沙漠微生物矿化覆膜及其稳定性的现场试验研究

将微生物诱导矿化技术应用于原位沙漠覆膜的形成,使得流动沙丘经结皮固定而成为半固定、固定沙丘,从根本上阻断沙尘暴的源头。在内蒙古乌兰布和沙漠腹地选择两个微生物矿化试验区域（TP1和TP3）,分别用于两种不同矿化菌种诱导生成碳酸钙覆膜。研究沙漠微生物矿化覆膜的现场试验方法及工艺,对原位矿化覆膜的强度及其在沙漠环境中的长期稳定性进行跟踪检测。采用沙漠土中自行提取的葡萄球菌和传统的巴氏芽孢杆菌两种不同的微生物矿化菌种,通过现场贯入试验检测7、14、28、60、210 d后矿化覆膜沿深度发展的贯入阻力,并将覆膜厚度为2 cm处的平均贯入阻力换算成覆膜层强度,总结覆膜强度随时间的发展变化规律。现场观测结果显示,不同微生物菌种诱导生成的矿化覆膜均在试验的第4天开始形成,到第7天覆膜层具有稳定的强度和厚度,现场检测覆膜的平均厚度为2.0～2.5 cm,经自源葡萄球菌诱导生成的矿化覆膜（TP1）的强度是巴氏芽孢杆菌诱导生成的矿化覆膜（TP3）强度的1.05倍。当经历冬春交替后覆膜层强度都有不同程度的降低,明显地TP3较TP1区域表面剥落更为严重,第210天检测TP3的平均厚度为0.7～1.0 cm,覆膜强度较第7天时降低19%,覆膜内碳酸钙含量较第7天检测时降低15%～30%。而TP1在第210天时的强度较第7天时强度降低仅2%。因此,微生物诱导矿化技术可以应用于沙漠原位覆膜的形成,且沙漠自源葡萄球菌经诱导生成的矿化覆膜层具有更好的强度表现和稳定性。     

鄂尔多斯盆地渭北地区上三叠统延长组长7油层组碳酸盐结核中自生碳酸盐矿物的特征

早期形成的碳酸盐结核在埋藏期间会经历多种碳酸盐矿物相沉淀的复杂胶结作用,岩石学研究是探究结核成因的关键。通过野外剖面观察、岩石学观察和阴极发光技术,分析了鄂尔多斯盆地渭北地区上三叠统延长组长7油层组泥页岩中各种形状的方解石和白云石结核中自生碳酸盐矿物的特征。这些结核为成岩早期的产物,构成结核的自生碳酸盐矿物特征显著:(1)球粒方解石结核中,方解石呈纤维状或刃片状,球粒间充填晶粒方解石或因压实呈贴面结合,纤维状方解石发桔红色和暗红色2种光,刃片状方解石发暗红色光;(2)粉晶方解石结核中,方解石呈他形粒状,含有机质包裹体或纤维状晶形残余,晶间含沥青和纤维状方解石残余,主要发暗红色光;(3)白云石结核有泥晶和粉晶2种晶体类型,粉晶白云石结核含较多泥质,泥质条带或有机质条带处常见纤柱状白云石;(4)沿裂缝充填的方解石和白云石常呈纤维状或纤柱状结构,发暗红色光或不发光。研究区长7油层组碳酸盐结核中的方解石和白云石具有不同的成因类型和复杂的胶结作用:球粒方解石和泥晶白云石代表了结核开始形成时的胶结作用,可以准确地反映结核的成因;粉晶方解石、粉晶白云石反映了交代成因;裂缝中纤维状、纤柱状方解石和白云石集合体则为结核经历了较强压实作用之后充填裂缝而成。     

Calibration of oxygen isotope fractionation and calcite-corundum thermometry in emery at Naxos,Greece

Corundum (Crn), including sapphire, occurs in emery pods surrounded by marble on the island of Naxos, Greece. The emery formed from bauxite deposited in karst that was metamorphosed to 400–700°C at 20–15 Ma. Many of these rocks initially appeared well suited for refractory accessory mineral (RAM) thermometry, which uses oxygen isotope fractionation between a RAM – corundum – and a modally dominant phase with faster diffusion of oxygen – calcite (Cc) – to determine peak metamorphic temperatures. However, previous attempts at oxygen isotope thermometry were confounded by highly variable fractionations (Δ¹⁸O) measured at mm-scale and the uncertain calibration of Δ¹⁸O(Cc-Crn) versus temperature. Secondary ion mass spectrometry (SIMS) permits in situ analysis of δ¹⁸O in corundum and calcite at the 10-μm scale in adjacent grains where textures suggest peak metamorphic equilibrium was attained. SIMS analyses of adjacent mineral pairs in eight rocks yield values of Δ(Cc-Crn) that systematically decrease from 7.2 to 2.9‰ at higher metamorphic grade. Pairing these data with independent temperature estimates from mineral isograds yields an empirical calibration of 1,000 lnα(Cc-Crn) = 2.72 ± 0.3 × 10⁶/T² (T in K). The new fractionations (2.7‰ at 1,000 K) are significantly smaller than those calculated from the modified increment method (6.5‰ at 1,000 K; Zheng, Geochimica et Cosmochimica Acta, 1991, 55:2299–2307; Zheng, Mineral Mag, 1994, 58A:1000–1001), which yield unreasonably high temperatures of 630 to 1,140°C when applied to the new Naxos data. The new calibration of Δ(Cc-Crn) can be combined with published fractionations to calculate A-factors for corundum versus a range of 14 other minerals. These new fractionation factors can be used for thermometry or to constrain the genesis of corundum. A compilation of gem corundum δ¹⁸O values shows that many igneous sapphires, including important deposits of basalt-associated sapphire, are mildly elevated in δ¹⁸O relative to the calculated range in equilibrium with mantle values (4.4–5.7‰) and formed from evolved magmas.     

Climatic signals in lacustrine deposits of the Upper Yacoraite Formation,Western Argentina: Evidence from clay minerals,analcime, dolomite and fibrous calcite

Authigenic clays are an important control on reservoir quality in lacustrine carbonates but remain challenging to predict. Lacustrine depositional systems respond to climatic variations in rainfall, surface runoff and groundwater input, and evaporation, and result in rapid and frequent changes in lake volume; this is expressed through changing water depth and shoreline position. In the upper portion of the Early Palaeocene Yacoraite Formation of the Salta Basin in Argentina, extensive lacustrine deposits were deposited during the sag phase of rifting. Prior high-resolution stratigraphic studies have suggested that climatic factors control microbial carbonate sequences within a ‘balanced fill’ lake, with variation in the lake level having a major influence on facies association changes. This study characterizes the evolution of facies and mineralogy within the Yacoraite Formation, focusing on the distribution of clay minerals, making a link between the high, medium and low-frequency sequence stratigraphic cycles. The low-frequency transgressive hemicycle of the upper portion of the Yacoraite Formation is comprised of abundant siliciclastic facies, suggesting a wetter period. Microbialites occurring in this interval are coarse-grained and agglutinated. Detrital clay minerals such as illite and chlorite and associated siliciclastic sediments were input to the lake during high-frequency transgressive periods. During high-frequency regressive hemicycles, sedimentation was dominated by carbonate facies with Ca-rich dolomite and the authigenic clays are comprised of chlorite/smectite mixed-layers. By contrast, the low frequency regressive hemicycle records fine-grained agglutinated microbialite with horizons of fibrous calcite, more stoichiometric dolomite, barite and authigenic magnesian smectite. This indicates elevated ion concentrations in the lake under intense evaporation during an arid period. Understanding the conditions that are favourable for formation and preservation of authigenic clays within the lacustrine environment can improve understanding of reservoir quality in comparable economically important deposits.     

The origin of magnetization and geochemical alteration in a fault zone,Kilve, England

The origin of an apparently syndeformational chemical remanent magnetization (CRM) and geochemical alteration in a fault zone in the Bristol Channel Basin, southwest England, was investigated. Deformation in the fault zone occurs in Jurassic aged, organic-rich limestones and consists of numerous normal and oblique-slip faults and associated folds. Migration of basinal, radiogenic fluids is indicated by elevated ⁸⁷Sr/⁸⁶Sr values for calcite veins that occur throughout the fault zone. Some of the calcite veins contain hydrocarbons sourced from deeper strata. Elevated ⁸⁷Sr/⁸⁶Sr values in the host Jurassic limestones indicate that they were also extensively altered by radiogenic fluids that migrated through microfractures in addition to major fault and fracture planes. Folded and tilted host limestones contain a pervasive secondary CRM residing in magnetite that was acquired during deformation in the Tertiary. The association between this pervasive CRM and the pervasive geochemical alteration is consistent with a genetic connection between the orogenic fluids and the CRM although the timing of CRM acquisition (Tertiary) is not consistent with structural interpretations for the timing of most veining. An alternative remagnetization mechanism which is not triggered by externally derived fluids, such as diagenesis of hydrocarbons, might account for the CRM. Hydrocarbon-bearing veins also contain a CRM that resides in magnetite, although the time for remanence acquisition is not well constrained by field tests. © 1998 John Wiley & Sons, Ltd.     

地层水条件下碳酸盐矿物热力学平衡条件及其在克拉2气田的应用

基于热力学平衡理论及库车盆地的实际,建立了该区地层水温度、压力条件下方解石溶解、白云石对方解石交代作用的热力学平衡条件,并根据地层水介质特征探讨了该区方解石溶解、白云石交代方解石的具体成岩反应状况,认为该区地层水条件下正进行着方解石溶蚀及白云石对方解石的交代作用,方解石的溶蚀是形成该区深层次生孔隙的根本因素。      

Geochemistry and genesis of authigenic pyrite from gas hydrate accumulation system in the Qilian Mountain permafrost,Qinghai, northwest China

A type of authigenic pyrites that fully fill or semi-fill the rock fractures of drillholes with gas hydrate anomalies are found in the Qilian Mountain permafrost; this type of pyrite is known as “fracture-filling” pyrite. The occurrence of “fracture-filling” pyrite has a certain similarity with that of the hydrate found in this region, and the pyrite is generally concentrated in the lower part of the hydrate layer or the hydrate anomaly layer. The morphology, trace elements, rare earth elements, and sulfur isotope analyses of samples from drillhole DK-6 indicate that the “fracture-filling” pyrites are dominated by cubic ones mainly aligned in a step-like fashion along the surfaces of rock fractures and are associated with a circular structure, lower Co/Ni and Sr/Ba, lower ΣREE, higher LREE, significant Eu negative anomalies, and Δ³⁴S_CDT positive bias. In terms of the pyrites’ unique crystal morphology and geochemical characteristics and their relationship with the hydrate layers or abnormal layers, they are closely related with the accumulation system of the gas hydrate in the Qilian Mountain permafrost. As climate change is an important factor in affecting the stability of the gas hydrate, formation of fracture-filling pyrites is most likely closely related to the secondary change of the metastable gas hydrate under the regional climate warming. The distribution intensity of these pyrites indicates that when the gas hydrate stability zone (GHSZ) is narrowing, the hydrate decomposition at the bottom of the GHSZ is stronger than that at the top of the GHSZ, whereas the hydrate decomposition within the GHSZ is relatively weak. Thus, the zone between the shallowest and the deepest distribution of the fracture-filling pyrite recorded the largest possible original GHSZ.     

Within‐colony variation in skeletal mineralogy of Adeonellopsis sp. (Cheilostomata: Bryozoa) from New Zealand

Three colonies of the erect, robust branching, cheilostome bryozoan Adeonellopsis sp. were collected from Doubtful Sound, New Zealand, to investigate within‐colony variation in carbonate mineralogy. One‐hundred‐and‐twenty‐one sections from 9 branches were found to contain mostly aragonite, with calcite ranging from 1.1 to 7.3 wt% (mean ± SD = 2.4 ± 1.2 wt%, n = 120). The magnesium (Mg) content in calcite ranged from 5.3 to 13.1 wt% magnesium carbonate (8.8 ± 1.0 wt% MgCO₃; n = 120). Calcite content decreased with increasing age proximally along the branch, indicating that secondary thickening is achieved with aragonite. In contrast, an oscillating trend in Mg content along branches suggests that seasonal or interannual environmental parameters may influence this geochemical parameter. Mineralogical variability highlights the need for multiple samples from the same colony to be measured when determining quantitative carbonate mineralogy in bryozoans. Bimineralic bryozoans such as Adeonellopsis sp. may have lower preservation potential than monomineralic bryozoans, and consequently may not survive diagenesis to become fossils. Bimineralic species may also be more vulnerable to dissolution pressure and possible ocean acidification than monomineralic calcitic taxa.     

湖泊自生碳酸盐碳同位素在环境变化中的应用

湖泊自生碳酸盐碳同位素组成(δ13Cc)在区域气候与环境变化方面的应用研究近年来进展迅速,成果显著,保存在各类湖泊沉积物柱芯中的δ13Cc记录揭示了湖表水体与大气CO2的交换程度、暖季降水量的多少、流域C3和C4植被变化情况、水生生物光合作用或呼吸作用强弱、湖泊生产力大小、湖泊水体化学特征、湖水不同深度层的有机质变化过程等重要的气候和环境信息;对此进行归纳和述评。     

赣南6722铀矿床方解石Sm-Nd等时线年龄及其地质意义

6722热液型铀矿床位于东西向南岭构造和北东向武夷隆起交汇部位的禾草坑铀矿田内。本文利用采集于该矿床花岗岩型矿石中的8件方解石进行Sm-Nd年龄测定,确定了成矿年龄为113.4±6.9 Ma。这期发生在花岗岩中的铀矿化早于隐爆角砾岩中的矿化。我们推测前期花岗岩中的矿化为后期隐爆角砾岩中富矿体的形成提供了预富集。白垩纪时6722矿床所在会昌地区处于岩石圈伸展的地段,伸展作用为铀成矿创造有力条件,岩石圈伸展与铀成矿之间具有良好的对应关系。