Vulnerability of headwater catchment resources to incidences of <Superscript>210</Superscript>Pb excess and <Superscript>137</Superscript>Cs radionuclide fallout

Recent identification of elevated excess ²¹⁰Pb (≤302.6 mBq L⁻¹) and ¹³⁷Cs (≤111.3 mBq L⁻¹) activity in drinking water wells up to 20 m depth indicates some transport of airborne radionuclide fallout beyond soils in the Shaker Village catchment, Maine. Estimated airborne mass loading ²¹⁰Pb_ex fluxes of about 0.9 mBq m⁻³, canvass this headwater catchment and may be sufficient to pose risks to unprotected shallow wells. Inventories of ²¹⁰Pb_ex and ¹³⁷Cs in pond sediments indicate maximum median activities of 943 mBq g⁻¹ and 40.0 mBq g⁻¹, respectively. Calculated ²¹⁰Pb_ex fluxes in the catchment soils range from 0.62–0.78 Bq cm⁻² year⁻¹ and yield a mean residence time of near 140 years. Measured ¹³⁷Cs activity up to 51.1 mBq g⁻¹ occurs in sediments at least to 5 m depth. Assumed particle transport in groundwater with apparent ⁸⁵Kr ages less than 5 years BP (2005) may explain the correlation between these particle-reactive radionuclides and elevated activity in some drinking water wells.     

Geochemical signature of bottom sediments in the mixing zones of Ob and Yenisei waters with Kara Sea water

This paper reports the results of a study of the geochemistry of bottom sediments from the zones of mixing between the freshwater of the Ob and Yenisei rivers and the saline water of the Kara Sea by means of neutron activation analysis. Using separate datasets for the sediments of the Ob and Yenisei estuaries accumulated under identical facies conditions, some characteristic features of the distribution of a number of chemical elements (mostly lithophile group elements) were established. The differences between them were attributed to distinctive regional geological and geochemical features of the catchments of the Ob and Yenisei, which are inherited by the geochemical characteristics of terrigenous material transported to the sea. The choice of the most informative indicator elements and their grouping on the basis of the character of behavior demonstrated that bottom sediments of the Ob or Yenisei origin can be identified in the marine region studied using the geochemical characteristics of a small group of samples.     

Cosmogenic radionuclide <Superscript>7</Superscript>Be concentration in seven species of lichens and its correlation with <Superscript>40</Superscript>K, <Superscript>137</Superscript>Cs and <Superscript>226</Superscript>Ra

In this work, accumulation of cosmogenic radionuclide ⁷Be in seven species of lichens was determined using HPGe detectors in autumn season. Ramsar city which is located in the north of Iran as one of the high-level natural radiation areas in the world was considered. Lichen species represented good potential in accumulation of ⁷Be radionuclide. The foliose species of Xanthoria parietina with the highest activity concentration value of 112.8 ± 1.8 Bq kg^?1 was introduced as bioindicator for accumulation of ⁷Be radionuclide. Cladonia rangiformis species has got minimum concentration of 64.5 ± 0.8 Bq kg^?1. Also from thallus morphology viewpoint, results showed that ⁷Be accumulation in foliose species is higher than in fruticose and crustose lichens species. Also there was relatively large positive correlation between ⁷Be and ²²⁶Ra activity concentrations in lichens species.     

An analysis of naturally occurring radionuclides and <Superscript>137</Superscript>Cs in the soils of urban areas using gamma-ray spectrometry

This study of environmental radioactivity was carried out in the soils of an urban area. Naturally occurring gamma-emitting radionuclides and man-made ¹³⁷Cs were found in the soil profiles collected from four parks in the central Belgrade city area and the soil layer was examined every 10 cm and to a depth of 50 cm. Radioisotope activity concentrations (Bq kg^?1) in the samples of urban soil using the gamma-ray spectrometry method were in the range of 14–46 for ²³⁸U, 33–50 for ²²⁶Ra, 29–63 for ²¹⁰Pb, 1.2–3.4 for ²³⁵U, 28–50 for ²³²Th, 424–576 for ⁴⁰K and 0.7–35.8 for ¹³⁷Cs. Some of the basic physicochemical soil properties (pH, organic matter content, calcium-carbonate content, particle size distribution) were determined to investigate the impact on the vertical distribution of radionuclides. The results of this investigation showed that variations of activity concentration ratios of radionuclides that belong to the same (²³⁸U/²²⁶Ra) or different radioactive series (²³²Th/²²⁶Ra; ²³⁵U/²³⁸U), including ²¹⁰Pb/¹³⁷Cs ratios could well be explained by the properties of the soil. Alkaline pH reaction, the accumulation of organic matter in the uppermost and of carbonates in the deepest layers of urban soil had an effect on ²³⁸U/²²⁶Ra, and ²¹⁰Pb/¹³⁷Cs activity concentration ratio values, while ²³²Th/²²⁶Ra and partially ²³⁵U/²³⁸U ratios were associated with the particle sizes vertical distribution. A study of radionuclides in the samples of leaves of two deciduous tree species common for these parks was also conducted and ²¹⁰Pb and ⁴⁰K were found concentrated in leaves rather than other investigated radionuclides.     

Application of the <Superscript>137</Superscript>Cs tracer technique to study soil erosion of alpine meadows in the headwater region of the Yellow River

The ¹³⁷Cs tracer technique was used to study soil erosion of alpine meadow grassland in two small river basins in the headwater region of the Yellow River. The results show that the levels of ¹³⁷Cs in soil samples from this alpine meadow vegetation zone exhibit an exponential distribution, generally within a depth of approximately 20 cm. Due to strong winds, freeze-thaw cycles and water, soil erosion was found to be stronger on the upper slope than on the lower slope, and except for the slope crest, the intensity of soil erosion at other sites was as follows: upslope < midslope < downslope. There was a significant negative correlation between the intensity of soil erosion and the extent of alpine meadow vegetation cover (P < 0.01). The mean soil erosion modulus exhibited a linear reduction trend with an increase in vegetation cover, and the correlation coefficient R ² was ≥ 0.997. The higher the degradation degree of the alpine meadow grassland, the greater is the soil erosion. The mean erosion modulus in the severely degraded meadow zone was 2.23 times greater than the one in the slightly degraded zone, and the maximum erosion modulus reached 2.96 × 10⁶ kg/km²/a.     

Rapid migration of heavy metals and <Superscript>137</Superscript>Cs in alluvial sediments,Upper Odra River valley,Poland

The studies presented explore post-depositional changes of zinc, cadmium, lead, manganese and ¹³⁷Cs distribution in alluvial sediments accumulated in the upper Odra River valley in southern Poland. The rate of these changes was estimated by comparing metal and ¹³⁷Cs distributions in four vertical alluvial profiles with a history of river pollution and sediment deposition. The untypical ¹³⁷Cs distribution with peaks in the surface 40–60 cm and lower down, even at a depth of 2.5 m in strata deposited before the beginning of nuclear tests in 1954, indicates rapid post-depositional migration of this isotope from the surface and its retention in lower, less permeable layers. Moreover, the highest concentrations of lead, zinc and cadmium were found at a depth of 4 m in sediments accumulated in the mid-nineteenth century in spite of the growth of industrialization and the pollution of the Odra River with heavy metals until the end of the twentieth century. The post-depositional changes in heavy metals and ¹³⁷Cs are rapid in comparison with the slow element migration usually observed in uninundated soils. This difference is explained by the frequent and easy infiltration of polluted river water into the gravelly and sandy sediments present in the profiles.     

Mesozoic rift magmatism in the North Sea region: <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar geochronology of Scanian basalts and geochemical constraints

More than 100 volcanic necks composed of basanites and melanephelinites occur in Scania, southern Sweden, at the junction of two major tectonic lineaments, the Phanerozoic Sorgenfrei-Tornquist Zone (STZ) and the Proterozoic Protogine Zone. New ⁴⁰Ar/³⁹Ar isotope analyses of whole rock fragments of nine selected basalt necks suggest that the Mesozoic alkaline volcanism in the Scanian province commenced earlier than previously reported and comprised three separate volcanic episodes that span a total period of ca. 80 Myr: a first Jurassic (191–178 Ma), a second at the Jurassic/Cretaceous boundary (ca. 145 Ma), and a final middle Cretaceous episode (ca. 110 Ma). The new results allow for precise time correlations between eruption events in the Scanian and those in the North Sea volcanic provinces. The older, early Jurassic event in Scania is largely synchronous with that in the Egersund Basin and the Forties field whereas the event at ca. 145 Ma is correlated with activity in the Central Graben. These volcanic episodes also correlate in age with Kimmerian tectonic activity. Volcanic activity in the middle Cretaceous period has also been dated in the triple junction in the North Sea and offshore in the Netherland Sector. The correlation of basalt volcanism in Scania with the Egersund nephelinites strongly suggest that volcanism was triggered by repeated tectonic activity along the STZ. Geochemical data of alkaline mafic rocks in the Scanian and the North Sea volcanic provinces imply that different provinces have largely unique geochemical signatures in favour of a heterogeneous mantle in the North Sea volcanic region. However, basalts of different generations in one and the same province cannot be readily separated on the basis of geochemistry, suggesting that the same lithospheric mantle was the source of repeated volcanism over time in each province. The data suggest a low degree of melting of a volatile-bearing mantle lherzolite enriched in incompatible elements with the exception of the Forties basalts in the rift centre, produced by larger degree of melting and evolved by fractional crystallization.     

Extraction of potassium from biotite by Ba<Superscript>2+</Superscript>/K<Superscript>+</Superscript> ion exchange and the structural transformation

Potassium has been extracted successfully from biotite by Ba²⁺/K⁺ ion exchange. The potassium release rate increased along S-curve versus reaction time. The maximum of potassium release rate was about 96 %. Powder X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy were used to characterize the obtained samples to reveal the exchanging behavior and structural transformation. The results showed that after treated with Ba(NO₃)₂ four times the original biotite transformed to vermiculite-type hydrated Ba-mica. The (001) basal plane was expanded from 1.000 nm of biotite to 1.221 nm of hydrated Ba-mica. Because of the “vacancy effect,” the Ba²⁺ has two different statuses, causing the structural water vibration of vermiculite-type hydrated Ba-mica split. The edge of vermiculite-type hydrated Ba-mica was crimped compared with the flat edge of original biotite. The (001) basal plane of dehydrated Ba-mica was also split, supporting the “vacancy effect.”     

Detection of <Superscript>3</Superscript>H and <Superscript>85</Superscript>Kr in groundwater from arsenic-bearing crystalline bedrock of the Goose River basin,Maine

Presence of young groundwater (post-1950) in the Goose River basin is demonstrated with ³H and ⁸⁵Kr analyses. A total of 96 wells and four springs were sampled quarterly from 1999 to 2001 to determine the extent of any recent recharge and to what depth hydraulic continuity existed in the groundwatershed (33.3 km²). Recharge groundwater is less than 50 years in about 31% (³H) to 37% (⁸⁵Kr) of sampled wells and 75% of sampled springs. Young groundwater ages are recorded in wells up to 320 m in depth within fractured- and arsenic-bearing crystalline bedrock. Total arsenic 10 g L^–1 occurs significantly in drinking water with young groundwater flowing through the pumping well intervals. As_total occurs in 89% (⁸⁵Kr) to 93% (³H) of all wells with post-1950 groundwater ages. Young groundwater recharge and elevated geogenic arsenic were discovered only in the anatectic granitoids and migmatized country rock of the southwestern part of the Goose River basin.     

Factors of <Superscript>18</Superscript>O/<Superscript>16</Superscript>O fractionation in corundum estimated from the calculation of isotopic shifts on vibration frequencies

The β-factors of corundum were estimated on the basis of DFT calculations of vibrational frequency changes due to ¹⁶O–¹⁸O isotope substitution in a harmonic approximation using an all-electron Gaussian-type basis set and the B3LYP hybrid functional (the CRYSTAL program). Calculations were performed accounting for eight phonon wave vectors within the first Brillouin zone. The results are approximated by the relation 1000ln β _crn = 9.19874x–0.12326x ² + 0.00213x ³ (x = 10⁶/T(K)², 400 < T(K) < 1300), which can be used in isotope geochemical studies in combination with the known temperature effects on the β-factors of other phases.     

40^Ar／39^Ar Ages of Auriferous Quartz Veins from the Fengyang and Zhangbaling Regions and Their Geological Significance

Geotectonically the Fengyang and Zhangbaling regions belong to the North China craton and the Dabie-Sulu oragene, respectively. Neo-Archean gneiss and amphibolite and metamor-phosed sea-facies sodic volcanic rocks axe the main outcrops in the two regions, respectively. The Zhangbaling terrane strike-skipped along the Tancheng-Lujiang fault zone in Mesozoic and Cenozo-ic eras and got close to the Fengyang terrane. Mesozoic Yanshanian intrusions occur broadly in thetwo regions. Gold-beating quartz veins occur in the metamorphic rocks in the Fengyang region and in the granodiorite and metamorphosed sea-facies sodic volcanic rocks in the Zhanghaling region.Generally, the formation of the auriferous quartz veins involved three stages. At the first stage,gold-poor sulfide quartz veins were formed; at the second stage gold-rich quartz sulfide veins wereformed; and at the third stage gold-poor barite and/or carbonate veins were formed. The 40^Ar/29^Ar step-heating plateau ages of the first-stage and the second-stage quartz aggregates from the Zhuding, Maoshan and Shangeheng gold deposits range between 116.1 0.6 Ma and 118.3 0.5 Ma and are pretty close to their least apparent ages and isoehronal ages, respectively. All plat-eau, least apparent and isoehronal ages range between 113.4 0.4 Ma and 118.3 0.5 Ma,which are considered as the formation age range of the quartz. It is reasonable and reliable to takethe 40^Ar/39^Ar age range of the quartz as the formation age range of gold-bearing quartz veins onthe basis of spatial relationship between gold-bearing quartz veins and their country rocks. Thegold deposits in the two regions were formed in Aptian, Cretaceous, when the Tancheng-Lujiangfault zone moved as a normal fault with slightly right-lateral strike-skip, was extensional and expe-rienced very strong magnmtic process. It is shown that the magnmtic hydrothermal fluid is a veryimportant part of the gold ore-forming hydrothermal fluid in the Fengyang and Zhanghaling re-gions. The formation of the gold ore deposits in the Fengyang and Zhanghaling regions had genetic relations with the extensional movement of the Tancheng-Lujiang fault zone and magmatic activities and took place under the extensional dynamic condition in Late Cretaceous. Therefore, the exten-sional movement of the Tancheng-Lujiang fault zone presented the energy and space for magmatic and gold ore-forming processes.     

<Superscript>40</Superscript>Ar-<Superscript>39</Superscript>Ar age of a lava flow from the Bhimashankar Formation,Giravali Ghat,Deccan Traps

We report here a⁴⁰Ar-³⁹Ar age of 66.0 ± 0.9 Ma (2σ) for a reversely magnetised tholeiitic lava flow from the Bhimashankar Formation (Fm.), Giravali Ghat, western Deccan province, India. This age is consistent with the view that the 1.8–2 km thick bottom part of the exposed basalt flow sequence in the Western Ghats was extruded very close to 67.4 Ma.     

New <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar age constraints on cooling and unroofing history of the metamorphic host rocks (and igneous intrusion associates) from the Bulfat Complex (Bulfat area), NE-Iraq

The Northern Zagros Suture Zone (NZSZ), formed as a result of the collision between Arabian and Sanandaj-Sirjan microplate, is considered as part of the Zagros orogenic belt. NZSZ is marked by two allochthonous thrust sheets in upward stacking order: lower and upper allochthon. The Bulfat complex is a part of the upper allochthon or “Ophiolite-bearing terrane” of Albian-Cenomenion age (97–105 Ma). Voluminous highly sheared serpentinites associated with ophiolites occur within this upper allochthon. In addition, the Gemo-Qandil Group is characterized by gabbroic to dioritic Bulfat intrusion with a crystallization age spanning from ~45 to ~?40 Ma, as well as extensive metapelites with contact to the Walash-Naupurdam metavolcanic rocks. Due to the deformation in the Sanandaj-Sirjan Zone along the eastern side of the Iraqi segment of NZSZ, the Gemo-Qandil Group was regionally metamorphosed during late Cretaceous (~?80 Ma). This tectono-compressional dynamics ultimately caused an oscillatory deformation against Arabian continental margin deposits as well. During these events, gabbro-diorite intrusion with high-grade contact metamorphic aureoles occurred near Bulfat. Thus, there is an overlap between regional and contact metamorphic conditions in the area. The earlier metamorphic characteristic can be seen only in places where the latter contact influence was insignificant. Generally, this can only observed at a distance of more than 2.5 km from the contact. According to petrographic details and field observations, the thermally metamorphosed metapelitic units of the metasediment have been completely assimilated, with only some streaks of biotite and relicts of initial foliation. They strongly resemble amphibolite-grade slices from the regional metamorphic rocks in the region. Metapelitic samples far from the intrusion give similar biotite cooling ages as the intrusive rocks. Thus, they may be affected by the same thermal event. ⁴⁰Ar/³⁹Ar dating of biotite in metapelite rocks of Bulfat by step-wise heating with laser gave average weighted isotopic ages of 34.78?±?0.06 Ma. This is interpreted as crystallization/recrystallization age of biotite possibly representing the time of cooling and uplift history of the Bulfat intrusion. Cooling and exhumation rates for the Bulfat gabbro-diorite rocks were estimated as ~?400 °C/Ma and ~?3.3 mm/year respectively. According to petrographic details, field observations and Ar/Ar dating concerning the contact metamorphism near Bulfat due to the gabbro-diorite intrusion, no significant deformation is visible during exhumation processes after the Paleogene tectono-thermal event, indicating that isotopic ages of 34.78?±?0.06 Ma could mark the timing of termination of the island arc activity in the Ophiolite-bearing terrane (upper allochthon).