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《Applied Geochemistry》2004,19(5):645-664
Sediment and water samples from 12 saline pans on the semi-arid west coast of South Africa were analysed to determine the origin of salts and geochemical evolution of water in the pans. Pans in the area can be subdivided into large, gypsiferous coastal pans with 79–150 g/kg total dissolved salt (TDS), small inland brackish to saline (2–64 g/kg TDS) pans and small inland brine (168-531 g/kg TDS) pans that have a layer of black sulphidic mud below a halite crust. The salinity of coastal pan waters varies with the seasonal influx of dilute runoff and dissolution of relict Pleistocene marine evaporite deposits. In contrast, inland pans are local topographic depressions, bordered on the north by downslope lunette dunes, where solutes are concentrated by evaporation of runoff, throughflow and groundwater seepage. The composition of runoff and seepage inflow waters is determined by modification of coastal rainfall by weathering, calcite precipitation and ion exchange reactions in the predominantly granitic catchment soils. Evaporation of pan waters leads to precipitation of calcite, Mg–calcite, dolomite, gypsum and halite in a distinct stratigraphic succession in pan sediments. Bicarbonate limits carbonate precipitation, Ca limits gypsum precipitation and Na limits halite precipitation. Dolomitisation of calcite is enhanced by the high Mg/Ca ratio of brine pan waters. Brine pan waters evolve seasonally from Na–Cl dominated brines in the wet winter months to Mg–Cl dominated brines in the dry summer months, when 5–20 cm thick halite crusts cover pan surfaces. Pan formation was probably initiated during a drier climate period in the early Holocene. More recent replacement of natural vegetation by cultivated land may have accelerated salt accumulation in the pans. 相似文献
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电感耦合等离子体发射光谱法同时测定卤水中锂钠钾钙镁硼硫氯 总被引：5，自引：2，他引：3
建立了电感耦合等离子体发射光谱法(ICP-AES)同时测定碳酸盐型、硫酸盐型、氯化物型三种类型卤水中Li、Na、K、Ca、Mg、B、S、Cl等高低含量元素的分析方法。选择仪器最佳的工作条件为射频功率1400W,炬管位置位于-3,载气流量0.60 L/min。确定了各元素测定谱线,使用ICP-AES的双向观测模式、轴向观测模式测定Li、Ca、B、S、Cl以及低含量的K、Mg,径向观测模式测定高含量的Na、K、Mg,可确保卤水中不同含量的元素同时检出。Li、Na、K、Ca、Mg、B、S的检测下限为0.07～3.00 mg/L,Cl的测定下限为165mg/L。方法精密度(RSD,n=10)均小于5%,回收率为92.4%～109.7%。其中Na、K、Mg、S、Cl测定结果与传统方法测定结果基本吻合。 相似文献
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Lake Qarun is an inland saline lake of the type Na---(Mg)---Cl---(SO4). The SO4/Cl weight ratio exceeds 0.6. The sequence of salt deposition, upon mechanical evaporation at 70°C, starts with basanite and halite, passes with magnesium sulphate minerals and ends with sylvite and carnallite. High concentrations of Sr in the gypsiferous fraction and B in the end-residue are recorded. 相似文献
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M. Schmidt R. Botz E. Faber M. Schmitt J. Poggenburg D. Garbe-Sch nberg P. Stoffers 《Chemical Geology》2003,200(3-4):359-375
A decrease in temperature (ΔT up to 45.5 °C) and chloride concentration (ΔCl up to 4.65 mol/l) characterises the brine–seawater boundary in the Atlantis-II, Discovery, and Kebrit Deeps of the Red Sea, where redox conditions change from anoxic to oxic over a boundary layer several meters thick. High-resolution (100 cm) profiles of the methane concentration, stable carbon isotope ratio of methane, and redox-sensitive tracers (O2, Mn4+/Mn2+, Fe3+/Fe2+, and SO42−) were measured across the brine–seawater boundary layer to investigate methane fluxes and secondary methane oxidation processes.
Substantial amounts of thermogenic hydrocarbons are found in the deep brines (mostly methane, with a maximum concentration up to 4.8×105 nmol/l), and steep methane concentration gradients mainly controlled by diffusive flow characterize the brine–seawater boundary (maximum of 2×105 nmol/l/m in Kebrit Deep). However, locally the actual methane concentration profiles deviate from theoretical diffusion-controlled concentration profiles and extremely positive δ13C–CH4 values can be found (up to +49‰ PDB in the Discovery Deep). Both, the actual CH4 concentration profiles and the carbon-13 enrichment in the residual CH4 of the Atlantis-II and Discovery Deeps indicate consumption (oxidation) of 12C-rich CH4 under suboxic conditions (probably utilizing readily available—up to 2000 μmol/l—Mn(IV)-oxihydroxides as electron acceptor). Thus, a combined diffusion–oxidation model was used to calculate methane fluxes of 0.3–393 kg/year across the brine–seawater boundary layer. Assuming steady-state conditions, this slow loss of methane from the brines into the Red Sea bottom water reflects a low thermogenic hydrocarbon input into the deep brines. 相似文献
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The oxygen isotope and trace element composition of hydrothermal quartz has been integrated with scanning electron microscope-cathodoluminescence (SEM-CL) images and fluid inclusion properties to track fluid sources and hydrothermal processes in the Mt. Leyshon Au deposit, Australia. Oxygen isotope and trace element data were collected on parallel traverses across the same quartz sections, using secondary isotope mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), respectively, with SEM-CL images obtained before analysis for petrographic context. Over the 280 to 650 °C quartz precipitation range suggested by fluid inclusion microthermometry, δ18Oquartz varies from 0.0 to 14.4‰, corresponding to a wide range of equilibrium δ18Ofluid values, from-6.1 to 10.2‰ (vs. V-SMOW). The δ18Oquartz signature varies systematically among distinct SEM-CL quartz generations (both within and between samples), and can be correlated with variations in temperature and fluid composition, but is independent of intra-generational oscillatory zoning. In contrast, Al and Li concentrations correlate broadly with CL intensity in oscillatory quartz, whereas their concentration is unpredictable in sealed fractures and overgrowths. Concentrations of B, Mg, Na, P, Cl, K, Ti, Mn, Fe, Ge, and Sn are independent of Al, Li, and oscillatory CL features, but Ti correlates with quartz precipitation temperature. Although no systematic correlation between δ18Oquartz and trace element concentrations was found, complementary patterns exist in narrow overgrowths of low δ18Oquartz ( 0‰) and high Al (> 10,000 ppma). These quartz zones likely formed during the incursion of 18O-depleted meteoric water into the magmatically-dominated Mt. Leyshon hydrothermal system. We interpret the highest Al concentrations as the result of high quartz precipitation rates, triggered by depressurisation of the hydrothermal cell. The decoupling of oxygen isotope and trace element patterns in quartz leads to the suggestion that (1) under most circumstances, temperature and fluid chemistry dominate δ18Oquartz, and (2) the trace element record, and in particular Al and Li, is influenced by the superimposed effects of quartz precipitation rate. 相似文献
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The production rate of 38Ar in meteorites—P(38)—has been determined, as a function of the sample's chemical composition, from 81Kr-Kr exposure ages of four eucrite falls. The cosmogenic 78Kr/83Kr ratio is used to estimate the shielding dependence of P(38).
From the “true” 38Ar exposure ages and the apparent 81Kr-Kr exposure ages of nine Antarctic eucrite finds, terrestrial ages are calculated. They range from about 3 × 105 a (Pecora Escarpment 82502) to very recent falls (Thiel Mountains 82502). Polymict eucrites from the Allan Hills (A78132, A79017 and A81009) have within the limits of error the same exposure age (15.2 × 106 a) and the same terrestrial age (1.1 × 105 a). This is taken as strong evidence that these meteorites are fragments of the same fall. A similar case are the Elephant Moraine polymict eucrites A79005, A79006 and 82600 with an exposure age of 26 × 106 a and a terrestrial age of 1.8 × 105 a. EETA79004 may be different from this group because its exposure age and terrestrial age are 21 × 106 a and 2.5 × 105 a, respectively.
The distribution of terrestrial ages of Allan Hills meteorites is discussed. Meteorites from this blue ice field have two sources: Directly deposited falls and meteorites transported to the Allan Hills inside the moving Antarctic ice sheet. During the surface residence time meteorites decompose due to weathering processes. The weathering “half-life” is about 1.6 × 105 a. From the different age distributions of Allan Hills and Yamato meteorites, it is concluded that meteorite concentrations of different Antarctic ice fields need different explanations. 相似文献
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Christian Bertoldi Alexander Proyer Dieter Garbe-Schnberg Harald Behrens Edgar Dachs 《Lithos》2004,78(4):389-409
Cordierite samples from pegmatites and metamorphic rocks have been analysed for major [electron microprobe analysis (EMPA)] and trace elements [inductively coupled plasma mass spectrometry (ICP-MS), secondary ion mass spectrometry analyses (SIMS)] as well as for H2O and CO2 (coulometric titration), and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant. Apart from the homovalent substitutions FeMg−1 and MnMg−1 on the octahedral site, some minor KNa−1 on the Ch0 channel site, and Fe3+Al−1 on the T11 tetrahedral site, the three most important substitution mechanisms are those for the incorporation of Li on the octahedral sites (NaLi□−1Mg−1), and of Be and other divalent cations on the tetrahedral T11 site (NaBe□−1Al−1 and Na(Mg,Fe2+)□−1Al−1). The dominant role of the last vector is clearly demonstrated. We propose a new generalized formula for cordierite: Ch(Na,K)0–1 VI(Mg,Fe2+,Mn,Li)2 IVSi5 IVAl3 IV(Al, Be, Mg, Fe2+, Fe3+)O18 *xCh(H2O, CO2…). Our results show that the population of (Mg, Fe2+) on the T11-site is limited to about 0.08 a.p.f.u. Other exchange mechanisms that were encountered in experiments operate only under P–T conditions or in bulk compositions that are rarely realized in nature. Routine analyses by electron microprobe in which Li and Be are not determined can be plotted as (Mg+Fe+Mn) versus (Si+Al) to assess whether significant amounts of Li and Be could be present. These amounts can be calculated as Li (a.p.f.u.)=Al+Na–4 and Be (a.p.f.u.)=10–2Al–M2+–Na. 相似文献
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The evolution of marine evaporitic brines in inland basins: The Jordan-Dead Sea Rift valley 总被引：1，自引：0，他引：1
Marine-evaporitic brines frequently display Na, Cl and Br concentrations that significantly deviate from seawater evaporation paths, yielding markedly conflicting degrees of evaporation calculated for a specific brine. Here we present 493 new and 33 previously reported analyses of Ca-chloridic waters of Neogene age from the Dead Sea Rift (DSR) valley to explain such offsets. The DSR brines plot along an almost perfect mixing line (R2 = 0.990) on a Br/Cl-Na/Cl diagram, extending between two end members A and B. Points A and B are located at Na/Cl = 0.804 and Br/Cl = 0.00193, and at Na/Cl = 0.00773 and Br/Cl = 0.0155, respectively, within the halite and bischofite stability fields.Brines A and B originated in a dual-mode evaporation basin. Brine A formed under the classic lagoon scenario (mode A), with seawater inflow and brine outflow at steady state. Occasional drops in water level, imposed by climatic or tectonic causes, resulted in outflow cutoff and in rapid concentration buildup. The second mode (B) initiated upon equilibration of the activity of water in the brine with the overlying relative humidity, resulting in composition and salinity approaching that of brine B, sustaining it until the next reversal to mode A.Thick evaporite deposits inhibited infiltration of brines A and B into the subsurface terrain, a process that was enabled only when the brine reached the permeable carbonate rock rim and border faults of the basin. Hence, brines that formed during the relatively short shifts from mode A to mode B could not penetrate into the deep subsurface, and bittern minerals that were formed during the frequent mode shifts were dissolved and flushed out into the sea upon the next resumption of outflow.The proposed model accounts for the deviations of brines from the marine evaporitic evolution curve by brine mixing, rather than due to a change in ocean chemistry. It also explains the absence of bittern minerals in the thick halite and gypsum/anhydrite succession, and the compositional gap between the widely different end member hypersaline fluids. This model applies directly to the studied DSR brines and evaporites, but it may be relevant to other inland evaporitic basins. 相似文献
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中国油页岩资源现状 总被引：59，自引：1，他引：58
2004～2006年我国首次开展了全国性油页岩资源评价工作。为了更好地揭示我国油页岩的分布规律及特征,按不同地区、不同层系、不同含油率、不同埋深和不同地理环境进行了归类汇总。评价结果表明,我国油页岩资源丰富,分布范围广,分布在20个省和自治区、47个盆地,共有80个含矿区。全国油页岩资源为7 199.37 亿t,页岩油资源为476.44 亿t,页岩油可回收资源为119.79 亿t。全国油页岩主要集中分布在东部区和中部区,东部区油页岩资源为3 442.48 亿t,中部区油页岩资源为1 609.64 亿t,青藏区油页岩资源为1 203.20 亿t,西部区油页岩资源为749.94 亿t,南方区油页岩资源为194.61 亿t,分别占全国油页岩资源的48％、22％、17％、10％和3％。全国油页岩主要集中分布在中、新生界,其中,中生界油页岩资源为5 597.92 亿t,新生界油页岩资源为1 052.31 亿t,分别占全国油页岩资源的77.76％和14.62％,油页岩形成时代从西北至东南方向逐渐变新。我国油页岩含油率中等偏好,其中含油率＞5％～10％的油页岩资源为2 664.35 亿t,含油率＞10％的油页岩资源为1 266.94 亿t,分别占全国油页岩资源的37％和18％。我国油页岩埋藏深度较浅,埋深在0～500 m之间的油页岩资源为4 663.51 亿t,埋深在500～1 000 m之间的油页岩资源为2 535.86 亿t,分别占全国油页岩资源的64.78％和35.22％。我国油页岩主要分布在平原和黄土塬地区,分布在平原地区的油页岩资源为3 256.53 亿t,分布于黄土塬地区的油页岩资源为1 562.86 亿t,分别占全国油页岩资源的45％和21％。油页岩资源巨大的盆地有:松辽盆地、鄂尔多斯盆地、准噶尔盆地,占全国油页岩资源的76.79％。 相似文献
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思茅盆地江城含盐带勐野井地区在“二层楼”钾盐成矿理论的指导下,逐步在侏罗系钾盐资源调查中取得重要成果,但盆地内其他含盐带研究程度薄弱。本文以整董含盐带的磨黑L2井勐野井组(K1m)盐岩样品为研究对象,通过显微镜观察、扫描电镜能谱分析、石盐矿物元素含量电子探针微区原位测试方法的建立,精细研究了样品岩相学、石盐矿物学及元素含量特征。同时,测试了江城含盐带勐野井地区MK-1井花开左组(J2h)石盐样品。对比研究两个井样品中石盐矿物微量元素K和Br含量及103Br/Cl值(质量分数比)特征,结合研究区地质演化,取得以下认识。L2井K1m(含)泥砾盐岩中石盐矿物发育两类产状:一类是胶结碎屑颗粒的主体石盐,具塑性流变特征;另一类是析出在碎屑中被盐类或黏土矿物碎屑包裹的石盐,两类包裹体特征指示均属次生成因。电子探针测得L2井K1m的主体石盐、碎屑包裹和勐野井MK-1井J2h含钾盐层石盐的K含量分别为≤0.09%、≤0.18%和≤0.13%,Br含量分别为≤60×10-6、70×10-6~410×10-6和70×10-6~500×10-6,103Br/Cl值分别为≤0.10、0.12~0.71和0.12~0.85,主体石盐显著低于后二者,处于陆源或海陆混合源石盐阶段或重结晶石盐阶段,而后二者数值接近,大多处在海源石盐阶段,小部分处在海源母液结晶钾石盐阶段和光卤石阶段。推断磨黑L2井碎屑包裹的石盐属深部古盐体刺穿贯入的证据,可能的成矿模式为深部中侏罗统海相古盐体受盐底辟作用迁移到浅层下白垩统勐野井组后,部分被盆地内侧向迁移来的中侏罗世残留海水、盆地周缘汇入的陆源水以及深部热液的共同溶蚀淋滤和混染改造形成新的卤水,部分以固体古石盐砾保留下来,在早白垩世晚期新母液卤水蒸发成盐过程中被形成的盐类和陆源碎屑矿物包裹,后期在母液结晶的主体石盐胶结下沉积成岩和成矿。以上认识完善了“二层楼”成矿理论在整董含盐带的勘探实践。 相似文献
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四川岷江上游叠溪发育有一套厚度超过200 m、保存较为完整的湖相沉积,被定名为叠溪古堰塞湖相沉积,其形成于距今30 ka前,存活了约15 ka,因此记录了青藏高原东缘晚更新世—全新世(包括末次冰期)的重大地质与环境事件。现有研究初步揭示了古堰塞的沉积特征,但对叠溪古滑坡及古堰塞湖形成与演化的系统研究还十分不足。本文通过详细的野外调查,结合现代遥感测绘技术(无人机载LiDAR),构建叠溪古滑坡的三维地质模型,研究了其地质与地貌特征。同时,采用高密度电阻率法ERT,在滑坡体上布设2条长870 m和990 m的测线,探明了滑坡体内部结构特征。通过古堰塞湖相沉积露头和钻孔的调查,结合激光粒度测试,重建了古堰塞湖的范围、规模与沉积特征。在此基础上,通过对古湖相沉积坡面上多级阶地的分析,初步探讨了古堰塞湖的消亡及其对下游史前古聚落变迁的影响。研究结果表明,叠溪古滑坡不仅完全堵塞岷江而且还堵塞了对岸支沟,堆积体方量达到(1 400~2 000)×106 m3。古堰塞湖在滑坡坝后向上游延伸26 km,所形成的最大湖面覆盖面积约21.4 km2,库容蓄水量约1 670×106 m3。叠溪古滑坡-堰塞湖在岷江上游形成了陡峭的河道裂点(Knickpoint),对山区河道与地貌演化具有长期影响。 相似文献
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S. R. Gí slason . Snorrason H. K. Kristmannsd ttir . E. Sveinbj rnsd ttir P. Torsander J.
lafsson S. Castet B. Dupr 《Chemical Geology》2002,190(1-4):181-205
The October 1996 eruption within the Vatnajökull Glacier, Iceland, provides a unique opportunity to study the net effect of volcanic eruptions on atmospheric and oceanic CO2. Volatile elements dissolved in the meltwater that enclosed the eruption site were eventually discharged into the ocean in a dramatic flood 35 days after the beginning of the eruption, enabling measurement of 50 dissolved element fluxes. The minimum concentration of exsolved CO2 in the 1×1012 kg of erupted magma was 516 mg/kg, S was 98 mg/kg, Cl was 14 mg/kg, and F was 2 mg/kg. The pH of the meltwater at the eruption site ranged from about 3 to 8. Volatile and dissolved element release to the meltwater in less than 35 days amounted to more than one million tonnes, equal to 0.1% of the mass of erupted magma. The total dissolved solid concentration in the floodwater was close to 500 mg/kg, pH ranged from 6.88 to 7.95, and suspended solid concentration ranged from 1% to 10%. According to H, O, C and S isotopes, most of the water was meteoric whereas the C and S were of magmatic origin. Both C and S went through isotopic fractionation due to precipitation at the eruption site, creating “short cuts” in their global cycles. The dissolved fluxes of C, Ca, Na, Si, S and Mg were greatest ranging from 1.4×1010 to 1.4×109 mol. The dissolved C flux equaled 0.6 million tonnes of CO2. The heavy metals Ni, Mn, Cu, Pb and Zn were relatively mobile during condensation and water–rock interactions at the eruption site. About half of the measured total carbon flood flux from the 1996 Vatnajökull eruption will be added to the long-term CO2 budget of the oceans and the atmosphere. The other half will eventually precipitate with the Ca and Mg released. Thus, for eruptions on the ocean floor, one can expect a net long-term C release to the ocean of less than half that of the exsolved gas. This is a considerably higher net C release than suggested for the oceanic crust by Staudigel et al. [Geochim. Cosmochim. Acta, 53 (1989) 3091]. In fact, they suggested a net loss of C. Therefore, magma degassed at the ocean floor contributes more C to the oceans and the atmosphere than magma degassed deep in the oceanic crust. The results of this study show that subglacial eruptions affecting the surface layer of the ocean where either Mn, Fe, Si or Cu are rate-determining for the growth of oceanic biomass have a potential for a transient net CO2 removal from the ocean and the atmosphere. For eruptions at high latitudes, timing is crucial for the effect of oceanic biota. Eruptions occurring in the wintertime when light is rate-determining for the growth of biota have much less potential for bringing about a transient net negative CO2 flux from the ocean atmosphere reservoir. 相似文献
15.
R. Braucher D. L. Bourls E. T. Brown F. Colin J. -P. Muller J. -J. Braun M. Delaune A. Edou Minko C. Lescouet G. M. Raisbeck F. Yiou 《Chemical Geology》2000,170(1-4):95-111
Depth profiles of in situ-produced cosmogenic nuclides, including 10Be (T1/2=1.5×106 years) and 26Al (T1/20.73×106 years), in the upper few meters of the Earth's crust may be used to study surficial processes, quantifying denudation and burial rates and elucidating mechanisms involved in landform evolution and soil formations. In this paper, we discuss the fundamentals of the method and apply it to two lateritic sequences located in African tropical forests. 相似文献
16.
济宁市是位于华北平原大气污染传输通道上的工业城市,为研究其秋、冬季细颗粒物(PM2.5)的污染特征,在市区的3个站点进行了PM2.5的同步滤膜采样。采样期为2018年10月15日至2019年1月31日,涵盖非采暖期和采暖期(自2019年11月15日始),共270个小流量滤膜样品。研究结果表明,济宁市秋、冬季PM2.5平均质量浓度为(98.9±48.8)μg/m3,采暖期PM2.5质量浓度(107.1±52.8)μg/m3显著高于非采暖期(77.4±27.8)μg/m3。PM2.5的化学组成以二次无机气溶胶、有机碳和元素碳为主,占比分别为52.4%、10.9%和7.5%。S、Cl、K、Ca、Fe和Si元素平均质量浓度之和占元素总平均质量浓度的78.8%,是PM2.5中的主要元素。采暖期PM2.5的主要化学组分质量浓度显著高于非采暖期。二次有机碳是有机碳的重要来源,占比78.9%。PM2.5中Zn和Pb的富集因子较高,说明燃煤及相关工业对PM2.5中重金属的贡献较为显著,ρ(NO3?)/ρ(SO42?)比值分析表明,济宁市整体受流动源影响较大。本研究可为查明华北平原典型工业城市的PM2.5污染来源成因提供依据。 相似文献
17.
R. B. Johns T. Belsky E. D. McCarthy A. L. Burlingame Pat Haug H. K. Schnoes W. Richter M. Calvin 《Geochimica et cosmochimica acta》1966,30(12):1191-1222
Several shales and oils ranging in age from 3 million to 2·7 billion years have been investigated for their hydrocarbon content using gas chromatography and mass spectrometry as primary analytical tools. From the Soudan Shale from Minnesota (2·7 × 109yr) the C18, C19, C20 and C21 isoprenoid-alkanes were obtained. The Antrim shale from Michigan (about 265 × 106 yr) yielded the C16, C18, C19, C20 and C21 isoprenoids, as well as a C16 iso-alkane and the C18 and C19 cyclohexyl n-alkanes. The San Joaquin Oil (30 × 106 yr) and the Abbott Rock Oil (3 × 106 yr) contained the C16, C18, C19, C20 and the C18, C19, C20 and C21 isoprenoids respectively. In addition, a series of iso-alkanes (C16−C18), anteiso-alkanes (C16−C18) and n-alkylcyclohexanes (C16−C19) as well as a C21 isoprenoid were obtained from the Nonesuch Seep Oil (1 × 109 yr). This analysis provides a comprehensive picture of the types of biogenic hydrocarbons found in oils and shales of widely differing ages, and in particular, the finding of isoprenoid alkanes in the Soudan Shale furnishes evidence for life processes at that period of geological time. 相似文献
18.
Flamingos,salt lakes and volcanoes: hunting for evidence of past climate change on the high Altiplano of Bolivia 
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下载免费PDF全文 Hidden within the vast Bolivian Altiplano are archives of past climate change in the form of remarkable carbonate rocks surrounding lakes long since disappeared. Beyond the Salar de Uyuni, the largest salt flat in the world, lies a relatively untouched realm of volcanoes and salt lakes. Ancient shorelines from intervals in the Altiplano history, when large lakes were more abundant, may hold important information about a time when the climate in this region was punctuated by much wetter phases before present day aridity took a hold. Previous studies in this region have reconstructed robust chronological timelines for such events and highlight two large lake phases over the last 18 thousand years (the Tauca and Coipasa lake phases); however higher resolution climate data are scarce. Current studies on climate proxies from smaller lakes in southern Bolivia may shed light on some of these higher resolution climate events including El Niño–Southern Oscillation (ENSO) events. Laminated tufa found around the palaeoshorelines of the West Lípez Lakes is one such proxy, and can be analysed to investigate the potential roles of annual versus shorter‐term climatic variation in the evolving Altiplano climate at the time. 相似文献
19.
Evaluation of boron isotopes in halite as an indicator of the salinity of Qarhan paleolake water in the eastern Qaidam Basin,western China 总被引：1，自引：0，他引：1
Yongsheng Du Qishun Fan Donglin Gao Haicheng Wei Fashou Shan Binkai Li Xiangru Zhang Qin Yuan Zhanjie Qin Qianhui Ren Xueming Teng 《地学前缘(英文版)》2019,10(1):253-262
In this study, nineteen brine samples from the Qarhan Salt Lake (QSL) in western China were collected and analyzed for boron (B) and chlorine (Cl) concentrations, total dissolved solids (TDS), pH values and stable B isotopic compositions. The B concentrations and δ11B values of brines in the QSL range from 51.6 mg/L to 138.4 mg/L, and from +9.32‰ to +13.08‰, respectively. By comparison of B concentrations and TDS of brines in QSL with evaporation paths of brackish water, we found that B enrichment of brines primarily results from strong evaporation and concentration of Qarhan lake water. Combining with comparisons of B concentrations, TDS, pH values and δ11B values of brines, previously elemental ratios (K/Cl, Mg/Cl, Ca/Cl, B/Cl) and δ11B values of halite from a sediment core (ISL1A), we observe good correlations between B concentrations and TDS, TDS and pH values, pH and δ11B values of brines, which demonstrate that higher B concentrations and more positive δ11B values of halite indicate higher salinity of the Qarhan paleolake water as well as drier paleoclimatic conditions. Based on this interpretation of the δ11B values of halite in core ISL1A, higher salinity of the Qarhan paleolake occurred during two intervals, around 46–34 ka and 26–9 ka, which are almost coincident with the upper and lower halite-dominated salt layers in core ISL1A, drier climate phases documented from the δ18O record of carbonate in core ISL1A and the paleomoisture record in monsoonal central Asia, and a higher solar insolation at 30°N. These results demonstrate that the δ11B values of halite in the arid Qaidam Basin could be regarded as a new proxy for reconstructing the salinity record of paleolake water as well as paleoclimate conditions. 相似文献
20.
The Canning Basin contains several Mississippi Valley‐type Zn‐Pb sulphide prospects and deposits in Devonian carbonate reef complexes on the northern edge of the Fitzroy Trough, and in Ordovician and Silurian marine sequences on the northern margin of the Willara Sub‐basin. This study uses the ionic composition and 5D, δ18O, δ34S, 87Sr/86Sr isotopic data on present‐day deep formation waters to determine their origin and possible relationship to the Zn‐Pb mineralizing palaeofluids. The present‐day Canning Basin formation waters have salinity ranging from typically less than 5000 mg/L up to 250 000 mg/L locally. The brines are mixtures of highly saline water, formed by seawater which evaporated beyond halite saturation (bittern water), with meteoric water ranging in salinity from low (<5000 mg/L) to hypersaline water (up to about 50 000 mg/L) formed by re‐solution of halite and calcium sulphate minerals. The original marine chemical composition of the bittern‐dominated brines was changed to that of a Na‐Ca‐Cl water by addition of Ca and removal of Mg and SO4, initially by bacterial sulphate reduction and later by dolomitization of carbonate. Other reactions with terrigenous components of the sediment have provided additional Ca and Sr, including a small proportion of 87Sr‐rich material. The δ34S values of the bittern‐containing waters are within the range over which marine sulphate has fluctuated from the Ordovician to the Holocene, although one of the hypersaline waters has a value of +6.8%, indicating SO4 of non‐marine origin. The pH of the bittern‐containing waters is low (about 5) and they contain significant concentrations of dissolved Fe (up to 120 mg/L). The Canning Basin bitterns appear similar in origin and chemical composition to highly saline marine brines in the Mississippi Salt Dome Basin, USA, which are known to be either metal or sulphide‐rich depending on the organic content of the host rock. In the Canning Basin, mixing of the bittern water with the various types of meteoric water has resulted in decreases in salinity, Na, Ca, Mg, K, Sr, Li and Fe, and increases in HCO3, SO4 and pH. Mixing of the bitterns with other types of metalliferous fluids and/or with sulphate‐containing hypersaline meteoric waters formed from the same marine evaporite sequence should produce ore‐precipitating fluids which are relatively hot and saline, and the resulting ore deposit should be of high grade and contain abundant sulphate minerals. In the southern Canning Basin, this type of mixing and the corresponding style of ore deposit is evident in the evaporite‐associated areas of Zn‐Pb mineralization near the Admiral Bay Fault. If the bitterns mix with low salinity HCO3‐waters in near‐surface environments, then the ore‐precipitating fluids should have relatively low salinities and carbonate minerals would precipitate during later stages of mixing. In the Lennard Shelf, the present‐day formation waters, the style of the Zn‐Pb deposits, and range of salinity and temperature of the ore‐forming palaeofluids are consistent with this type of mixing. 相似文献