城附近11个滑坡边界轨迹的分维值，计算结果表明：每个滑坡的轨迹结构具有其特征性的分维值，轨迹结构越复杂，结构层次越清楚，分维值越高；其中，榨房坪滑坡和黄腊石滑坡的分维值最高，分别为1.50和1.483，西壤口和谭家湾滑坡的分维值最低，分别为0.925和0.732；而黄土坡和赵树岭滑坡的分维值介于二者之间，分别为1.111和1.091。结合典型滑坡边界轨迹结构演化与滑坡稳定性关系的定性分析及前期滑坡稳定性定量计算和模拟分析，初步揭示：滑坡边界轨迹结构与稳定性是密切相关的，滑坡边界轨迹宏观扩展增值越明显，轨迹结构越复杂，分维值越高，其稳定性条件也越差，因此，分数维可作为衡量滑坡轨迹结构复杂性和稳定性的重要标志；滑坡边界轨迹宏观扩展变形存在一个极限，超过这个极限滑坡的局部失稳就转化为整体滑动；而滑坡边界轨迹则记录了滑坡变形扩展现象和信息，因此，相对应地滑坡轨迹分形结构的分维值也应存在一个极值，在极值点滑坡体处于临滑状态；滑坡边界轨迹结构的极限分维值大致为1.4～1.5，此时滑坡接近于整体极限失稳状态，而分维值在1.1～1.3之间则表示滑坡处于整体稳定，局部存在潜在失稳状态，分维值小于1则表示滑坡处于相对稳定状态。     

高喷灌浆技术在金哨电站厂房临时围堰防渗工程中的应用

通过金哨电站临时围堰高喷灌浆的防渗处理实例，介绍了高喷灌浆围堰防渗板墙的设计方法、施工工艺和防渗处理效果。     

Analysis of the environmental sensitivities of a typical dynamic epikarst system at the Nongla monitoring site, Guangxi, China

Nongla, a typical karst dynamic system (KDS) monitoring site, is located at Nongla Village, Mashan County, Guangxi, China. The data from a Greenspan CTDP300 multichannel data logger indicates that the KDS is highly sensitive to environmental changes. Multi-day and diurnal physico-chemical composition of epikarst spring water is quite different under different climatic conditions. During a day with no rainfall, water temperature and air temperature have similar variations. Electrical conductivity (EC) has good positive correlation with pH value and water temperature. During rainstorms, the physico-chemical composition of the spring water is initially strongly effected by dilution, pH and EC drop rapidly. However, half to one hour later, EC returns to normal and the CO₂ effects will be the dominant physical effect. This is due to the high fissure rates and high permeability in the epikarst zone. Dilution effects were observed during the entire rainstorm event,whereas, it only acts during the earliest period of light rain. Therefore, it is necessary to examine the water–rock–CO₂ combination as a whole system to explain the hydrochemical behavior of epikarst processes.     

Sr/Sr and Sr/Ca in speleothems for paleoclimate reconstruction in Central China between 70 and 280 kyr ago

Limestone cave deposits (speleothems) provide archives for past changes in regional climates over a range of timescales. While δ¹⁸O and δ¹³C in speleothem calcite have been commonly used for reconstruction of paleoclimates, we report here further efforts in the use of ⁸⁷Sr/⁸⁶Sr and Sr/Ca signals in speleothem calcite to deduce paleomonsoon variability near the Loess Plateau of central China. A two end-member mass-balance model of concentration and isotopic composition of strontium in a cave system is used to estimate variation of the ⁸⁷Sr/⁸⁶Sr ratio in sediments overlying a limestone cave. We show that this ratio reflects climate-driven variations in the provenance and the extent of chemical weathering of the epikarstic sediments. The measurements of ⁸⁷Sr/⁸⁶Sr made on a well-dated stalagmite, SFL, from Buddha Cave (33^o40N′ 109^o05′E) show ratios of 0.71092 to 0.71133 (±0.00001 as 2σ) during relatively cold periods (e.g., Marine Isotope Stage (MIS) 5b, 5d, and 8), lower than ratios of 0.71133 to 0.71194 during relatively warm periods (e.g., MIS 5a, 5c, 5e, and 7). As changes in the Sr/Ca ratio may affect speleothem ⁸⁷Sr/⁸⁶Sr, we show that the direct use of speleothem ⁸⁷Sr/⁸⁶Sr is less ideal than our modeled ⁸⁷Sr/⁸⁶Sr for the exogenic Sr source above the cave as a paleomonsoon proxy. Using the δ¹⁸O, δ¹³C, Sr/Ca, and ⁸⁷Sr/⁸⁶Sr records of the stalagmite, we reconstruct the variability of the East Asian monsoon for the time period between 70 and 280 kyr ago. The results show that summer monsoons were more intense during interglacial periods than during glacial periods.     

Effects of temporal scales and space mismatches on the TRMM 3B42 v7 precipitation product in a remote mountainous area

The accurate measurement of precipitation is essential to understanding regional hydrological processes and hydrological cycling. Quantification of precipitation over remote regions such as the Tibetan Plateau is highly unreliable because of the scarcity of rain gauges. The objective of this study is to evaluate the performance of the satellite precipitation product of tropical rainfall measuring mission (TRMM) 3B42 v7 at daily, weekly, monthly, and seasonal scales. Comparison between TRMM grid precipitation and point‐based rain gauge precipitation was conducted using nearest neighbour and bilinear weighted interpolation methods. The results showed that the TRMM product could not capture daily precipitation well due to some rainfall events being missed at short time scales but provided reasonably good precipitation data at weekly, monthly, and seasonal scales. TRMM tended to underestimate the precipitation of small rainfall events (less than 1 mm/day), while it overestimated the precipitation of large rainfall events (greater than 20 mm/day). Consequently, TRMM showed better performance in the summer monsoon season than in the winter season. Through comparison, it was also found that the bilinear weighted interpolation method performs better than the nearest neighbour method in TRMM precipitation extraction.