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1.
《Applied Geochemistry》1997,12(2):213-224
In March 1994, soil gases were sampled in the area of Vulcano Porto, on the island of Vulcano, using a grid of about 200 points/km2. Analysed gases were CO2, He and222Rn and, over a smaller area, H2S. Some of the samples were also analysed for the isotope composition of CO2C. Three anomalous CO2 degassing areas were identified: Grotta dei Palizzi, the area near the Telephone Exchange, and the area near the beach fumaroles. The behaviour of He and222Rn is different in these 3 areas. The concentration of He is much lower than that of atmospheric He (down to −3950 ppb) in the isthmus, and only in the area near Grotta dei Palizzi does it have values significantly higher than atmospheric ones (up to 1900 ppb). The activity of222Rn, always significantly positively related to CO2 concentrations, peaked in the 2 fumarole areas (isthmus, Telephone Exchange). 相似文献
2.
地震活动断裂带能够向大气释放大量的温室气体、放射性气体和有毒气体(CO_2、CH_4、Rn和Hg),并对大气环境的影响产生复杂的影响。利用静态暗箱法,对汶川M_s8.0地震破裂带CO_2、Rn和Hg脱气强度进行实地测量,并计算了CO_2和Hg脱气对大气的年贡献量。结果表明:(1)破裂带土壤气中CO_2、CH_4、Rn和Hg异常浓度最大值分别可以达到7.98%、2.38%、524.30k Bq/m~3和161.00ng/m~3;破裂带CO_2、Rn和Hg脱气平均通量是34.95g·m~(-2)d~(-1)、36.11m Bq·m~(-2)s~(-1)和26.56ng·m~(-2)h~(-1),最大值分别达到259.23g·m~(-2)d~(-1)、580.35m Bq·m~(-2)s~(-1)和387.67ng·m~(-2)h~(-1);(2)汶川Ms8.0地震破裂带向大气脱气的CO_2年贡献量是0.95Mt,Hg的年贡献量是15.94kg。汶川Ms8.0地震破裂带破裂CO_2、CH_4、Rn和Hg等的脱气强度,不仅与破裂带渗透率有关,还与断裂带浅部存在的气藏、煤层以及磷矿层等气体源有重要的联系。 相似文献
3.
Luisa Stellato Emma Petrella Filippo Terrasi Paolo Belloni Maria Belli Umberto Sansone Fulvio Celico 《Hydrogeology Journal》2008,16(4):701-712
222Rn was used to assess river–groundwater interactions within Castel di Sangro alluvial aquifer (Italy). The effectiveness of results obtained through this indicator was verified by also analyzing δ18O, major ions and temperature in both surface and groundwater, and carrying out piezometric head monitoring and discharge measurements. Hydrogeological investigations suggested that the river infiltrates into the aquifer in the south-eastern aquifer portion, while groundwater discharges into the river in the north-eastern portion. The latter phenomenon is supported by 222Rn data. Nevertheless, flow-through conditions cause the modelled discharge along this river reach, estimated by 222Rn data in a degassing-corrected two-component mixing model, to be greater than the measured discharge. Concerning river infiltration into the aquifer, δ18O, major ions and temperature data show that the river contribution is negligible in terms of aquifer recharge. Thus, the observed increase in 222Rn concentration in that portion of the aquifer is due to the enrichment process caused by infiltration of rainwater (222Rn free) which flows from the local divide area. Hence, in the study site, the use of only 222Rn to predict river–groundwater interactions causes some estimation inaccuracies and it must be coupled with other hydrochemical and hydrogeological parameters to gain a thorough understanding of such interactions. 相似文献
4.
A geochemical survey, in shallow aquifers and soils, has been carried out to evaluate the feasibility of natural gas (CH4) storage in a deep saline aquifer at Rivara (MO), Northern Italy. This paper discusses the areal distribution of CO2 and CH4 fluxes and CO2, CH4, Rn, He, H2 concentrations both in soils and shallow aquifers above the proposed storage reservoir. The distribution of pathfinder elements such as 222Rn, He and H2 has been studied in order to identify potential faults and/or fractures related to preferential migration pathways and the possible interactions between the reservoir and surface. A geochemical and isotopic characterization of the ground waters circulating in the first 200 m has allowed to investigation of (i) the origin of the circulating fluids, (ii) the gas–water–rock interaction processes, (iii) the amount of dissolved gases and/or their saturation status. In the first 200 m, the presence of CH4-rich reducing waters are probably related to organic matter (peat) bearing strata which generate shallow-derived CH4, as elsewhere in the Po Plain. On the basis of isotopic analysis, no hints of thermogenic CH4 gas leakage from a deeper reservoir have been shown. The δ13C(CO2) both in ground waters and free gases suggests a prevalent shallow origin of CO2 (i.e. organic and/or soil-derived). The acquisition of pre-injection data is strategic for the natural gas storage development project and as a baseline for future monitoring during the gas injection/withdrawing period. Such a geochemical approach is considered as a methodological reference model for future CO2/CH4 storage projects. 相似文献
5.
Many water-supply systems in South America utilize the waters of the Guarani aquifer at least as part of their networks. However, there is little present knowledge in Brazil of the factors affecting Rn presence in the water supplied for end-users, despite the economic importance of Guarani aquifer. 222Rn analyzes of 162 water samples were performed at 8 municipalities in São Paulo State, Brazil, with the aim of investigating the major factors affecting its presence in solution. The 222Rn activity concentration ranged from 0.04 up to 204.9 Bq/L, with three samples exceeding the World Health Organization maximum limit of 100 Bq/L. Aeration was confirmed as the most important factor for Rn release, as expected due to its gaseous nature. Accumulation in pipes and stratification in the water column were other significant factors explaining the data obtained in some circumstances. The Rn daughters 214Pb and 214Bi were also determined in a set of selected samples and their presence was directly related to the occurrence of Rn dissolved in water. 相似文献
6.
The radon-222 (222Rn) activity in groundwater of the Apulian karstic aquifer in southern Italy is as great as 500 Becquerel per liter (Bq/L)
locally. Normal radium-226 (226Ra) activity in the limestone and calcareous dolomites of the aquifer is not enough to explain such a high level. Laboratory
investigations identified high 226Ra activity in the "terra rossa," the residuum occupying fissures and cavities in the bedrock, and also the relation between
(1) 226Ra-bearing bedrock and "terra rossa" and (2) 222Rn in water. The "terra rossa" is the primary source of the radon in the groundwater. The experimental results show the need
to characterize the "terra rossa" of Apulia on the basis of 226Ra activity and also to study the distribution and variations in 222Rn activity over time in the aquifer.
Received, January 1996 · Revised, March 1997, September 1997, June 1998 · Accepted, July 1998 相似文献
7.
Integrated geophysics and soil gas profiles as a tool to characterize active faults: the Amer fault example (Pyrenees, NE Spain) 总被引：1，自引：0，他引：1
M. Zarroca R. Linares J. Bach C. Roqué V. Moreno Ll. Font C. Baixeras 《Environmental Earth Sciences》2012,67(3):889-910
The combined use of geophysical and soil gas composition exploration methods allows to rapidly obtain at relative low cost information that might be related to seismic activity conditions. In this study, we carried out geochemical soil gas sampling (222Rn, 220Rn and CO2), electrical resistivity tomography and seismic refraction profiles in two selected zones near the town of Amer in the Spanish Pyrenees, where the presence of recent fractures is evident in the field. Data analysis clearly reveals anomalous values for each gas at specific positions along the electrical imaging transects. Geomorphologic and hydrogeologic data and the integration of geophysical data and soil gas measurements indicate that: (1) endogene gases radon (222Rn) and carbon dioxide (CO2) are released from the meta-sedimentary basement rocks across the main fractured zones with higher permeability values, while lower Cenozoic detrital sedimentary formations act as an impervious boundary; (2) sites with highest radon concentrations (52?kBq?m?3) coincide with the zones in the Amer fault showing more recent geomorphic evidence of activity, and more specifically with those areas covered by thinner surficial formations; (3) the lowest 222Rn values (0.2?C0.4?kBq?m?3) were recorded just on the master active fault plane. This pattern could be explained by a dilution effect resulting from high rates of soil CO2 efflux (267?g?m?2?day?1); (4) soil thoron (220Rn) activity is maximum (143?kBq?m?3) in areas with high surficial fracturing; (5) groundwater pumping may cause important distortions in the natural flow dynamics and in the measured concentrations of gases. The agreement between the different data (geochemical, geophysical, and hydrogeological) and field observations (geology and geomorphology) leads us to propose a preliminary tectonic-gravitational model for the study area. 相似文献
8.
Analysis of the exchange of groundwater and river water by using Radon-222 in the middle Heihe Basin of northwestern China 总被引：9，自引：1，他引：8
In arid regions of western China, water resources come from mountain watersheds and disappear in the desert plain. The exchange of surface water and groundwater takes place two or three times in a basin. It is essential to analyze the interaction of groundwater with surface water to use water resources effectively and predict the change in the water environment. The conventional method of analysis, however, measures only the flow of a stream and cannot determine groundwater seepage accurately. As the concentration of Radon-222 (222Rn) in groundwater is much higher than in surface water, the use of 222Rn was examined as an indicator for the analysis of the interaction between surface water and groundwater. Measurement of the 222Rn concentration in surface water was conducted to detect groundwater seepage into a stream in the middle Heihe Basin of northwestern China. Furthermore, the simultaneous groundwater flow into and out of a stream from the aquifers was quantified by solving the 222Rn mass balance equation, in which the losses of gas exchange and radioactive decay of 222Rn are considered. Meanwhile, river runoff was gauged to determine the exchange rates between surface water and groundwater. The result shows that 222Rn isotope can be used as a good environmental tracer with high sensitivity for the interaction between surface water and groundwater, especially in the fractured aquifer system, karst aquifer system and discharge basins. 相似文献
9.
A model for the groundwater transport of naturally occurring U, Th, Ra, and Rn nuclides in the238U and232Th decay series is discussed. The model developed here takes into account transport by advection and the physico-chemical
processes of weathering, decay, α-recoil, and sorption at the water-rock interface. It describes the evolution along a flowline
of the activities of the238U and232Th decay series nuclides in groundwater. Simple sets of relationships governing the activities of the various species in solution
are derived, and these can be used both to calculate effective retardation factors and to interpret groundwater data. For
the activities of each nuclide, a general solution to the transport equation has been obtained, which shows that the activities
reach a constant value after a distance ϰi, characteristic of each nuclide. Where ϰi is much longer than the aquifer length, (for238U,234U, and232Th), the activities grow linearly with distance. Where gKi is short compared to the aquifer length, (for234Th,230Th,228Th,228Ra, and224Ra), the activities rapidly reach a constant or quasi-constant activity value. For226Ra and222Rn, the limiting activity is reached after 1 km.
High δ234U values (proportional to the ratioɛ234Th/W238U) can be obtained through high recoil fraction and/or low weathering rates. The activity ratios230Th/232Th,228Ra/226Ra and224Ra/226Ra have been considered in the cases where either weathering or recoil is the predominant process of input from the mineral
grain. Typical values for weathering rates and recoil fractions for a sandy aquifer indicate that recoil is the dominant process
for Th isotopic ratios in the water. Measured data for Ra isotope activity ratios indicate that recoil is the process generally
controlling the Ra isotopic composition in water. Higher isotopic ratios can be explained by different desorption kinetics
of Ra. However, the model does not provide an explanation for228Ra/226Ra and224Ra/226Ra activity ratios less than unity.
From the model, the highest222Rn emanation equals 2ɛ. This is in agreement with the hypothesis that222Rn activity can be used as a first approximation for input by recoil (Krishnaswamiet al 1982). However, high222Rn emanation cannot be explained by production from the surface layer as formulated in the model. Other possibilities involve
models including surface precipitation, where the surface layer is not in steady-state. 相似文献
10.
Accurate measurements of soil CO2 concentrations (pCO2) are important for understanding carbonic acid reaction pathways for continental weathering and the global carbon (C) cycle. While there have been many studies of soil pCO2, most sample or model only one, or at most a few, landscape positions and therefore do not account for complex topography. Here, we test the hypothesis that soil pCO2 distribution can predictably vary with topographic position. We measured soil pCO2 at the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), Pennsylvania, where controls on soil pCO2 (e.g., depth, texture, porosity, and moisture) vary from ridge tops down to the valley floor, between planar slopes and slopes with convergent flow (i.e., swales), and between north and south-facing aspects. We quantified pCO2 generally at 0.1–0.2 m depth intervals down to bedrock from 2008 to 2010 and in 2013. Of the variables tested, topographic position along catenas was the best predictor of soil pCO2 because it controls soil depth, texture, porosity, and moisture, which govern soil CO2 diffusive fluxes. The highest pCO2 values were observed in the valley floor and swales where soils are deep (≥0.7 m) and wet, resulting in low CO2 diffusion through soil profiles. In contrast, the ridge top and planar slope soils have lower pCO2 because they are shallower (≤0.6 m) and drier, resulting in high CO2 diffusion through soil profiles. Aspect was a minor predictor of soil pCO2: the north (i.e., south-facing) swale generally had lower soil moisture content and pCO2 than its south (i.e., north-facing) counterpart. Seasonally, we observed that while the timing of peak soil pCO2 was similar across the watershed, the amplitude of the pCO2 peak was higher in the deep soils due to more variable moisture content. The high pCO2 observed in the deeper, wetter topographic positions could lower soil porewater pH by up to 1 pH unit compared to porewaters equilibrated with atmospheric CO2 alone. CO2 is generally the dominant acid driving weathering in soils: based on our observations, models of chemical weathering and CO2 dynamics would be improved by including landscape controls on soil pCO2. 相似文献
11.
《Applied Geochemistry》2001,16(7-8):745-758
The physical–chemical characteristics of the groundwater in the Baza–Caniles detrital aquifer system indicate that a wide diversity of hydrochemical conditions exists in this semiarid region, defining geochemical zones with distinct groundwater types. The least mineralized water is found closest to the main recharge zones, and the salinity of the water increases significantly with depth towards the center of the basin. Geochemical reaction models have been constructed using water chemistry data along flow paths that characterize the different sectors of the aquifer system, namely: Quaternary aquifer, unconfined sector and shallow and deep confined sectors of the Mio–Pliocene aquifer. Geochemical mass–balance calculations indicate that the dominant groundwater reaction throughout the detrital system is dedolomitisation (dolomite dissolution and calcite precipitation driven by gypsum dissolution); this process is highly developed in the central part of the basin due to the abundance of evaporites. Apart from this process, there are others which influence the geochemical zoning of the system. In the Quaternary aquifer, which behaves as a system open to gases and which receives inputs of CO2 gas derived from the intensive farming in the area, the interaction of the CO2 with the carbonate matrix of the aquifer produces an increase in the alkalinity of the water. In the shallow confined sector of the Mio–Pliocene aquifer, the process of dedolomitisation evolves in a system closed to CO2 gas. Ca2+/Na+ cation exchange and halite dissolution processes are locally important, which gives rise to a relatively saline water. Finally, in the deep confined sector, a strongly reducing environment exists, in which the presence of H2S and NH+4 in the highly mineralized groundwater can be detected. In this geochemical zone, the groundwater system is considered to be closed to CO2 gas proceeding from external sources, but open to CO2 from oxidation of organic matter. The geochemical modeling indicates that the chemical characteristics of this saline water are mainly due to SO4 dissolution, dedolomitisation and SO4 reduction, coupled with microbial degradation of lignite. 相似文献
12.
Cave air control on dripwater geochemistry, Obir Caves (Austria): Implications for speleothem deposition in dynamically ventilated caves 总被引：11，自引：0，他引：11
There are very few process studies that demonstrate the annual variation in cave environments depositing speleothems. Accordingly, we initiated a monitoring program at the Obir Caves, an Austrian dripstone cave system characterized by a seasonally changing air flow that results in a predictable pattern of high pCO2 during summer and low pCO2 in winter. Although similar seasonal changes in soil pCO2 occur, they are not directly connected with the changes in the subsurface since the dripwaters are fed from a well-mixed source showing little seasonal variation. Cold season flushing by relatively CO2-poor air enhances degassing of CO2 in the cave and leads to a high degree of supersaturation of dripwater with regard to calcite. Forced calcite deposition during the cold season also gives rise to a pronounced pattern of synchronous seasonal variations in electrical conductivity, alkalinity, pH, Ca and δ13CDIC which parallel variations recorded in δ13Ccave air. Chemical components unaffected by calcite precipitation (e.g., δD, δ18O, SiO2, SO4) lack a seasonal signal attesting to a long residence in the karst aquifer. Modeling shows that degassing of CO2 from seepage waters results in kinetically-enhanced C isotopic fractionation, which contrasts with the equilibrium degassing shown from the Soreq cave in Israel. The Obir Caves may serve as a case example of a dripstone cave whose seepage waters (and speleothems) show intra-annual geochemical variability that is primarily due to chemical modification of the groundwater by a dynamic, bidirectional subsurface air circulation. 相似文献
13.
Christopher W. Hunt Joseph E. Salisbury Douglas Vandemark 《Estuaries and Coasts》2014,37(5):1078-1091
Repeated surveys of the Kennebec estuary, a macrotidal river estuary in Maine, USA, between 2004 and 2008 found spatial and temporal variability both in sources of carbon dioxide (CO2) to the estuary and the air–sea flux of estuary CO2. On an annual basis, the surveyed area of the Kennebec estuary had an area-weighted average partial pressure of CO2 (pCO2) of 559 μatm. The area-weighted average CO2 flux to the atmosphere was 3.54 mol C m?2 year?1. Overall, the Kennebec estuary was an annual source of 7.2?×?107 mol CO2 to the atmosphere. Distinct seasonality in estuarine pCO2 was observed, with shifts in the seasonal pattern evident between lower and higher salinities. Fluxes of CO2 from the estuary were elevated following two summertime storms, and inputs of riverine CO2 outweighed internal estuarine CO2 inputs in nearly all months. River and estuarine inputs of CO2 represented 68 and 32 % of the total CO2 contributions to the estuary, respectively. This study examines the variability of CO2 in a large New England estuary, and highlights the comparatively high contribution of CO2 from riverine sources. 相似文献
14.
The mechanism of222Rn release into fracture fluids by direct alpha-recoil, lattice and grain boundary/micro-crack diffusion is discussed. Experimental measurements of222Rn release into surrounding air and water phases have been made for crystalline rock specimens with well defined surface areas. The222Rn flux from an infinite plane surface and hence the effective diffusion length of222Rn in the rock matrix has been estimated.The222Rn flux from plane crystalline rock surfaces has been used in conjunction with a simple hydrological model of the reservoir to calculate the222Rn content of the return fluids of a geothermal doublet circulation system. For given production rate and piezometric difference between the injection and production wells, the222Rn content of the return fluid is dependent upon the distribution of flow path lengths and fracture apertures in the reservoir. Matching of the calculated and experimental222Rn contents of the return fluids has been used to select appropriate parameters for the reservoir model and hence to estimate the extent of the heat-transfer surface. The model estimates the fracture width of the flow paths, total swept surface area and fracture volume within the reservoir. 相似文献
15.
Marco Tallini Barbara Parisse Marco Petitta Michele Spizzico 《Hydrogeology Journal》2013,21(7):1447-1467
In the Gran Sasso fissured carbonate aquifer (central Italy), a long-term (2001–2007) spatio-temporal hydrochemical and 222Rn tracing survey was performed with the goal to investigate groundwater flow and water–rock interaction. Analyses of the physico-chemical parameters, and comparisons of multichemical and characteristic ratios in space and time, and subsequent statistical analyses, permitted a characterisation of the hydrogeology. At the regional scale, groundwater flows from recharge areas to the springs located at the aquifer boundaries, with a gradual increase of mineralisation and temperature along its flowpaths. However, the parameters of each group of springs may significantly deviate from the regional trend owing to fast flows and to the geological setting of the discharge spring areas, as corroborated by statistical data. Along regional flowpaths, the effects of seasonal recharge and lowering of the water table clearly cause changes in ion concentrations over time. This conceptual model was validated by an analysis of the 222Rn content in groundwater. 222Rn content, for which temporal variability depends on seasonal fluctuations of the water table, local lithology and the fracture network at the spring discharge areas, was considered as a tracer of the final stages of groundwater flowpaths. 相似文献
16.
This contribution analyzes the similarities and differences between the measured activities of 137Cs and excess 210pb （210Pbex） in the cultivated brown and cinnamon soils of the Yimeng Mountain area, discusses the influ- ence of soil texture on the measurement of 210Pbex, and presents differences between the two types of soils. Fields A and B were selected to represent the fields that contain cultivated brown and cinnamon soils, respectively. From either study field, one site of sectioned core and six bulk cores were collected to measure 137Cs levels, 210Pbex levels, and the particle-size composition of soil samples. Three undisturbed soil samples were collected to measure capillary and aeration porosities. The 137Cs inventories for the two study fields are very similar. The 137Cs is a man-made ra- dionuclide, which means that its measured levels for soils are unaffected by soil texture. In contrast, levels of the naturally occurring 210Pbex of soils from Field A were lower than those of Field B by about 50%. In contrast to aquatic sediments, levels of 210Pbex in terrestrial surface soils are affected by the emanation of 222Rn from the soils. It can be assumed that the coarser the soils, the greater the emanation of 222Rn; in addition, the lower the measured 210pbex, the greater the underestimate of this value. The cultivated brown soils in Field A are coarser than the culti- vated cinnamon soils in Field B. As a result, 222Rn in Field A will diffuse more easily into the atmosphere than that in Field B. As a consequence, the measured 210pbex in soils from Field A is much lower than the actual value, whereas the value measured for Field B is much closer to the actual value. 相似文献
17.
Ryoko Fujiyoshi Masanori Okabayashi Yousuke Sakuta Kazumasa Okamoto Takashi Sumiyoshi Ivan Kobal Janja Vaupotič 《Environmental Earth Sciences》2013,70(3):1159-1167
Soil radon (222Rn) has been monitored during winter months under cool-temperate deciduous stands of different surface geology in Tomakomai and in Sapporo, Hokkaido, Japan. Radon level was lower in Tomakomai of immature soil of porous volcanic ash emitted from an active volcano (Mt. Tarumae), compared with those in Sapporo of alluvial sediments. In Tomakomai, mean value of the 222Rn activity concentration was higher in winter (570 Bq m?3) than in summer (350 Bq m?3) at a depth of 1 m, which is consistent with the results in cold and dry winter reported in the literature. In contrast, soil radon decreasing with decreasing soil temperature from mid-September (5.0 kBq m?3) remained low (2.6 kBq m?3) under persistent snow in Sapporo, which had already been observed in the same location. Measurements of the activity concentrations of 222Rn in snow and in snow air as well as in soil air indicate that the small amount of 222Rn is released from the ground surface to the overlying snowpack with a 222Rn flux density of 0.4 mBq m?2 s?1 under thick snow cover in Sapporo. 相似文献
18.
Controls governing the production of 4He and 222Rn in the solid phase as well as parameters and processes contributing to their transport into the pore fluid are discussed. 222Rn activity is used to quantify the uranium sources for 4He and the result is a simplified pore-fluid age equation which is virtually independent of the porosity, the water/rock ratio, the rock density and the uranium concentration, but does require a Th/U estimate. The crucial parameter is the ratio of the release factors for the two species, /GLRn//GLHe, which is discussed in terms of three possible release mechanisms: (1) recoil; (2) recoil followed by diffusion; and (3) weathering release of accumulated 4He. It was found that /GLRn//GLHe can vary over several orders of magnitude, but can be expressed in terms of the effective grain size r, and the diffusive half-length for 222Rn decay, re.4He measurements are used to “date” gases from known gas fields and the agreement with the assumed source-rock age is good. Application of 4He/ 222Rn measurements to continental freshwater springs indicates that the weathering release of accumulated 4He dominates the input and results in a large overestimate of groundwater age. Measurement in the Lardarello geothermal field indicates that the 4He/222Rn method can indicate relative transport direction. Other possible applications in various geochemical fields are suggested. 相似文献
19.
The study reports the age evolution of groundwater as it flows from the recharge area through a regional alluvial aquifer system in North Gujarat-Cambay region in western India. Radiocarbon (14C), 4He and 4He / 222Rn dating methods have been employed. Sediments from a drill core in the Cambay Basin were also analysed for uranium (U) and thorium (Th) concentrations and the measured values have been used to estimate the 4He and 222Rn production rate for groundwater age calculations. Additionally, factors controlling the distribution of 222Rn, 4He and temperature anomalies in groundwater, vis-à-vis their relation to the tectonic framework and lithology of the study area, have also been examined.The multi-isotope study indicated a reasonable correspondence in groundwater age estimates by the three methods employed. The groundwater 14C ages increased, progressively, in the groundwater flow direction: from the foothills of Aravalli Mountains in the east, and reached a value of ∼35 ka towards the region of lowest elevation, linking Little Rann of Kachchh (LRK)-Nalsarovar (NS)-Gulf of Khambhat (GK) in the western part of the study area. In this region, groundwater ages obtained for free flowing thermal wells and springs employing 4He and 4He / 222Rn systematics are in the order of million years. Such anomalous ages are possibly due to enhanced mobilisation and migration of ‘excess helium’ from hydrothermal circulation vents along deep-seated faults. Excluding such anomalous cases and considering all uncertainties, presently estimated 4He and 4He / 222Rn groundwater ages are in reasonable agreement with 14C age estimates in the Cambay Basin for helium release factor (ΛHe) value of 0.4 ± 0.3. The 4He method also indicated west-southwards progression of groundwater ages up to ∼100 ka beyond the Cambay Basin.Large ‘excess helium’ concentrations are also seen to be generally associated with anomalous groundwater temperatures (> 35 °C) and found to overlie some of the basement faults in the study area, particularly along the east and the west flanks of the Cambay Basin. Groundwater 222Rn activities in most of the study area are 800 ± 400 dpm/l. But, a thermal spring at Tuwa on the east flank of the Cambay Basin, having granitic basement at shallow depth, recorded the highest 222Rn activity (∼63,000 dpm/l). 相似文献
20.
Geochemical detection of carbon dioxide in dilute aquifers 总被引：1，自引：0，他引：1