Geochemistry of carbonate precipitation from the groundwater in a coastal region

Groundwater samples were collected from a coastal region of Andhra Pradesh to assess the possible conditions of the formation of carbonates. The area experiences a semi-arid climate and is underlain by khondalites, over which the Quaternary sediments occur. The study of the geochemistry of groundwater indicates that groundwater is mostly of fresh, with alkaline nature. The study further suggest that the breakdown of feldspars as kaolinite during rock-water interaction, releases Ca²⁺. Soils/weathered products contribute high CO₂ under the open system. The Ca²⁺ and CO₂ are added to the groundwater through the infiltrating recharge water. They subsequently precipitate as fine-grained carbonates in the weathering profile due to evapotranspiration under a freshwater environment.     

Evaluation of distributed recharge in an upland semi-arid karst system: the West Bank Mountain Aquifer,Middle East

Assessment of recharge in a structurally complex upland karst limestone aquifer situated in a semi-arid environment is difficult. Resort to surrogate indicators such as measurement of spring outflow and borehole discharge, is a common alternative, and attempts to apply conventional soil moisture deficit analysis may not adequately account for the intermittent spate conditions that arise in such environments. A modelling approach has been made using the West Bank Mountain Aquifer system in the Middle East as a trial. The model uses object oriented software which allows various objects to be switched on and off. Each of the main recharge processes identified in the West Bank is incorporated. The model allows either conventional soil moisture deficit analysis calculations or wetting threshold calculations to be made as appropriate, and accommodates both direct recharge and secondary recharge. Daily time steps enable recharge and runoff routing to be calculated for each node. Model runs have enabled a series of simulations for each of the three aquifer basins in the West Bank and for the whole of the West Bank. These provide recharge estimates comparable to those prepared by earlier workers by conventional means. The model is adaptable and has been successfully used in other environments.     

海洋沉积物中的钒、钼、铊、镓及其环境指示意义

研究探讨沉积物中钒、钼、铊和镓的生物地球化学行为对揭示海洋环境演变机制有重要的科学意义,基于此考虑,本文系统分析总结了近年来海洋沉积物中V、Mo、Tl和Ga的地球化学特征以及与环境关系的研究进展,以期对深入开展环境敏感微量元素的海洋生物地球化学有所裨益。结果表明,由于受人为输入的影响,近海沉积物中V、Mo、Tl和Ga含量高于远海,河口高于近海;在表层沉积物中,细颗粒沉积物中V、Mo、Tl和Ga含量高于粗颗粒中的,且其含量与物源、有机质含量等沉积环境因素密切相关;在垂直分布上,随沉积物深度的增加,V、Mo、Tl和Ga含量趋于降低,表明近几十年来,随人为影响的加剧,海洋作为地球上物质的汇获得了比以前更多的V、Mo、Tl和Ga。由此可见,在水平方向上,海洋沉积物中V、Mo、Tl和Ga的丰度可表明输入物源的特性,而在柱状样中的垂直分布,则能够表征历史年代上V、Mo、Tl和Ga沉积量的差异。由于沉积物中V、Mo、Tl和Ga的性质比较稳定,它们在一定程度上可以揭示和表征海洋环境演变的讯息,追溯海洋环境演变的历史以及预测将来的发展趋向。     

大同盆地砷中毒病区沉积物中砷的吸附行为和影响因素分析

沉积物对砷的吸附-解吸作用是控制砷在地下水中的迁移和转化的决定性因素。对砷中毒重病区大同盆地山胡县沉积物中砷的吸附行为和影响因素研究结果表明,沉积物对砷的吸附符合Freundlich吸附等温模式,吸附量主要与沉积物颗粒大小、黏土矿物质量分数和类型、铁铝氧化物质量分数以及沉积物中As的质量分数有关,有机质质量分数对砷的吸附量影响需进一步深入研究。铝硅酸盐、铁铝氧化物质量分数较高且颗粒较细的黏土和亚黏土类沉积物对砷的吸附性较强;而铝硅酸盐、铁铝氧化物质量分数较低且颗粒较粗的细砂和粉砂类沉积物对砷的吸附性较差,其所处的含水层也是形成高砷地下水的主要含水层。pH值为5．5～8．0时,砷的吸附量最大。大同盆地高砷地下水pH条件非常不利于沉积物中砷的吸附,易形成高砷地下水。该区地下水10℃左右的温度条件非常有利于沉积物对砷的吸附,但由于影响因素较多,且地下水的温度在不同季节会发生一定的变化,其产生的影响还有待进一步研究。     

某盆地油气勘查成本预算和风险分析

某高原盆地的油气资源量较为丰富，可找到大型油气田。根据含油气盆地地质构造特征、生油岩的厚度与热演化程度、储集层和区域性盖层的发育情况等因素，确定了两个含油气远景区，拟作为重点找油气靶区。提出了两个可供选择的油气勘探布署方案。在此基础上，选用适当的成本预算基本参数，进行油气勘查成本估算，并对两个方案进行了优选对比与具体的风险分析，提出方案决策意见。     

八面河地区原油、烃源岩中甾类化合物的分布特征及其应用

对渤海湾盆地八面河地区31个分别形成于还原性咸化水体和淡水环境的页岩和泥岩样、20个油样中甾类化合物进行了剖析。结果表明该区烃源岩、原油中的甾类化合物异常丰富，主要包括C27－29规则甾烷、C28－304－甲基甾烷、甲藻甾烷以及芳香甾类；不同层段烃源岩中甾类化合物的分布各具特色，发育于牛庄洼陷南斜坡咸化水体的富藻类沙四段页岩富含4－甲基甾烷及甲藻甾烷，形成于淡水环境的沙三段泥岩中甲藻甾烷不太发育。烃源岩、原油中规则甾烷的分布型式明显有别于甲基甾烷，指示两类化合物可能来源于不同的藻类属种。甾类化合物的分布特征受控于古环境、生物先质种类及热成熟度等多种因素。不同层段甾类化合物的特征性分布使其成为该区油源岩确认的关键指标。结果还表明，甲基甾烷在油源岩识别中比规则甾烷具有更好的应用效果。依据甾类化合物，可判断埋深超过2700m的Es4烃源岩与原油具有较好的相关性，发育于牛洼洼陷南斜坡的未熟－低熟特殊烃源岩－富藻类页岩与原油没有可比性，该结论是对近期油源调查结果的进一步确认。     

Late Pleistocene sea-level oscillations (MIS 10–2) recorded in shallow marine and coastal plain sediments of the southern Wanganui Basin, New Zealand

The northern Wanganui Basin, New Zealand, is one of the key global sites for understanding marine cyclic sedimentation during the Quaternary. This paper presents the first evidence of marine cyclic sedimentation from its central-southern parts. Sedimentological, micropalaeontological and palynological analyses on a 280-m-deep borehole encountered units dating back to MIS 10. The sequence includes four marine cycles spanning MIS 9–5, which are overlain by terrestrial fluvial aggradation surfaces dating from MIS 4–2. Each marine unit represents a progressively shallowing depositional environment from the mid-shelf to coastal plain. This is overlain by a terrestrial sequence of lowstand fluvial terraces. Localized fault movements appear to have influenced the sedimentary character of the sequence during MIS 7a and 5e producing basement highs which provided protection to the shoreline. The cyclothems described in this paper now extend the already extensive, previously described record from MIS 17–10 to produce a combined eustatic record of Quaternary sea level change within the basin to MIS 5. They also provide an excellent example of the sedimentary response of a coastal basin to a progressive loss of sedimentation accommodation space.     

多金属结核的沉积物地球化学场

远洋沉积物是多金属结核赖以生长的场所，本文系统地研究了沉积物中主要成矿元素水成组分在不同地球化学场和不同沉积阶段的地球化学特征，以及水成组分的含量比与成矿作用的相互关系。研究表明，Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ都是一些比较活泼的元素，它们共处于多金属结核、沉积物和大洋水的统一体系中，当结核形成时，Ｍｎ、Ｆｅ、Ｎｉ、Ｃｕ在结核与沉积物中的含量呈负相关，而Ｃｏ含量呈正相关。研究区东部结核以富含Ｍｎ、Ｎｉ、Ｃｕ贫Ｆｅ、Ｃｏ为特征，其伴生沉积物相对贫Ｍｎ、Ｎｉ、Ｃｕ、Ｃｏ，而富Ｆｅ，可称之为贫化的地球化学场。研究区西部结核富含Ｆｅ、Ｃｏ而贫Ｍｎ、Ｎｉ、Ｃｕ，其伴生沉积物则相应贫Ｆｅ，而富Ｍｎ、Ｎｉ、Ｃｕ、和Ｃｏ，可称之为富化的地球化学场。可以看出，贫化的沉积物地球化学场，恰恰是寻找富矿结核的最佳场所。早中新世以来的沉积物，根据水成组分的含量或含量比，也可相应于结核的形成分为三大沉积阶段，其中的第Ⅱ阶段具有贫化的地球化学特征，是多金属结核形成的最有利时期     

Subbottom acoustic and sedimentary records of past surface water–groundwater exchange through sinkhole lakes in south Georgia,U.S.A

Lake Balboa is a deep sinkhole lake in south Georgia. Subbottom acoustic profiling and long sediment cores reveal four stratigraphic units within >20 m of lacustrine fill above acoustically stratified and faulted Miocene/Pliocene overburden and basement Eocene limestone which hosts the Floridan Aquifer system (FAS). Fill consists of thin, rhythmically bedded, peaty sediments (Unit I), indicative of slow sedimentation in a shallow swamp until 13,110–12,680 cal BP, a mix of desiccated and over-consolidated clay and silty sand (Unit II) implying periodic subaerial exposure of the lake bed until 9470–9025 cal BP, and gyttja associated with a rapid 8 m rise in water level by 9120–9020 cal BP (Unit III), as well as an additional rise of 10 m to modern lake levels (Unit IV). Accumulation of nearly 4.5 m of low permeability gyttja, and higher lake levels have fundamentally changed exchange between surface water and groundwater, reducing by 40% or more the rate of vertical leakage to the FAS and increasing shallow aquifer discharge to the lake.     

沉积物物源定量识别的非线性规划模型——以东海陆架北部表层沉积物物源识别为例

依据“质量守衡”原理和沉积物物源难以穷尽的认识 ,提出了沉积物物源定量识别的非线性规划数学模型。利用该模型实现了东海陆架北部表层沉积物物源的定量计算 ,阐明了长江、黄河入海物质的大致分布特征。长江沉积物主要分布于 32°N以南、台湾暖流以西的海域 ,黄河沉积物主要分布于 32°N以北、台湾暖流以东的海域。长江、黄河两类沉积物的这种分布格局与本海域的流系分布相吻合。