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1.
Jin, Z. D., Bickle, M. J., Chapman, H. J., Yu, J., An, Z., Wang, S. & Greaves, M. J. 2010: Ostracod Mg/Sr/Ca and 87Sr/86Sr geochemistry from Tibetan lake sediments: Implications for early to mid‐Pleistocene Indian monsoon and catchment weathering. Boreas, 10.1111/j.1502‐3885.2010.00184.x. ISSN 0300‐9483 Lacustrine sediment serves as a valuable archive for tracing catchment weathering processes associated with past climatic and/or tectonic changes. High‐resolution records of fossil ostracod Mg/Ca, Sr/Ca and 87Sr/86Sr ratios from a lake sediment core from the central Tibetan Plateau reveal a temporal link between lake‐water chemistry and catchment weathering and distinct monsoonal oscillations over the early to mid‐Pleistocene. Between 2.01 and 0.95 Ma, lake‐water chemistry was dominated by a high proportion of carbonate weathering related to variations in the Indian monsoon, resulting in relatively low and constant ostracod 87Sr/86Sr but obvious fluctuations in Mg/Ca, Sr/Ca and δ18O. Across the mid‐Pleistocene transition (MPT), a significant increase in 87Sr/86Sr and frequently fluctuating ratios of ostracod Mg/Ca, Sr/Ca and δ18O are coincident with increases in both Chinese loess grain size and Arabian Sea lithogenic flux. This correlation indicates an increased glaciation and a strong monsoon seasonal contrast over the plateau. The increase in lake‐water 87Sr/86Sr across the MPT highlights a change in catchment weathering patterns, rather than one in climate‐enhanced weathering intensity, with an increased weathering of 87Sr‐rich minerals potentially induced by marked extensive glaciation and strong seasonality in the central plateau.  相似文献   

2.
The Nandong Underground River System (NURS) is located in a typical karst area dominated by agriculture in SE Yunnan Province, China. Groundwater plays an important role in the social and economical development in the area. The effects of human activities (agriculture and sewage effluents) on the Sr isotope geochemistry were investigated in the NURS. Seventy-two representative groundwater samples, which were collected from different aquifers (calcite and dolomite), under varying land-use types, both in summer and winter, showed significant spatial differences and slight seasonal variations in Sr concentrations and 87Sr/86Sr ratios. Agricultural fertilizers and sewage effluents significantly modified the natural 87Sr/86Sr ratios signature of groundwater that was otherwise dominated by water-rock interaction. Three major sources of Sr could be distinguished by 87Sr/86Sr ratios and Sr concentrations in karst groundwater. Two sources of Sr are the Triassic calcite and dolomite aquifers, where waters have low Sr concentrations (0.1-0.2 mg/L) and low 87Sr/86Sr ratios (0.7075-0.7080 and 0.7080-0.7100, respectively); the third source is anthropogenic Sr from agricultural fertilizers and sewage effluents with waters affected having radiogenic 87Sr/86Sr ratios (0.7080-0.8352 for agricultural fertilizers and 0.7080-0.7200 for sewage effluents, respectively), with higher Sr concentrations (0.24-0.51 mg/L). Due to the overlapping 87Sr/86Sr ratios, it is difficult to distinguish the sources of Sr in groundwater samples contaminated by agricultural fertilizers or sewage effluents based only on their 87Sr/86Sr ratios. However, 87Sr/86Sr ratios do provide key information for natural and anthropogenic sources in karst groundwater.  相似文献   

3.
《Applied Geochemistry》2002,17(3):285-300
Strontium and particularly 87Sr/86Sr ratios in stream water have often been used to calculate weathering rates in catchments. Nevertheless, in the literature, discharge variation effects on the geochemical behavior of Sr are often omitted or considered as negligible. A regular survey of both Sr concentrations and Sr isotope ratios of the Strengbach stream water draining a granite (Vosges mountains, France) has been performed during one year. The results indicate that during low water flow periods, waters contain lower Sr concentrations and less radiogenic Sr isotope ratios (Sr=11.6 ppb and 87Sr/86Sr=0.7246 as an average, respectively) than during high water flow periods (Sr= 13 ppb and 87Sr/86Sr=0.7252 as an average, respectively). This is contrary to expected dilution processes by meteoric waters which have comparatively lower Sr isotopic ratios and lower Sr concentrations. Furthermore, 87Sr/86Sr ratios in stream water behave in 3 different ways depending on moisture and on hydrological conditions prevailing in the catchment. During low water flow periods (discharge < 9 l/s), a positive linear relationship exists between Sr isotope ratio and discharge, indicating the influence of radiogenic waters draining the saturated area during storm events. During high water flow conditions, rising discharges are characterized by significantly less radiogenic waters than the recession stages of discharge. This suggests a large contribution of radiogenic waters draining the deep layers of the hillslopes during the recession stages, particularly those from the more radiogenic north-facing slopes. These results allow one to confirm the negligible instantaneous incidence of rainwater on stream water chemistry during flood events, as well as the existence in the catchment of distinct contributive areas and reservoirs. The influence of these areas or reservoirs on the fluctuations of Sr concentrations and on Sr isotopic variations in stream water depends on both moisture and hydrological conditions. Hence, on a same bedrock type, 87Sr/86Sr ratios in surface waters can be related to flow rate. Consequently, discharge variations must be considered as a pre-requisite when using Sr isotopes for calculating weathering rates in catchments, particularly to define the range of variations of the end-members.  相似文献   

4.
Exhumation of the Himalayan-Tibetan orogen is implicated in the marked rise in seawater 87Sr/86Sr ratios since 40 Ma. However both silicate and carbonate rocks in the Himalaya have elevated 87Sr/86Sr ratios and there is disagreement as to how much of the 87Sr flux is derived from silicate weathering. Most previous studies have used element ratios from bedrock to constrain the proportions of silicate- and carbonate-derived Sr in river waters. Here we use arrays of water compositions sampled from the head waters of the Ganges in the Indian and Nepalese Himalaya to constrain the end-member element ratios. The compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two-component mixing of silicate and carbonate-derived components and lie on a plane in multicomponent composition space. Key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes Na = 0 for carbonate and constant Ca/Na for silicate. The fractions of Sr derived from silicate and carbonate sources are then calculated by mass-balance in Sr-Ca-Mg-Na composition space. Comparison of end-member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low-Mg trace calcite in silicate rocks may explain discrepancies in Sr-Ca-Na-Mg covariation. Alternatively, composition-dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation-ratio diagrams. However the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained. Silicates are calculated to provide ∼50% of the dissolved Sr flux from the head waters of the Ganges assuming that discrepancies between Ca-Mg-Na covariation and the silicate rock compositions arise from addition of trace calcite. If the Ca-Mg-Na mixing plane is rotated by composition-dependent secondary calcite deposition, this estimate would be increased. Moreover, when 87Sr/86Sr ratios of the Sr inputs are considered, silicate Sr is responsible for 70 ± 16% (1σ) of the 87Sr flux forcing changes in seawater Sr-isotopic composition. Since earlier studies predict that silicate weathering generates as little as 20% of the total Sr flux in Himalayan river systems, this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated.  相似文献   

5.
《Chemical Geology》2007,236(3-4):281-290
Ostracods preserved in late Quaternary sediments of Wallywash Great Pond, a fresh coastal lake in SW Jamaica, record temporal variations in the strontium-isotope composition of lake water. Oxygen-isotope and Sr/Ca ratios in ostracods reveal temporal variations in the lake's hydrology, related to effective precipitation, and in its salinity related to varying marine-saline groundwater input from changes in relative sea level. Evaluation of isotopic and trace-element data indicates that the stratigraphic variations in 87Sr/86Sr ratios during the late Quaternary are best explained by climatically-controlled hydrological changes. During wetter periods, the lake's Sr budget was dominated by springwater input with relatively low 87Sr/86Sr ratio, whereas during drier times reduced springflow, possibly coupled with input of more-radiogenic Sr from other sources, such as sea-spray aerosols and perhaps Saharan dust, led to an increase in the Sr-isotope ratio of the lake water. Despite proximity of the lake to the sea and evidence for slight intrusion of marine saline groundwater in the past, however, the extent of marine input appears to have had limited influence on the lake's Sr-isotope ratios. Whereas the 87Sr/86Sr ratios cannot be used as a palaeosalinity proxy in this particular lake, they do provide valuable information about the mechanisms underlying hydrological change.  相似文献   

6.
《Applied Geochemistry》2000,15(3):311-325
Barium/Sr and Ca/Sr ratios have been used to model the relative importance of different sources of stream water. Major and trace element concentrations together with 87Sr/86Sr ratios were measured in precipitation, soil water, groundwater and stream water in a small (9.4 km2) catchment in northern Sweden. The study catchment is drained by a first order stream and mainly covered with podzolized Quaternary till of granitic composition. It is underlain by a 1.8 Ga granite. A model with mixing equations used in an iterative mode was developed in order to separate the stream water into 3 subsurface components: soil water, shallow groundwater, and deep groundwater. Contributions from precipitation are thus not included in the model. This source may be significant for the stream water generation, but it does not interfere with the calculations of the relative contributions from the subsurface components. The results show that the deep groundwater constitutes between 5 and 20% of the subsurface water discharge into the stream water. The highest values of the deep groundwater fraction occur during base flow. Soil water dominates during snowmelt seasons, whereas during base flow it is the least important fraction. Soil water accounts for 10–100% of the subsurface water discharge into the stream water. Shallow groundwater accounts for up to 80% of the subsurface water discharge with the lowest values at peak discharge during snowmelt seasons and the highest values during base flow. The validity of the model was tested by comparing the measured 87Sr/86Sr ratios in the stream water with the 87Sr/86Sr ratios predicted by the model. There was a systematic difference between the measured and modelled 87Sr/86Sr ratios which suggests that the fraction of soil water is overestimated by the model, especially during spring flood. As a consequence of this overestimation of soil water the amount of shallow groundwater is probably underestimated during this period. However, it is concluded that the differences between measured and predicted values are relatively small, and that element ratios are potentially effective tracers for different subsurface water flowpaths in catchments.  相似文献   

7.
We have collected and analyzed a series of water samples from three closed-basin lakes (Lakes Bonney, Fryxell, and Hoare) in Taylor Valley, Antarctica, and the streams that flow into them. In all three lakes, the hypolimnetic waters have different 87Sr/86Sr ratios than the surface waters, with the deep water of Lakes Fryxell and Hoare being less radiogenic than the surface waters. The opposite occurs in Lake Bonney. The Lake Fryxell isotopic ratios are lower than modern-day ocean water and most of the whole-rock ratios of the surrounding geologic materials. A conceivable source of Sr to the system could be either the Cenozoic volcanic rocks that make up a small portion of the till deposited in the valley during the Last Glacial Maximum or from marble derived from the local basement rocks. The more radiogenic ratios from Lake Bonney originate from ancient salt deposits that flow into the lake from Taylor Glacier and the weathering of minerals with more radiogenic Sr isotopic ratios within the tills. The Sr isotopic data from the streams and lakes of Taylor Valley strongly support the notion documented by previous investigators that chemical weathering has been, and is currently, a major process in determining the overall aquatic chemistry of these lakes in this polar desert environment.  相似文献   

8.
Geochemical methods (major elements and Sr, Nd isotopes) have been used to (1) characterize Lake Le Bourget sediments in the French Alps, (2) identify the current sources of the clastic sediments and estimate the source variability over the last 600 years. Major element results indicate that Lake Le Bourget sediments consist of 45% clastic component and 55% endogenic calcite. In addition, several individual flood levels have been identified during the Little Ice Age (LIA) on the basis of their higher clastic content (> 70%).Potential sources of Lake Le Bourget clastic sediments have been investigated from Sr and Nd isotope compositions. The sediments from the Sierroz River and Leysse River which are mainly derived from the Mesozoic Calcareous Massifs are characterised by lower 87Sr/86Sr ratios and slightly lower ?Nd(0) ratios than the Arve River sediments which are derived from the Palaeozoic Mont-Blanc External Crystalline Massifs. The Rhône River appears to have been the main source of clastic sediments into the lake for the last 600 years, as evidenced by a similar Sr and Nd isotopic compositions analyzed in core B16 sediments (87Sr/86Sr = 0.719, ?Nd(0) = − 10) and in the sediments of the Rhône River (87Sr/86Sr = 0.719, ?Nd(0) = − 9.6).The isotopic signatures of flood events and background samples from core B16 in Lake Le Bourget are also similar. This indicates that prior to ∼ 1800, the inputs into the lake have remained relatively homogeneous with the proportion of clastic component mainly being a function of the palaeohydrology of the Rhone River. Early human modification (deforestation and agriculture) of the lake catchment before the 1800s appears to have had little influence on the source of clastic sediments.  相似文献   

9.
Magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the Moselle basin, northeastern France. This small basin is remarkable for its well-constrained and varied lithology on a small distance scale, and this is reflected in river water Sr isotope compositions. Upstream, where the Moselle River drains silicate rocks of the Vosges mountains, waters are characterized by relatively high 87Sr/86Sr ratios (0.7128-0.7174). In contrast, downstream of the city of Epinal where the Moselle River flows through carbonates and evaporites of the Lorraine plateau, 87Sr/86Sr ratios are lower, down to 0.70824.Magnesium in river waters draining silicates is systematically depleted in heavy isotopes (δ26Mg values range from −1.2 to −0.7‰) relative to the value presently estimated for the continental crust and a local diorite (−0.5‰). In comparison, δ26Mg values measured in soil samples are higher (∼0.0‰). This suggests that Mg isotope fractionation occurs during mineral leaching and/or formation of secondary clay minerals. On the Lorraine plateau, tributaries draining marls, carbonates and evaporites are characterized by low Ca/Mg (1.5-3.2) and low Ca/Sr (80-400) when compared to local carbonate rocks (Ca/Mg = 29-59; Ca/Sr = 370-2200), similar to other rivers draining carbonates. The most likely cause of the Mg and Sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer. δ26Mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year (from −1.4‰ to −1.6‰ and from −1.2‰ to −1.4‰, respectively), within the range defined for the underlying rocks. Downstream of Epinal, the compositions of the Moselle River samples in a δ26Mg vs. 87Sr/86Sr diagram can be explained by mixing curves between silicate, carbonate and evaporite waters, with a significant contribution from the Vosgian silicate lithologies (>70%). Temporal co-variation between δ26Mg and 87Sr/86Sr for the Moselle River throughout year is also observed, and is consistent with a higher contribution from the Vosges mountains in winter, in terms of runoff and dissolved element flux. Overall, this study shows that Mg isotopes measured in waters, rocks and soils, coupled with other tracers such as Sr isotopes, could be used to better constrain riverine Mg sources, particularly if analytical uncertainties in Mg isotope measurements can be improved in order to perform more precise quantifications.  相似文献   

10.
《Applied Geochemistry》1998,13(4):463-475
Strontium isotope ratios were measured on 13 rock, 18 leachate and 28 pore-water samples from the Milk River aquifer, the confining argillaceous formations, and the glacial till mantling the recharge area. Strontium isotope ratios (87Sr/86Sr) of pore waters from the aquifer, confining units, and the glacial till ranged from 0.7069 to 0.7082. The 87Sr/86Sr ratios in aquifer pore waters decrease with increasing distance from the aquifer recharge area, and this is interpreted to be the result of mixing and water–rock interaction within the aquifer.The solute composition of the recharging groundwater is modified by the local lithology, causing distinct geochemical patterns along different flow paths within the aquifer. Whole-rock 87Sr/86Sr ratios indicate that the shales and till are generally more radiogenic than the aquifer sandstone. The authigenic carbonate cements and rock-forming minerals comprising the major lithologic units had little apparent influence on the pore-water Sr chemistry. Carbonate cement leachates from the till and the aquifer sandstone are more radiogenic than those from the confining shale formations. Feldspar separates from the aquifer sandstone have relatively radiogenic Sr isotope ratios, whereas bentonites from the Milk River and Colorado Shale Formations have whole-rock and leachate Sr isotope ratios that are relatively unradiogenic. Ratios of most Milk River aquifer pore waters are lower than those of any leachates or whole rocks analyzed, except the bentonites.The 87Sr/86Sr ratios of exchangeable Sr in the bentonites are similar to ratios found in the more evolved pore waters. Simple rock–water interaction models calculated for the whole-rock, leachate, and exchangeable-ion/pore-water pairs indicate that ion exchange with bentonite clays within the Milk River and Colorado Shale Formations appears to influence the isotopic evolution of the pore-water Sr in each of these units.  相似文献   

11.
Analyses of environmental isotopes (18O, 2H, and 87Sr/86Sr) are applied to groundwater studies with emphasis on saline groundwater in aquifers in the Keta Basin, Ghana. The 87Sr/86Sr ratios of groundwater and surface water of the Keta Basin primarily reflect the geology and the mineralogical composition of the formations in the catchments and recharge areas. The isotopic compositions of 18O and 2H of deep groundwater have small variations and plot close to the global meteoric water line. Shallow groundwater and surface water have considerably larger variations in isotopic compositions, which reflect evaporation and preservation of seasonal fluctuations. A significant excess of chloride in shallow groundwater in comparison to the calculated evaporation loss is the result of a combination of evaporation and marine sources. Groundwaters from deep wells and dug wells in near-coastal aquifers are characterized by relatively high chloride contents, and the significance of marine influence is evidenced by well-defined mixing lines for strontium isotopes, and hydrogen and oxygen stable isotopes, with isotopic compositions of seawater as one end member. The results derived from environmental isotopes in this study demonstrate that a multi-isotope approach is a useful tool to identify the origin and sources of saline groundwater. Electronic Publication  相似文献   

12.
In this study, the chemical and Sr isotopic compositions of shallow groundwater and rainwater in the Ordos Desert Plateau, North China, and river water from the nearby Yellow River, are investigated to determine the dissolved Sr source and water–rock interactions, and quantify the relative Sr contribution from each end-member. Three groundwater systems have been identified, namely, GWS-1, GWS-2 and GWS-3 according to the watershed distribution in the Ordos Desert Plateau. Ca2+ and Mg2+ are the most dominant cations in GWS-1, while Na+ is dominant in GWS-3. In addition, there is more SO42− and less Cl− in GWS-1 than in GWS-3. The shallow groundwater in GWS-2 seems to be geochemically between that in GWS-1 and GWS-3. The 87Sr/86Sr ratios of the shallow groundwater are high in GWS-1 and GWS-2 and are low in GWS-3. By geochemically comparing the nearby Yellow River, local precipitation and deep groundwater, the shallow groundwater is recharged only by local precipitation. The ionic and isotopic ratios indicate that carbonate dissolution is an important process controlling the chemistry of the shallow groundwater. The intensity of the water–rock interactions varies among the three groundwater systems and even within each groundwater system. Three end-members controlling the groundwater chemistry are isotopically identified: (1) precipitation infiltration, (2) carbonate dissolution and (3) silicate weathering. The relative Sr contributions of the three end-members show that precipitation infiltration and carbonate dissolution are the primary sources of the shallow groundwater Sr in GWS-3 whereas only carbonate dissolution is responsible for the shallow groundwater Sr in GWS-1 and GWS-2. Silicate weathering seems insignificant towards the shallow groundwater's chemistry in the Ordos Desert Plateau. This study is helpful for understanding groundwater chemistry and managing water resources.  相似文献   

13.
A 4-yr study of spatial and temporal variability in the geochemistry of vadose groundwaters from caves within the Edwards aquifer region of central Texas offers new insights into controls on vadose groundwater evolution, the relationship between vadose and phreatic groundwaters, and the fundamental influence of soil composition on groundwater geochemistry. Variations in Sr isotopes and trace elements (Mg/Ca and Sr/Ca ratios) of dripwaters and soils from different caves, as well as phreatic groundwaters, provide the potential to distinguish between local variability and regional processes controlling fluid geochemistry, and a framework for understanding the links between climatic and hydrologic processes.The Sr isotope compositions of vadose cave dripwaters (mean 87Sr/86Sr = 0.7087) and phreatic groundwaters (mean 87Sr/86Sr = 0.7079) generally fall between values for host carbonates (mean 87Sr/86Sr = 0.7076) and exchangeable Sr in overlying soils (mean 87Sr/86Sr = 0.7088). Dripwaters have lower Mg/Ca and Sr/Ca ratios, and higher 87Sr/86Sr values than phreatic groundwaters. Dripwater 87Sr/86Sr values also inversely correlate with both Mg/Ca and Sr/Ca ratios. Mass-balance modeling combined with these geochemical relationships suggest that variations in fluid compositions are predominantly controlled by groundwater residence times, and water-rock interaction with overlying soils and host aquifer carbonate rocks. Consistent differences in dripwater geochemistry (i.e., 87Sr/86Sr, Mg/Ca, and Sr/Ca) between individual caves are similar to compositional differences in soils above the caves. While these differences appear to exert significant control on local fluid evolution, geochemical and isotopic variations suggest that the controlling processes are regionally extensive. Temporal variations in 87Sr/86Sr values and Mg/Ca ratios of dripwaters from some sites over the 4-yr interval correspond with changes in both aquifer and climatic parameters. These results have important implications for the interpretation of trace element and isotopic variations in speleothems as paleoclimate records, as well as the understanding of controls on water chemistry for both present-day and ancient carbonate aquifers.  相似文献   

14.
We have developed an 87Sr/86Sr, 234U/238U, and δ18O data set from carbonates associated with late Quaternary paleolake cycles on the southern Bolivian Altiplano as a tool for tracking and understanding the causes of lake-level fluctuations. Distinctive groupings of 87Sr/86Sr ratios are observed. Ratios are highest for the Ouki lake cycle (120-95 ka) at 0.70932, lowest for Coipasa lake cycle (12.8-11.4 ka) at 0.70853, and intermediate at 0.70881 to 0.70884 for the Salinas (95-80 ka), Inca Huasi (~ 45 ka), Sajsi (24-20.5 ka), and Tauca (18.1-14.1 ka) lake cycles. These Sr ratios reflect variable contributions from the eastern and western Cordilleras. The Laca hydrologic divide exerts a primary influence on modern and paleolake 87Sr/86Sr ratios; waters show higher 87Sr/86Sr ratios north of this divide. Most lake cycles were sustained by slightly more rainfall north of this divide but with minimal input from Lake Titicaca. The Coipasa lake cycle appears to have been sustained mainly by rainfall south of this divide. In contrast, the Ouki lake cycle was an expansive lake, deepest in the northern (Poópo) basin, and spilling southward. These results indicate that regional variability in central Andean wet events can be reconstructed using geochemical patterns from this lake system.  相似文献   

15.
《Applied Geochemistry》2005,20(4):749-766
A synthesis of Sr isotope data from shallow and deep groundwaters, and brines from the Fennoscandian and Canadian Shields is presented. A salinity gradient is evident in the water with concentrations varying from approximately 1–75 g L−1 below 1500 m depth in the Fennoscandian Shield and from 10 up to 300 g L−1 below 650 m depth in the Canadian Shield. Strontium isotope ratios were measured to assess the origin of the salinity and evaluate the degree of water–rock interaction in the systems. In both shields, the Sr concentrations are enriched relative to Cl, defining a positive trend parallel to the seawater dilution line and indicative of Sr addition through weathering processes. The depth distribution for Sr concentration increases strongly with increasing depth in both shields although the variation in Sr-isotope composition does not mirror that of Sr concentrations. Strontium-isotope compositions are presented for surface waters, and groundwaters in several sites in the Fennoscandian and Canadian Shields. Numerous mixing lines can be drawn reflecting water–rock interaction. A series of calculated lines links the surface end-members (surface water and shallow groundwater) and the deep brines; these mixing lines define a range of 87Sr/86Sr ratios for the deep brines in different selected sites. All sites show a specific 87Sr/86Sr signature and the occurrence of large 87Sr/86Sr variations is site specific in both shields. In Canadian Shield brines, the Sr isotope ratios clearly highlight large water rock interaction that increases the 87Sr/86Sr ratio from water that could have been of marine origin. In contrast to the Canadian Shield, groundwater does not occur in closed pockets in the Fennoscandian, and the well-constrained 87Sr/86Sr signatures in deep brines should correspond to a large, well-mixed and homogeneous water reservoir, whose Sr isotope signature results from water–rock interaction.  相似文献   

16.
Rare earth element (REE) and strontium isotope data (87Sr/86Sr) are presented for hydromagnesite and surface waters that were collected from Dujiali Lake in central Qinghai-Tibet Plateau (QTP), China. The goal of this study is to constrain the solute sources of hydromagnesite deposits in Dujiali Lake. All lake waters from the area exhibit a slight LREE enrichment (average [La/Sm]PAAS = 1.36), clear Eu anomalies (average [Eu/Eu*]PAAS = 1.31), and nearly no Ce anomalies. The recharge waters show a flat pattern (average [La/Sm]PAAS = 1.007), clear Eu anomalies (average [Eu/Eu*] PAAS = 1.83), and nearly no Ce anomalies (average [Ce/Ce*]PAAS = 1.016). The REE+Y data of the surface waters indicate the dissolution of ultramafic rock at depth and change in the hydrogeochemical characteristics through fluid-rock interaction. These data also indicate a significant contribution of paleo-groundwater to the formation of hydromagnesite, which most likely acquired REE and Sr signatures from the interaction with ultramafic rocks. The 87Sr/86Sr data provide additional insight into the geochemical evolution of waters of the Dujiali Lake indicating that the source of Sr in the hydromagnesite does not directly derive from surface water and may have been influenced by both Mg-rich hydrothermal fluids and meteoric water. Additionally, speciation modeling predicts that carbonate complexes are the most abundant dissolved REE species in surface water. This study provides new insights into the origins of hydromagnesite deposits in Dujiali Lake, and contributes to the understanding of hydromagnesite formation in similar modern and ancient environments on Earth.  相似文献   

17.
《Applied Geochemistry》2000,15(4):493-500
A study was undertaken to explore whether the isotopic compositions of Pb and Sr are useful to distinguish mixtures of uncontaminated groundwater, seawater, and landfill leachate at the Fresh Kills landfill, Staten Island, New York. Ratios of 87Sr/86Sr ranged from 0.7088 to 0.7137 and could be used to distinguish Sr that was derived from seawater from that in uncontaminated groundwater. Lead isotopic abundances did not vary systematically among the different water sources. Plots of 87Sr/86Sr versus dissolved organic C, B, and NH4+ defined perpendicular trends, documenting where leachate or sea water mixed with uncontaminated groundwater, and demonstrating that leachate has not contaminated groundwater in aquifers beneath the landfill.  相似文献   

18.
《Applied Geochemistry》2003,18(1):117-125
This paper describes the results of a study that was conducted to determine the relationship between hydrogeochemical composition and 87Sr/86Sr isotope ratios of the Mt. Vulture spring waters. Forty samples of spring waters were collected from local outcrops of Quaternary volcanites. Physico-chemical parameters were measured in the field and analyses completed for major and minor elements and 87Sr/86Sr isotopic ratios. A range of water types was distinguished varying from alkaline-earth bicarbonate waters, reflecting less intense water–rock interaction processes to alkali bicarbonate waters, probably representing interaction with volcanic rocks of Mt. Vulture and marine evaporites. The average 87Sr/86Sr isotope ratios suggest at least 3 different sources. However, some samples have average Sr isotope ratios (0.70704–0.70778) well above those of the volcanites. These ratios imply interaction with other rocks having higher 87Sr/86Sr ratios, probably Triassic evaporites, which is substantiated by their higher content of Na, SO4 and Cl. The Sr isotope ratios for some samples (e.g. Toka and Traficante) are intermediate between the value for the Vulture volcanites and that for the local Mesozoic rocks. The salt content of these samples also lies between the value for waters interacting solely with the volcanites and the value measured in the more saline samples. These waters are thus assumed to result from the mixing of waters circulating in volcanic rocks with waters presumably interacting with the sedimentary bedrock (marine evaporites).  相似文献   

19.
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20.
The water level of the Caspian Sea fluctuated significantly during recent history, without consensus for the cause. The varied chemistry of the Caspian, Kara Bogaz and sediment a interstitial waters provides a further insight. Element concentrations and 87Sr/86Sr ratios of the interstitial waters were compared to those of Caspian and Kara Bogaz open waters, and of acid-leached extractable components. The 87Sr/86Sr ratios of the interstitial waters are explained by addition of subterranean waters similar to nearby spring waters. These subterranean waters yield chemical characteristics such as a Cl/SO4, 87Sr/86Sr, Ca/Sr and K/Rb ratios of respectively 80, 0.7086, 250 and 1,800. However, their addition does not explain the large difference in the K/Rb ratio of the Caspian and Kara Bogaz waters, respectively at 7,630 and 17,550, which implies also a leaching of salt deposits by the upward migrating subterranean waters. The sediments of the southern Caspian basin, with low Na, Cl and SO4 in their interstitial waters, deposited apparently in an anoxic environment. The related chemical changes in the waters are also indicative of a recent change in the hydrologic regime, possibly induced by a changing morphology of the drainage basin.  相似文献   

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