首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 109 毫秒
1.
Artesian springs, which form carbonate mounds at the surface, occur in groups along the southwestern edge of the Great Artesian Basin (GAB), in northern South Australia. Their underground structure and relationship to faulting are not well understood. This study investigated four mound spring groups (Beresford Spring, Warburton Spring, the Bubbler Spring group, and Freeling Springs), which have different geological settings, using a range of geophysical techniques: self-potential (SP), magnetotellurics (MT) and time-domain electromagnetics (TEM). The results confirmed that despite generally similar mound morphologies at the surface, spring vents in different groups have different mechanisms for sourcing water from the GAB aquifer. SP measurements effectively showed where most of the vertical flow occurs at all groups, while MT and TEM models identified the location of faults, other geological structures and the thickness of the Bulldog Shale aquitard. Beresford and Warburton springs are similar in that the spring locations at both are directly related to points on a regional-scale fault, which appears to provide a low permeability pathway to the surface. At the Bubbler Springs group, a regionally aligned fault identified in MT data seems to be bounding an area where the aquifer is much closer to the surface (and the overlying aquitard has been thinned) where the spring abundance is highest. SP responses indicate that shallow flow paths feeding individual vents are unrelated to the fault. At Freeling Springs, the SP suggests that groundwater is flowing up within shallow aquifers, and that spring location is offset from this upward flow, instead located on range-front faults that provide the final conduit to the surface.  相似文献   

2.
Mound springs provide the primary discharge mechanism for waters of the western margin of the Great Artesian Basin (GAB), Australia. Though these springs are an important resource in an arid environment, their hydraulics as they discharge from shale are poorly defined. The springs can include extensive spring tails (groundwater-dependent wetlands) and hundreds of springs in a given spring complex. Electrical resistivity imaging (ERI) was used to evaluate spring subsurface hydraulic-connectivity characteristics at three spring complexes discharging through the Bulldog Shale. The results demonstrate that fresher GAB water appears as resistors in the subsurface at these sites, which are characterized by high-salinity conditions in the shallow subsurface. Using an empirical method developed for this work, the ERI data indicate that the spring complexes have multiple subsurface connections that are not always easily observed at the surface. The connections are focused along structural deformation in the shale allowing fluids to migrate through the confining unit. The ERI data suggest the carbonate deposits that the springs generate are deposited on top of the confining unit, not precipitated in the conduit. The data also suggest that spring-tail ecosystems are not the result of a single discharge point, but include secondary discharge points along the tail.  相似文献   

3.
Abstract

The Jurassic–Cretaceous Great Artesian Basin is the most extensive, and largest volume, sedimentary feature of continental Australia. The source of its mud-dominated Cretaceous infill is attributed largely to contemporary magmatism along the continental margin to the east, but the source of its Jurassic infill, dominated by quartz sandstone, remains unconstrained. This paper investigates the question of a Jurassic sediment source for the northern part of the basin. Jurassic uplift and exhumation of the continental margin crustal sector to the east provided the primary Jurassic sediment source. (U–Th)/He data are presented for zircon and apatite from Pennsylvanian to mid Permian granitoids of the Kennedy Igneous Association distributed within the northern Tasmanides between the Townsville and Cairns regions and for coeval granites of the Urannha batholith from the Mount Carlton district (N Bowen Basin), also within the northern Tasmanides. The data from zircon indicate widespread Jurassic exhumation of a crustal tract located to the east of the northern Great Artesian Basin and largely occupied by rocks of the Tasmanides. Detrital zircon age spectra for samples of the Jurassic Hutton and Blantyre sandstones from the northeastern margin of the Great Artesian Basin show their derivation to be largely from rocks of the northern Tasmanides. In combination, the detrital age spectra and (U–Th)/He data from zircon indicate exhumation owing to uplift generating appreciable physiographic relief along the north Queensland continental margin during the Jurassic, shedding sediment westward into the Great Artesian Basin during its early development. A portion of (U–Th)/He data for zircon are consistent with late Permian–mid Triassic exhumation within the Tasmanides, attributable to the influence of the Hunter--Bowen Orogeny. Evidence of Cretaceous and Paleocene exhumation episodes is also indicated for some samples, mainly by apatite (U–Th)/He analysis, consistent with data previously published from fission track studies. Overall, new data from the present study reveal that the exhumation related to Jurassic regional uplift and the subsequent erosional reworking of the northeast Australian continental margin is critical for the evolution and development of the northern side of the Great Artesian Basin in eastern Australia. Apart from this, another two previously suggested Permian–Triassic and Cretaceous exhumation and uplift episodes along the northeast Australian continental margin are also confirmed by the dataset of this study.
  1. KEY POINTS

  2. U–Pb detrital zircon ages of sandstone samples from the northeastern Eromanga Basin reveal Paleozoic (480–280 Ma) and Proterozoic (1800–1400 Ma) age clusters.

  3. (U–Th)/He zircon and apatite dating results of granitoids samples from Cairns, Townsville and the Mount Carlton districts are dominated by Jurassic (198–164 Ma) and Permian–Triassic (272–238 Ma) age clusters.

  4. Combination of above two datasets proves the regional uplift-driving Jurassic exhumation episode in the northeast Australian continental is vital for the development of the northern Great Artesian Basin.

  相似文献   

4.
Several natural and anthropogenic tracers have been used to evaluate groundwater residence time within a karstic limestone aquifer in southeastern New Mexico, USA. Natural groundwater discharge occurs in the lower Pecos Valley from a region of karst springs, wetlands and sinkhole lakes at Bitter Lakes National Wildlife Refuge, on the northeast margin of the Roswell Artesian Basin. The springs and sinkholes are formed in gypsum bedrock that serves as a leaky confining unit for an artesian aquifer in the underlying San Andres limestone. Because wetlands on the Refuge provide habitat for threatened and endangered species, there is concern about the potential for contamination by anthropogenic activity in the aquifer recharge area. Estimates of the time required for groundwater to travel through the artesian aquifer vary widely because of uncertainties regarding karst conduit flow. A better understanding of groundwater residence time is required to make informed decisions about management of water resources and wildlife habitat at Bitter Lakes. Results indicate that the artesian aquifer contains a significant component of water recharged within the last 10–50 years, combined with pre-modern groundwater originating from deeper underlying aquifers, some of which may be indirectly sourced from the high Sacramento Mountains to the west.  相似文献   

5.
The investigation of regionally extensive groundwater systems in remote areas is hindered by a shortage of data due to a sparse observation network, which limits our understanding of the hydrogeological processes in arid regions. The study used a multidisciplinary approach to determine hydraulic connectivity between the Great Artesian Basin (GAB) and the underlying Arckaringa Basin in the desert region of Central Australia. In order to manage the impacts of groundwater abstraction from the Arckaringa Basin, it is vital to understand its connectivity with the GAB (upper aquifer), as the latter supports local pastoral stations and groundwater-dependent springs with unique endemic flora and fauna. The study is based on the collation of available geological information, a detailed analysis of hydraulic data, and data on environmental tracers. Enhanced inter-aquifer leakage in the centre of the study area was identified, as well as recharge to the GAB from ephemeral rivers and waterholes. Throughout the rest of the study area, inter-aquifer leakage is likely controlled by diffuse inter-aquifer leakage, but the coarse spatial resolution means that the presence of additional enhanced inter-aquifer leakage sites cannot be excluded. This study makes the case that a multi-tracer approach along with groundwater hydraulics and geology provides a tool-set to investigate enhanced inter-aquifer leakage even in a groundwater basin with a paucity of data. A particular problem encountered in this study was the ambiguous interpretation of different age tracers, which is attributed to diffusive transport across flow paths caused by low recharge rates.  相似文献   

6.
Historical groundwater levels in a coastal region of Hong Kong Island (China) were reviewed and compared with data collected recently to reveal changes to the groundwater regime over the last century. The coastal springs and seeps have disappeared and the lower boundary of the seepage zone has moved uphill. Groundwater was found to be flowing upward along the boundary of natural slopes and urbanized areas. Artesian flows were commonly noted in the deep piezometers in the lower urbanized areas. Moreover, an overall rise in water levels in a 10-year period was observed in the urbanized areas, except in areas with good drainage. Extensive urbanization since the 1950s has included large-scale land reclamation, deep foundations of high-rise buildings, an underground transport system, water mains and horizontal drains in slopes; the effect has been a slow but gradual increase in the water level of the hillslope groundwater system. Further urbanization activities such as the westward extension of the underground transport system and new major drainage systems in the slopes, should be assessed for possible further changes to the groundwater system. The results presented here may serve as reference for other highly-urbanized coastal areas in the world.  相似文献   

7.
海原盆地地下水咸化特征和控制因素   总被引：1，自引：0，他引：1       下载免费PDF全文
地下水是海原盆地唯一的供水水源,近年来部分地区地下水溶解性总固体(TDS)增高,引起了有关部门和水文地质工作者的高度关注。通过分析69组地下水样品的水化学和氢氧稳定同位素数据,对地下水补给来源和咸化的水文地球化学过程进行了研究。结果表明:地下水TDS值198.2~6 436.4 mg/L,沿着地下水流向,咸化程度增加,水化学类型从基岩区的HCO3—Ca·Mg型演化至滞留—排泄区的SO4·Cl—Na·Mg型。地下水补给来源主要为大气降雨和基岩裂隙水侧向径流,补给源—对地下水咸化贡献较小。溶滤作用具空间差异,基岩区和补给区以碳酸盐、硅酸盐风化为主,径流区和滞留—排泄区则为蒸发岩风化,硫酸盐是地下水中阳离子的主要来源。补给水、溶滤和蒸发对第四系地下水TDS的贡献比率分别为4.8%~81.2%、11.9% ~85.9%、1.7%~29.5%,溶滤作用是控制海原盆地地下水咸化的首要因素。当地有关部门应加大对基岩泉水的综合利用,同时注意控制海原县和西安镇等地区地下水开采量,防止地下水进一步咸化。另外,在微咸水分布区可引进地下水去除硫酸盐技术,提高微咸水利用程度。  相似文献   

8.
The effectiveness of carbon capture and geologic storage depends on many factors, including and especially the permeability of the reservoir’s caprock. While caprock integrity is generally assumed if petroleum has been preserved, it is poorly constrained in reservoirs containing only saline waters, and CO2 leakage poses a potential risk to shallow aquifers. Naturally-occurring He accumulates in pore waters over time with the concentration being strongly dependent on the long term flux of fluid through the caprock. Furthermore, a small fraction of pore-water He diffuses into quartz and this may be used as a proxy for He concentrations in pore water, where dissolved gas samples are difficult to obtain, such as in deep sedimentary basins. In this paper He contained in quartz grains is measured and compared to previously measured pore water concentrations. Quartz was purified from core samples from the San Juan Basin, New Mexico and the Great Artesian Basin, South Australia. Quartz separates were heated at 290 °C to release He from the quartz. The quartz from the San Juan Basin and high purity quartz from the Spruce Pine Intrusion, North Carolina was repeatedly impregnated at varying pressures using pure He, heated and analyzed to build He sorption isotherms. The isotherms appear linear but vary between samples, possibly due to fluid inclusions within the quartz grains as high purity quartz samples partition only 1.5% of He that partitions into San Juan Basin samples. Concentrations of He in the pore water were calculated using the He-accessible volume of the quartz and the air–water He solubility. The mean San Juan Basin He pore water concentration was 2 × 10–5 cc STP He/g water, ∼400 times greater than atmospheric solubility. Great Artesian Basin samples contain a mean He concentration of 3 × 10–6 cc STP He/g water or 65 times greater than atmospheric solubility. However, pore water He concentrations in both the San Juan and Great Artesian Basins differ by up to an order of magnitude compared to samples collected with an alternate method. The reason for the offset is attributable to either partial saturation of the pore volume or a lack of He equilibrium between quartz and pore water. Coating of clay or other mineral phases on quartz grains, which tends to reduce the effective diffusion coefficient, may cause the latter. This technique of assessing permeability is promising due to the abundance of existing core samples from numerous basins where carbon sequestration may ultimately occur.  相似文献   

9.
Despite its extreme aridity, the Ordos Basin in northern China is rich in groundwater. Many artesian wells or springs with large fluxes are utilized for drinking, irrigation and industrial production. In a search for the origin of the groundwater, a detailed investigation of the stable isotopes of oxygen and hydrogen in the local precipitation, the river water, the springs, the well water, as well as the soil water extracted from six soil profiles in the Ordos Basin, was carried out. The data show that δD, δ18O and TDS values of the river water are similar to those of groundwater, while the TDS values of the soil water are about ten times greater than those of groundwater. Furthermore, the mean isotopic compositions of the local precipitation are significantly higher than those of river water and groundwater. Based on the chloride mass balance method, the estimated recharge rates range from 5.2 to 17.2 mm/year, with a mean value of 10.5 mm/year. The results show that the main source of recharge of the groundwater in the Ordos Basin is not the local precipitation, but must come from a region where the precipitation is characterized by much lower δD and δ18O values. In addition, the groundwater in the Ordos Basin contains a component of mantle-derived 3He and crust-derived 4He suggesting that the groundwater may partly derive from flows through basement faults beneath the Ordos Basin.  相似文献   

10.
Coal-seam gas production requires groundwater extraction from coal-bearing formations to reduce the hydraulic pressure and improve gas recovery. In layered sedimentary basins, the coalbeds are often separated from freshwater aquifers by low-permeability aquitards. However, hydraulic connection between the coalbed and aquifers is possible due to the heterogeneity in the aquitard such as the existence of conductive faults or sandy channel deposits. For coal-seam gas extraction operations, it is desirable to identify areas in a basin where the probability of hydraulic connection between the coalbed and aquifers is low in order to avoid unnecessary loss of groundwater from aquifers and gas production problems. A connection indicator, the groundwater age indictor (GAI), is proposed, to quantify the degree of hydraulic connection. The spatial distribution of GAI can indicate the optimum positions for gas/water extraction in the coalbed. Depressurizing the coalbed at locations with a low GAI would result in little or no interaction with the aquifer when compared to the other positions. The concept of GAI is validated on synthetic cases and is then applied to the north Galilee Basin, Australia, to assess the degree of hydraulic connection between the Aramac Coal Measure and the water-bearing formations in the Great Artesian Basin, which are separated by an aquitard, the Betts Creek Beds. It is found that the GAI is higher in the western part of the basin, indicating a higher risk to depressurization of the coalbed in this region due to the strong hydraulic connection between the coalbed and the overlying aquifer.  相似文献   

11.
The geochemical evolution of groundwater in the Ordovician-Cambrian aquifer system in the northern part of the Baltic Artesian Basin (BAB) illustrates how continental glaciations have influenced groundwater systems in proglacial areas. The aquifer system contains water that has originated from various end-members: recent meteoric water, glacial meltwater and relict Na-Cl brine. The saline formation water that occupied the aquifer system prior to the glacial meltwater intrusion has been diluted by meltwaters of advancing-retreating ice sheets. The diversity in the origin of groundwater in the aquifer system is illustrated by a wide variety in δ18O values that range from −11‰ to −22.5‰. These values are mostly depleted with respect to values found in modern precipitation in the area. The chemical and isotopic composition of groundwater has been influenced by mixing between waters originating from different end-members. In addition, the freshening of a previously saline water aquifer due to glacial meltwater intrusion has initiated various types of water-rock interaction (e.g. ion exchange, carbonate mineral dissolution).  相似文献   

12.
鄂尔多斯白垩系地下水盆地地下水水化学类型的分布规律   总被引：10，自引：0，他引：10  
在对鄂尔多斯白垩系地下水盆地1 125件地下水化学样品进行分析的基础上,总结出研究区不同循环深度地下水化学类型的分布规律。总体上,盆地北区大致以安边—四十里梁—东胜梁地表分水岭为界,东侧地区的浅层、中层和深层地下水化学类型均以HCO3型水为主,地下水水平分带不典型;而分水岭以西的摩林河－盐海子地下水系统和都思兔河—盐池地下水系统中,包括浅层、中层和深层在内的各层地下水表现为沿地下水流向,向盆地北、西侧边界,水化学类型具有明显的水平分带规律。而盆地南区地下水分层径流明显,水化学类型复杂,总体上存在一个以定边—环县—合水—华池—吴旗—定边为中心的北部由北向南、东部由东向西、南部由西南向东北的水平分带。  相似文献   

13.
受深切河谷地貌控制,黔东北大部分地区岩溶地下水深埋且排泄于河谷岸边,以快速的管道裂隙流为主,给地下水资源勘探开发带来了极大的困难,局部地区受蓄水构造控制形成勘探有利的地下水富集区。笔者基于地貌和蓄水构造将研究区岩溶地下水系统归纳总结为深切河谷型、向斜山地型、单斜夹层型和背斜槽谷型4类模式。深切河谷型岩溶地下水系统地下水水力坡度大,地下水以快速的管道流为主,排泄点低,开发利用方式建议直接在地下河出口或天窗中抽提地下水,经济效益明显地区可堵洞成库进行综合利用;向斜山地型岩溶地下水系统发育高位岩溶泉或地下河出口,排泄点高,适合直接引水利用;单斜夹层型岩溶地下水系统在岩性接触带出露一系列接触泉,排泄分散,开发利用方式建议直接利用或抽提岩溶泉水,受夹层隔水顶底板影响局部地区可钻井取水;背斜核部出露寒武系白云岩地层,导致背斜槽谷型岩溶地下水系统含水岩层均匀厚度大,分布大量非全排型岩溶泉,地下水开发适合抽提泉水或钻井抽取地下水。  相似文献   

14.
拒马源泉群作为拒马河的源头,受到了较多专家和学者的关注。但这些研究多集中在地下水的水化学、水位动态、泉流量等特征上,对地下水氢氧同位素特征的分析几乎没有,且对北海泉的成因解释多为粗略的定性概述。为了说明涞源北盆地地下水的氢氧同位素特征,详细揭示北海泉的形成模式,首次系统地采集了不同含水岩组的地下水样品,测定了水样的氢氧同位素组分。结果表明:样品点δD和δ18O值均落在区域大气降水线上或附近,大气降水是研究区地下水的主要补给来源;白云岩、灰岩含水岩组高程效应较明显,径流途径长,松散含水层径流途径短,受蒸发作用较强;白云岩、灰岩含水岩组和松散含水层氘盈余d值分别为6.0‰～11.6‰、4.2‰～11.2‰、3.8‰～8.0‰,较大气降水大部分偏小,表明岩溶水和松散孔隙水经历了不同的流动过程;白云岩、灰岩含水岩组从补给区向排泄区各自流动过程中,在小西庄、香炉屯村附近断裂带发生沟通混合,然后在向盆地中心径流过程中受断层阻水上升,上升过程中又接受了松散孔隙水的补给,最后在松散岩层中出露成泉,形成北海泉。在孔隙水混入前,两者的平均补给比例大约为48.4%～57.6%和42.4%～51.6%。  相似文献   

15.
Analysis of geothermal and hydrogeologic characteristics of Paleozoic interior basins of Brazil has identified an association between the geographic distribution of thermal springs and areas of occurrences of groundwater flow. Specifically, thermal springs are found to be absent in regions inferred to have lateral flows of groundwater. This trend is evident in the basins of the Amazon region, in the central parts of the Parnaíba basin and in the west-central parts of the Paraná basin. Model studies help to elucidate mutual exclusion of regions of thermal springs and sub-horizontal flows of groundwater. Numerical simulations indicate that groundwater flows with velocities ≥ 1 cm/year are capable of masking the occurrence of thermal anomalies. Also, down flow through distributed recharge zones can lead to development of large zones of relatively low temperature. The observational data sets of temperature gradients and Peclet numbers have been employed outlining advection-convection domains of subsurface strata in the sedimentary basins of the Amazon region, Parnaíba and Paraná. Results obtained indicate that thermal buoyancy forces are incapable of overcoming advective flows in basins of the Amazon region. Similar conditions are also found to prevail in the central parts of the Parnaíba and Paraná basins.  相似文献   

16.
Stable Cl isotope ratios (37Cl/35Cl) were measured in groundwater samples from the southwestern flow system of the Great Artesian Basin, Australia to gain a better understanding of the Cl− sources and transport mechanisms. δ37Cl values range from 0‰ to −2.5‰ (SMOC), and are inversely correlated with Cl− concentration along the inferred flow direction. The Cl isotopic compositions, in conjunction with other geochemical parameters, suggest that Cl− in groundwaters is not derived from salt dissolution. Mixing of the recharge water with saline groundwater cannot explain the relationship between δ37Cl and Cl− concentration measured. Marine aerosols deposited via rainfall and subsequent evapotranspiration appear to be responsible for the Cl− concentrations observed in wells that are close to the recharge area, and in groundwaters sampled along the southern transect. δ37Cl values measured in the leachate of the Bulldog shale suggest that the aquitard is the subsurface source of Cl− for the majority of groundwater samples studied. Diffusion is likely the mechanism through which Cl− is transported from the pore water of the Bulldog shale to the aquifer. However, a more detailed study of the aquitard rocks is required to verify this hypothesis.  相似文献   

17.
晋西南峨嵋台塬的岩溶水系统及岩溶水资源潜力   总被引：1，自引：0，他引：1  
本文通过分析峨嵋台塬的地质结构和岩溶水补给的自然条件,提出:(1)峨嵋台塬岩溶水具独立的地下水系统特征,北边界为里望断裂,南边界为临猗断裂,西边界为沿黄河东岸延展的夹马口—小梁断裂,东边界为稷王山东麓泥页岩带和变质岩体;(2)岩溶水主要来自稷王山裸露区大气降水,少量排向河津—侯马盆地和运城盆地,大量沿临猗断裂带向黄河方向迳流排泄,排泄量不到东王岩溶泉流量的10%;(3)峨嵋台塬岩溶水潜力有限。  相似文献   

18.
The lithium isotopic composition of waters of the Mono Basin, California   总被引：2，自引：0，他引：2  
Mono Lake, a major closed-basin alkaline salt lake in eastern California, derives its water from a mixture of creeks and springs, with the former providing in excess of 75% of the total. The Li isotopic composition of lake water has not varied significantly over a 4 year meromictic period (δ7Li ∼ +19.5). Springs are isotopically distinct: groundwater springs and seeps carry water enriched in isotopically heavy Li whereas thermal springs supply isotopically light (δ7Li < lake), but 10 times more Li-rich, water. Isotopic fractionation during crystallization of carbonate tufa and evaporitic salt appears to be insignificant, and thus cannot be called on as a principal control of the isotopic balance of Li of the lake. Isotopic differences between the end-member source components permit a water budget to be calculated, suggesting (1) springs provide > 50% of the Li to the lake; (2) the Li budget is sensitively balanced on small thermal spring contributions, < 3% of the total spring inflow; and (3) the residence time of Li in the lake is 28 ka. Other Great Basin closed lakes have variable Li isotopic compositions (δ7Li from +16.7 to +23.7), all of which differ significantly from those of several major lakes and seawater (homogeneously ∼ +32).  相似文献   

19.
The Latrobe aquifer in the Gippsland Basin in southeastern Australia is a prime example for emerging resource conflicts in Australian sedimentary basins. The Latrobe Group forms a major freshwater aquifer in the onshore Gippsland Basin, and is an important reservoir for oil and gas in both onshore and offshore parts of the basin. The Latrobe Group and overlying formations contain substantial coal resources that are being mined in the onshore part of the basin. These may have coal-seam-gas potential and, in addition, the basin is considered prospective for its geothermal energy and CO2 storage potential. The impacts of groundwater extraction related to coal-mine dewatering, public water supply, and petroleum production on the flow of variable-density formation water has been assessed using freshwater hydraulic heads and impelling force vectors. Groundwater flows from the northern and western edges towards the central part of the basin. Groundwater discharge occurs mainly offshore along the southern margin. Post-stress hydraulic heads show significant declines near the petroleum fields and in the coal mining areas. A hydrodynamic model of the Latrobe aquifer was used to simulate groundwater recovery in the Latrobe aquifer from different scenarios of cessation of groundwater and other fluid extractions.  相似文献   

20.
The means and timing of the formation of Australian sediment-hosted precious opal remain a subject of continuing debate. In this study, the question of which water formed the opal is addressed by examination of rare earth element data for opals and host rocks. The available data, mainly for Lightning Ridge, NSW, suggest a positive Eu anomaly, relative to the neighbouring Sm and Dy, occurs in opals whereas no such anomaly was found for the weathered Cretaceous sediments hosting the opal. Such anomalies may be inherited from the source rock with a similar positive Eu anomaly or generated in situ by severe reduction. There is no indication of major reduction processes during the opal formation that could have led to such a Eu anomaly so this is likely inherited from a source rock. As the opal host rocks did not show this anomaly, the source rocks must be external to the opal fields. Calcite cements within rocks hosting the aquifers of the Eromanga and Surat basins of the Great Artesian Basin have been reported to have a positive Eu anomaly, which strongly suggests that opal was formed by upwelling Great Artesian Basin artesian waters. This work has also highlighted variations in trace-element concentrations in opals, which indicate significant variation in the source water composition during opal formation or different water sources were involved. Either of these is indicative of the source for the opal with its trace elements derived from external sources. These conclusions have significant implications to considerations of how opal formed, and hence, for the exploration for other deposits and to the chemistry and timing that led to the formation of opal.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号