Stable isotopic compositions of carbonates from the Mesoproterozoic Bangemall Group, northwestern Australia

Marine carbonate rocks from the Mesoproterozoic Bangemall Group of northwestern Australia show little deviation (+/-1.3%) in whole-rock delta 13C(carb)-values about a mean of -0.5%. This narrow range persists despite close sampling (every 10-20 m) through long sections (up to 2500 m) that are geographically widespread (up to 250 km apart), over many depositional environments (supralittoral to outer shelf), sediment sources (stromatolitic bioherms to detrital calcilutites) and rock types (pure limestones to dolomitic shales). The only major excursions from the norm seem related to unusual environmental or post-depositional processes, as they are correlated with large enrichments (to -3%) or depletions (to -16%) in 18O. Relatively heavy delta 13C-values, up to +2.5%, occur in a single bed of brecciated ferruginous dolostone at a single locality; these abnormal values may result from local evaporitic conditions. Limey and shaley nodular dolostones have delta 13C-values as low as -4.3%, probably caused by remineralization of organic matter during late and patchy dolomitization. Most notably, sharp negative excursions in delta 13C, up to -8.4%, occur in bleached kerogen-free rocks with mineral assemblages of dolomite + quartz + calcite +/- tremolite + talc, reflecting isotopic re-equilibration in thick metamorphic aureoles around dolerite intrusions. General environmental variations are minor, with delta 13C-values of peritidal facies tending to be slightly positive whereas those of subtidal facies are slightly negative. There are no strong secular trends, but subtle fluctuations within the range -2 to +l% can be correlated along the northwestern margin of the basin. This resembles the pattern seen in other Mesoproterozoic successions, but is markedly unlike the heavy background (> +5%) and extreme variations (up to l0%) in delta 13C evident in Neoproterozoic successions of similar thickness and environmental setting. Hence, in contrast to the Neoproterozoic, the global rate of organic carbon burial was probably fairly constant during deposition of the Bangemall Group, and perhaps generally during the Mesoproterozoic, as was the redox state of the atmosphere and hydrosphere.     

Stable calcium isotopic compositions of Hawaiian shield lavas: Evidence for recycling of ancient marine carbonates into the mantle

We report high-precision ⁴⁴Ca/⁴⁰Ca measurements (2σ_m < 0.06‰) of Hawaiian shield stage tholeiites. Our data reveal ∼0.3‰ variation in their ⁴⁴Ca/⁴⁰Ca, which comprises ∼20% of the ⁴⁴Ca/⁴⁰Ca variation observed in global carbonates. The ⁴⁴Ca/⁴⁰Ca variation is correlated with Sr/Nb and ⁸⁷Sr/⁸⁶Sr, and this pattern is best explained by adding up to 4% ancient carbonate into the Hawaiian plume. Mass-balance calculations show that up to 40% of the Ca budget and 65% of the Sr budget in some Hawaiian (Makapuu-stage Koolau) lavas are derived from recycled carbonates. Our finding demonstrates, for the first time with the application of Ca isotopes, that ancient recycled carbonates are important components of mantle plumes which feed some of the largest terrestrial volcanoes. Thus, recycling of carbonates into the mantle is an essential part of the global Ca and C cycles.     

Sulphur isotopic investigation of lower carboniferous vein deposits of the British Isles

Similar characteristics and age data suggest that the Pb + Zn vein deposits hosted by Lower Palaeozoic and Vendian strata of the British Isles form a genetically related group, coeval with the Lower Carboniferous carbonatehosted base-metal deposits of Ireland. Sulphur isotopic data demonstrate that there were separate sulphide and sulphate sulphur sources for the vein minerals. ³⁴S values from minerals in individual vein systems are consistent but there is a large variation between deposits, revealing distinctive local sulphur sources. The data suggests that sulphide sulphur (total range of values of ³⁴S_H2S of -6.5 to 18.62) was derived from the underlying strata while the sulphate (baryte) sulphur source (³⁴S_baryte mainly in the range 12 to 24) was groundwater or surface water that mixed with rising hydrothermal fluids in the upper reaches of the veins.     

Stable sulfur and nitrogen isotopic compositions of crude oil fractions from Southern Germany

Eleven samples of crude oil from the Molasse Basin of Southern Germany were fractionated and their contents of sulfur and nitrogen as well as the stable isotope compositions of these elements (${}^{34}\text{S}{}^{32}\text{S}$ and ${}^{15}\text{N}{}^{14}\text{N}$, resp.) investigated.According to the δ³⁴S determinations, all crude oils from the Tertiary base of the Western and Eastern Molasse belong to one oil family and differ significantly from the Triassic and Liassic oils in the Western Molasse.An enrichment of ³⁴S was observed with increasing polarity of crude oil fractions. The isotope distributions of sulfur in the polar constituents of the biodegraded oils from the sandstones of Ampfing, however, approach a homogeneous distribution.The nitrogen isotope distribution is rather uniform in Southern German oils. A regional differentiation can be recognized, although the overall isotopic variation is small. The δ¹⁵N values of the crudes and asphaltenes do not correlate.     

Molecular and stable carbon isotopic compositions of hopanoids in seep carbonates from the South China Sea continental slope

The lipid biomarkers of hopanoids in cold seep carbonates from the South China Sea continental slope were investigated by gas chromatography–mass spectrometer (GC–MS) and gas chromatography-isotope ratio-mass spectrometer (GC-ir-MS). The distribution of hopanes/hopenes shows a preference for the ‘biological’ 17β(H), 21β(H)-over the ‘geological’ 17α(H), 21β(H)-configuration. This interpretation is in agreement with the strong odd–even preference of long-chain n-alkanes in those samples, suggesting that the ββ hopanes may be the early diagenetic products of biohopanoids and the αβ, βα configurations of hopanes were mainly derived from allochthonous sources contributing to the organic matter of the carbonates. In terms of hopanoid acids, the C₃₀ to C₃₃ 17β(H), 21β(H)-hopanoid acids were detected with C₃₂ 17β(H), 21β(H)-hopanoid acid being the most abundant. However, there is a significant difference in stable carbon isotopic compostions of the C₃₂ 17β(H), 21β(H)-hopanoic acid among samples (−30.7‰ to −69.8‰). The δ¹³C values match well with the carbon isotopic compositions of SRB-derived iso-/anteiso-C_15:0 fatty acids in the samples, which strongly depend on the carbon utilization types by microbe. The most abundant compound of hopanols detected in the samples, C₃₀-17β(H), 21β(H)-hopanol, may be a good indicator of diagenetic product of type I methanotrophs. The molecular and carbon isotopic compositions of hopanoids demonstrate clearly that there is a combination contribution of both SRB and type I or type X methanotrophs to the source organism in the seep carbonates from the South China Sea continental slope.     

Stable isotopic compositions of waters in the karst environments of China: Climatic implications

A total of 117 water samples, including cave water, ground water, spring water and river water, collected from the monsoonal area of China have been analyzed for their H- and O-isotope composition. Overall, a δ¹⁸O–δD correlation is observed of δD = −4.45 + 6.6δ¹⁸O (R² = 0.90) and a significant evaporation effect observed for the southern sites. Average δ¹⁸O and δD site values generally correspond to those of precipitation in nearby cities, with correlations of δD = 2.18 + 7.23δ¹⁸O (R² = 0.95) for the sample sites and δD = 11.05 + 7.95δ¹⁸O (R² = 0.95) for the cities. The effects of rainfall amount and temperature on precipitation δ¹⁸O were calculated using a simplified theoretical model derived from the Rayleigh distillation equation, which demonstrated that the sign of δ¹⁸O_pvs. T correlation is dependent on precipitation intensity. The mean δ¹⁸O value of cave waters exhibit decreasing trends with increasing latitude and reveal a spatial pattern of positive correlation with annual mean temperature and precipitation, mainly reflecting isotopic fractionations in the moisture source traveling from the ocean side to the inland continent. This spatial pattern implies that the δ¹⁸O values recorded in the proxy climate records derived from speleothems might be influenced by shifts in monsoon boundary during the past, especially between glacial and interglacial intervals.     

稳定Sr-Nd同位素体系及其对传统放射成因锶钕同位素组成的影响

稳定Sr、Nd同位素是全新的体系,其重点关注自然过程中稳定Sr和Nd同位素分馏特征与控制机制。这方面的知识可以修正传统Rb Sr和Sm-Nd同位素体系中恒定的稳定Sr、Nd同位素组成的前提假设所带来的认知偏差,补充和完善其知识体系。介绍了稳定Sr、Nd同位素体系的基本概念,综述并点评了最新的分析技术进展,并对稳定Sr、Nd同位素分馏对传统的放射成因Sr、Nd同位素组成的影响进行评估,同时对这两个新的稳定同位素体系的潜在研究应用进行展望。     

Characterisation of chlorinated hydrocarbons from chlorine and carbon isotopic compositions: scope of application to environmental problems

A set of chlorinated hydrocarbons (TCE, PCE, DCM, 1,1,1-TCA, chloroform) provided by four manufacturers has been isotopically characterised for both C and Cl, using a new sensitive method. A very large range of δ¹³C (from −51.66 to −24.07‰/PDB) associated with a very large range of δ³⁷Cl (from −2.7 to +3.4‰/SMOC) was obtained. This range of δ³⁷Cl is much larger than that of inorganic Cl (±1‰ SMOC) and most individual solvents show a very distinct δ³⁷Cl compared to inorganic Cl isotopic signatures. Moreover, δ³⁷Cl/δ¹³C pairs are distinct from one solvent/manufacturer to another. In a δ¹³C versus δ³⁷Cl diagram, δ³⁷Cl / δ¹³C pairs show different trends for the products of a single manufacturer compared to another. This suggests that Cl isotopic compositions are probably highly fractionated during organic synthesis. The δ³⁷Cl values can be interpreted in terms of the probable manufacturing processes. Unlike the data published previously, with one exception, all the new results for samples reported here have positive δ³⁷Cl values which might differentiate natural Cl from that derived from degradation. This method has significant potential as a tool for investigating environmental pollution problems; in particular, it offers the possibility for validating models of transport and fate of pollutants.     

江西信江盆地晚白垩世塘边组成壤碳酸盐岩碳、氧同位素特征

利用古土壤成壤碳酸盐岩稳定同位素组成估算古代大气CO_2浓度,是当前古气候环境研究的重要手段。对采自江西信江盆地晚白垩世圭峰群塘边组的成壤碳酸盐岩碳、氧同位素测试表明,δ13C(PDB)值在-4.30‰~-2.10‰之间,平均值为-2.84‰。δ18O(PDB)值在-6.62‰~-1.14‰之间,平均值为-3.62‰。由Cerling经验公式估算出晚白垩世Campanian晚期约75 Ma的大气CO_2浓度在782~1 420 ppmv之间,平均值为1 181 ppmv,是当今大气CO_2浓度的2~4倍。因此,基于信江盆地塘边组成壤碳酸盐岩的大气CO_2浓度估算结果,可能指示了晚白垩世Campanian晚期存在一个大气CO_2浓度高峰值,反映了晚白垩世大气CO_2浓度的波动性。     

The post-Variscan development of the British Isles within a regional transfer zone influenced by orogenesis

The break-up of Pangaea after the Variscan Orogeny included rifting extending southwards from the Barents Sea via the Norwegian–Greenland Rift and into the North Sea, and northwards from the Central Atlantic. These two major rift systems interacted to form an approximately 1200-km-wide transfer zone across the British Isles, where a complex network of basins developed during the Mesozoic. Fault patterns were commonly controlled by reactivation of Precambrian, Caledonian and Variscan structures. The two main rift systems were unable to breach this regional transfer zone, where the crust had been thickened by the Caledonian and Variscan orogenies, until the Eocene. Breaching did not occur down the North Sea and through the English Channel because of Alpine contraction in NW Europe. Instead, breaching occurred around the west of Ireland and NW Scotland, so the British Isles remained connected to Europe rather than to the North American Plate.     

Terrestrial and freshwater carbonates in Hoxnian interglacial deposits, UK: micromorphology, stable isotopic composition and palaeoenvironmental significance

MIS 11 is often considered to be the best climatic analogue for the Holocene. Many studies have suggested, however, that it is a period of extreme climate warmth comparable in temperatures to the Middle and Late Pliocene. In Britain deposits of the Hoxnian interglacial are correlated to MIS 11 and multi-proxy techniques can be used to reconstruct the climate of this interglacial. Soil, groundwater and freshwater carbonates are common in Hoxnian deposits and the stable isotopic composition of these precipitates can be used to increase our understanding of MIS 11 environments in Britain. Carbonates from Marks Tey, Clacton, Swanscombe, Elveden and West Stow are studied, the stratigraphic context of which indicates that their formation is broadly synchronous (in the mid-Hoxnian, pollen zones Ho II to Ho III). The carbon isotopic composition of groundwater and pedogenic carbonates is typically depleted with respect to δ¹³C (ca −9 to −8‰ VPDB) reflecting uptake of plant respired CO₂ during water migration/recharge. The carbon isotopic composition of lacustrine carbonate is more enriched with respect to δ¹³C (ca 0-1‰VPDB) reflecting the equilibration of lake waters with atmospheric CO₂. The δ¹⁸O of groundwater and pedogenic carbonates is slightly more enriched than modern soil carbonates but not as enriched as soil carbonates formed under interglacials that were warmer than the Holocene (i.e. the Cromerian). The stable isotopic composition of Hoxnian carbonates does not, therefore, indicate that this interglacial was characterised by uniquely warm climates in the context of other Middle Pleistocene interglacials and the Holocene. This is contrary to many marine and littoral records from around the world but consistent with environmental records from Britain and Europe.     

The isotopic composition of Tertiary carbonates from the Mainz Basin: an example of isotopic fractionations in 'closed basins'

The carbon and oxygen isotopic composition of seventy-nine samples of biogenic carbonates from the Mainz Basin Tertiary (Oligocene and Lower Miocene) was analysed. Most samples were mollusc shells still consisting of aragonite. Assuming only small temperature effects, salinity trends derived from isotope data are consistent with palaeontological results from the region: a salinity cycle ranging from fresh water-brackish (Lower Oligocene) towards marine (Middle Oligocene) and brackish-fresh water (Upper Oligocene) was found. Within the Lower Miocene, a trend of decreasing salinities is suggested. Though the isotopic salinity trends coincide rather well with palaeontological salinities, the absolute oxygen isotope ratios indicate an unusual isotopic environment enriched in ¹⁸O. Isotope fractionation is explained by evaporation of a closed basin (Rupelton excluded) with fresh water influx from surrounding land areas in a subtropical climate. Enrichment in ¹⁸O by repeated evaporation processes is paralleled by increasing concentration of Sr. Increasing fresh water influx during the Oligocene is due to climatic changes with a trend of more humid conditions towards the younger rock strata.     

Stable carbon isotopic compositions of individual aromatic hydrocarbons as source and age indicators in oils from western Australian basins

The present study aims to establish the factors controlling the stable carbon isotopic compositions (δ¹³C) of individual aromatic hydrocarbons analysed by compound specific isotope analysis (CSIA) in crude oils from western Australian petroleum basins of varying age and facies type. This paper reports δ¹³C values of individual aromatic hydrocarbons, like alkylbenzenes, alkylnaphthalenes, alkylphenanthrenes and methylated biphenyls. The main aims are to confirm the origin (source) and age of these oils based on CSIA of selected aromatic compounds and to understand why the Sofer plot is ineffective in establishing the source of western Australian petroleum systems. The bulk δ¹³C of saturated and aromatic hydrocarbon fractions of crude oils have been previously used to differentiate sources, however, many Australian crude oils are not classified correctly using this method. The oils were classified as marine by the δ¹³C values of individual aromatic compounds and as terrigenous based on the bulk δ¹³C data (Sofer plot).The oils where the δ¹³C values of 1,6-DMN and 1,2,5-TMN isomers are most negative are indicative of a marine source, whereas oils with a less negative values for the 1,6-DMN and 1,2,5-TMN isomers are derived from marine source rocks that contain a significant terrigenous component. Similarly, oils with the least negative δ¹³C values for the 1-MP and 1,9-DMP isomers reflect varying inputs of terrigenous organic matter to the their marine source rocks. Plots of P/DBT and Pr/Ph concentration ratios versus δ¹³C values of DMP, 1,6-DMN, 1,2,5-TMN, 1-MP and 1,9-MP are constructed to establish the relative amount of terrigenous organic matter contributing to the source rock of a series of marine oils. The ratios of P/DBT and Pr/Ph plotted against the δ¹³C values of the aromatic isomers (such as 1,6-DMN, 1,2,5-TMN, 1-MP and 1,9-MP) provide a novel and convenient way to discriminate crude oils derived from different source rocks that contain varying amounts of marine and terrigenous organic matter.     

The first fossil mayfly nymph (Insecta: Ephemeroptera) from the British Isles

Mayflies are very rare in the British fossil record. The first nymph to be found, Schistonotorum wallisi gen. et sp. nov., is described from the non-marine Lower Cretaceous of southeast England. This Early Barremian find is from the Upper Weald Clay Formation at Smokejacks brickworks, Surrey. It is preserved as an adpression in concretionary sideritic ironstone from the upper insect bed exposed in the northeast face of the pit. The palaeoecological significance of this record is discussed.     

四川盆地寒武系含盐盆地演化及其找钾意义:来自碳氧同位素的证据

四川盆地寒武系岩盐分布广泛,面积约20万km2,主要分布于川东南、滇东北、渝东北、黔西北和鄂西北等地。含盐层位主要为中下寒武统(寒武系第二统与第三统)。不同地区的含盐层位不同,根据含盐盆地的分布与含盐系地层,将四川盆地大致划分为两个膏盐聚集区(次盐盆地):(1)川东南次盐盆地;(2)渝东北次盐盆地。川东南次盐盆地含盐层位为下寒武统清虚洞组(寒武系第二统第四阶中上部);渝东北次盐盆地含盐层位为中寒武统覃家庙组(寒武系第三统)。前人对四川盆地在岩相古地理与找钾水化学等方面进行了较多研究,但缺少寒武系钻孔样品的碳酸盐岩碳氧同位素分析其含盐盆地的演化研究。所以本文首次选取四川盆地寒武系3个具有代表性的钻孔岩屑样品(丁山1井、临7井与建深1井),对碳酸盐岩碳氧同位素组成进行对比分析,认为四川盆地寒武系碳酸盐岩δ13 C负漂移多与海退及生物灭绝事件有关,δ13 C的正漂移则多受海侵事件影响。四川盆地寒武纪海进、海退交替较为频繁,有利于组成良好的生储盖组合而形成油气藏。四川盆地下寒武统龙王庙阶(第四阶中上部)在川东南地区环境相对封闭,蒸发作用强烈,形成以江津—泸州为沉积中心的膏盐岩沉积区。中寒武世建深1井碳酸盐岩样品的δ13 C相对临7井较高,盐度也相对较高。结合四川盆地岩相古地理研究,认为从早寒武世至中寒武世古海水的浓缩方向有由川东南次盆地向渝东北次盆地演化的趋势,该认识对该区寒武系成盐找钾提供重要的依据,对成油气条件研究也有一定的参考价值。     

Morphological characters and multi-element isotopic signatures of carbonates from Chinese loess-paleosol sequences

Morphological characters and multi-element isotopic compositions of carbonates from the loess-paleosol sequences in Northwestern China are examined to explore the origin of the minerals. Samples are collected from various sections ranging from Holocene to 0.9 Ma within the sequences and fractions with grain sizes >45 and <2 μm are separated from the bulk soil and examined by SEM and TEM. The results show that the grains >45 μm exhibit an almost perfect spherical shape while those <2 μm are dominated by nano-rods having diameters of 30-50 nm and lengths of 0.3-2 μm, presumably indicating the detrital origin of the coarse fractions and the authigenic characters of the fine ones. Such implications are corroborated by the multi-elemental isotopic compositions of the carbonate minerals. A comparison of the δ¹³C and δ¹⁸O values between minerals and biologically originated samples indicates that the <2 μm fractions have a similar composition to those of coexisting land snail shells. Additional differences between the two size fractions also manifest in the ratios of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb, and ⁸⁷Sr/⁸⁶Sr. These results suggest the utility of fine carbonate particles in the soil profile in reconstructing a potentially higher resolution δ¹³C and δ¹⁸O time series to elucidate the paleoclimatic fluctuation in the Chinese Loess Plateau during Pleistocene. The discovery of the nano-rod calcite in Chinese loess, together with previous findings of the similar mineral form in Asian dust, strongly suggests the possibility that these highly reactive CaCO₃ form may alter the aerosol properties during transport.     

Iron and magnesium isotopic compositions of peridotite xenoliths from Eastern China

We present high-precision measurements of Mg and Fe isotopic compositions of olivine, orthopyroxene (opx), and clinopyroxene (cpx) for 18 lherzolite xenoliths from east central China and provide the first combined Fe and Mg isotopic study of the upper mantle. δ⁵⁶Fe in olivines varies from 0.18‰ to −0.22‰ with an average of −0.01 ± 0.18‰ (2SD, n = 18), opx from 0.24‰ to −0.22‰ with an average of 0.04 ± 0.20‰, and cpx from 0.24‰ to −0.16‰ with an average of 0.10 ± 0.19‰. δ²⁶Mg of olivines varies from −0.25‰ to −0.42‰ with an average of −0.34 ± 0.10‰ (2SD, n = 18), opx from −0.19‰ to −0.34‰ with an average of −0.25 ± 0.10‰, and cpx from −0.09‰ to −0.43‰ with an average of −0.24 ± 0.18‰. Although current precision (∼±0.06‰ for δ⁵⁶Fe; ±0.10‰ for δ²⁶Mg, 2SD) limits the ability to analytically distinguish inter-mineral isotopic fractionations, systematic behavior of inter-mineral fractionation for both Fe and Mg is statistically observed: Δ⁵⁶Fe_ol-cpx = −0.10 ± 0.12‰ (2SD, n = 18); Δ⁵⁶Fe_ol-opx = −0.05 ± 0.11‰; Δ²⁶Mg_ol-opx = −0.09 ± 0.12‰; Δ²⁶Mg_ol-cpx = −0.10 ± 0.15‰. Fe and Mg isotopic composition of bulk rocks were calculated based on the modes of olivine, opx, and cpx. The average δ⁵⁶Fe of peridotites in this study is 0.01 ± 0.17‰ (2SD, n = 18), similar to the values of chondrites but slightly lower than mid-ocean ridge basalts (MORB) and oceanic island basalts (OIB). The average δ²⁶Mg is −0.30 ± 0.09‰, indistinguishable from chondrites, MORB, and OIB. Our data support the conclusion that the bulk silicate Earth (BSE) has chondritic δ⁵⁶Fe and δ²⁶Mg.The origin of inter-mineral fractionations of Fe and Mg isotopic ratios remains debated. δ⁵⁶Fe between the main peridotite minerals shows positive linear correlations with slopes within error of unity, strongly suggesting intra-sample mineral-mineral Fe and Mg isotopic equilibrium. Because inter-mineral isotopic equilibrium should be reached earlier than major element equilibrium via chemical diffusion at mantle temperatures, Fe and Mg isotope ratios of coexisting minerals could be useful tools for justifying mineral thermometry and barometry on the basis of chemical equilibrium between minerals. Although most peridotites in this study exhibit a narrow range in δ⁵⁶Fe, the larger deviations from average δ⁵⁶Fe for three samples likely indicate changes due to metasomatic processes. Two samples show heavy δ⁵⁶Fe relative to the average and they also have high La/Yb and total Fe content, consistent with metasomatic reaction between peridotite and Fe-rich and isotopically heavy melt. The other sample has light δ⁵⁶Fe and slightly heavy δ²⁶Mg, which may reflect Fe-Mg inter-diffusion between peridotite and percolating melt.     

Elevated arsenic in deeper groundwater of the western Bengal basin, India: Extent and controls from regional to local scale

The deeper groundwater (depending on definition) of the Bengal basin (Ganges-Brahmaputra delta) has long been considered as an alternate, safe drinking-water source in areas with As-enrichment in near-surface groundwater. The present study provides the first collective discussion on extent and controls of elevated As in deeper groundwater of a regional study area in the western part of the Bengal basin. Deeper groundwater is defined here as non-brackish, potable (Cl⁻ ? 250 mg/L) groundwater available at the maximum accessed depth (∼80-300 m). The extent of elevated As in deeper groundwater in the study area seems to be largely controlled by the aquifer-aquitard framework. Arsenic-enriched deeper groundwater is mostly encountered north of 22.75°N latitude, where an unconfined to semi-confined aquifer consisting of Holocene- to early Neogene-age gray sand dominates the hydrostratigraphy to 300 m depth below land surface. Aquifer sediments are not abnormally enriched in As at any depth, but sediment and water chemistry are conducive to As mobilization in both shallow and deeper parts of the aquifer(s). The biogeochemical triggers are influenced by complex redox disequilibria. Results of numerical modeling and profiles of environmental tracers at a local-scale study site suggest that deeper groundwater abstraction can draw As-enriched water to 150 m depth within a few decades, synchronous with the advent of wide-scale irrigational pumping in West Bengal (India).     

A survey of the inorganic chemistry of bottled mineral waters from the British Isles

The inorganic chemistry of 85 samples of bottled natural mineral waters and spring waters has been investigated from 67 sources across the British Isles (England, Wales, Scotland, Northern Ireland, Republic of Ireland). Sources include boreholes, springs and wells. Waters are from a diverse range of aquifer lithologies and are disproportionately derived from comparatively minor aquifers, the most represented being Lower Palaeozoic (10 sources), Devonian Sandstone (10 sources) and Carboniferous Limestone (9 sources). The waters show correspondingly variable major-ion compositions, ranging from Ca–HCO₃, through mixed-cation–mixed-anion to Na–HCO₃ types. Concentrations of total dissolved solids are mostly low to very low (range 58–800 mg/L). All samples analysed in the study had concentrations of inorganic constituents well within the limits for compliance with European and national standards for bottled waters. Concentrations of NO₃–N reached up to half the limit of 11.3 mg/L, although 62% of samples had concentrations <1 mg/L. Concentrations of Ba were high (up to 1010 μg/L) in two spring water samples. Such concentrations would have been non-compliant had they been classed as natural mineral waters, although no limit exists for Ba in European bottled spring water. In addition, though no European limit exists for U in bottled water, should a limit commensurate with the current WHO provisional guideline value for U in drinking water (15 μg/L) be introduced in the future, a small number of groundwater sources would have concentrations close to this value. Two sources had groundwater U concentrations > 10 μg/L, both being from the Welsh Devonian Sandstone. The highest observed U concentration was 13.6 μg/L.     

Paleoenvironmental reconstruction from chemical and isotopic compositions of Permo-Pennsylvanian pedogenic minerals

Mineralogical and chemical analysis of Late Pennsylvanian and Early Permian paleosols from the eastern shelf of the Midland basin, north-central Texas, USA, are used to test hypothesized climate change in Late Paleozoic western equatorial Pangea, previously defined independently on the bases of sedimentologic and paleontologic proxies and climate models. The <0.2-μm size phyllosilicate fraction in the studied paleosols exhibits down-profile trends in mineralogy and chemical composition that are consistent with modern weathering profiles suggesting a dominantly pedogenic origin. A stratigraphic trend from kaolinite-dominated profiles in Upper Pennsylvanian paleosols to profiles dominated by smectite and hydroxy-interlayered 2:1 phyllosilicates in Lower Permian paleosols indicates a relatively rapid decrease in soil weathering and leaching in the latest Pennsylvanian followed by a more gradual decrease in leaching throughout the Early Permian. The chemical composition (cation ratios and exchange capacity) of these phyllosilicates further corroborates this shift toward less intensive leaching, presumably in response to climate change from humid to progressively more arid conditions.The phyllosilicates in the <0.2-μm size fraction and contemporaneous pedogenic calcites from the Permo-Pennsylvanian paleosols exhibit a long-term stratigraphic increase in their δ¹⁸O values of as much as ∼3.2‰ and ∼5.2‰, respectively. This long-term trend is consistent with a transition throughout the latest Pennsylvanian through Early Permian toward progressively more evaporatively enriched soil waters. Superimposed on the long-term trend is an apparent rapid enrichment (1.5 to 2‰) in phyllosilicate δ¹⁸O values immediately above the Pennsylvanian-Permian boundary. Observed oxygen isotope fractionation between the phyllosilicates and calcites within individual paleosols indicate isotopic disequilibrium between mineral pairs. This is attributed to a minor detrital component in the pedogenic clay-dominated phyllosilicate fraction coupled with the effects of seasonality of mineral formation. Inferred δ¹⁸O compositions of Late Paleozoic meteoric water (−2‰ to +4‰) are compatible with less intensive soil leaching under conditions of increasing aridity, possibly coupled with a shift in local precipitation from a continental source to a marine source.