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EARTH SCIENCES (467 journals)                  1 2 3 | Last

Showing 1 - 200 of 371 Journals sorted alphabetically
Acta Geochimica     Hybrid Journal   (Followers: 7)
Acta Geodaetica et Geophysica     Hybrid Journal   (Followers: 2)
Acta Geodaetica et Geophysica Hungarica     Full-text available via subscription   (Followers: 2)
Acta Geophysica     Open Access   (Followers: 10)
Acta Geotechnica     Hybrid Journal   (Followers: 7)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 3)
Advances in High Energy Physics     Open Access   (Followers: 19)
Advances In Physics     Hybrid Journal   (Followers: 20)
Aeolian Research     Hybrid Journal   (Followers: 5)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 13)
Algological Studies     Full-text available via subscription   (Followers: 2)
Alpine Botany     Hybrid Journal   (Followers: 5)
AMBIO     Hybrid Journal   (Followers: 14)
Anales del Instituto de la Patagonia     Open Access   (Followers: 1)
Andean geology     Open Access   (Followers: 13)
Annales Henri Poincaré     Hybrid Journal   (Followers: 3)
Annales UMCS, Geographia, Geologia, Mineralogia et Petrographia     Open Access  
Annals of Geophysics     Open Access   (Followers: 13)
Annals of GIS     Hybrid Journal   (Followers: 24)
Annual Review of Marine Science     Full-text available via subscription   (Followers: 12)
Anthropocene     Hybrid Journal   (Followers: 4)
Anthropocene Review     Hybrid Journal   (Followers: 6)
Applied Clay Science     Hybrid Journal   (Followers: 5)
Applied Geochemistry     Hybrid Journal   (Followers: 14)
Applied Geomatics     Hybrid Journal   (Followers: 4)
Applied Geophysics     Hybrid Journal   (Followers: 8)
Applied Ocean Research     Hybrid Journal   (Followers: 8)
Applied Petrochemical Research     Open Access   (Followers: 3)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 36)
Arctic Science     Open Access   (Followers: 6)
Arctic, Antarctic, and Alpine Research     Full-text available via subscription   (Followers: 9)
Artificial Satellites : The Journal of Space Research Centre of Polish Academy of Sciences     Open Access   (Followers: 21)
Asia-Pacific Journal of Atmospheric Sciences     Hybrid Journal   (Followers: 20)
Asian Journal of Earth Sciences     Open Access   (Followers: 21)
Asian Review of Environmental and Earth Sciences     Open Access   (Followers: 2)
Atlantic Geology : Journal of the Atlantic Geoscience Society / Atlantic Geology : revue de la Société Géoscientifique de l'Atlantique     Full-text available via subscription   (Followers: 11)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 12)
Atmospheric and Climate Sciences     Open Access   (Followers: 28)
Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia     Hybrid Journal   (Followers: 11)
Boletim de Ciências Geodésicas     Open Access  
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 12)
Bragantia     Open Access   (Followers: 2)
Bulletin of Earthquake Engineering     Hybrid Journal   (Followers: 11)
Bulletin of Geosciences     Open Access   (Followers: 11)
Bulletin of the Lebedev Physics Institute     Hybrid Journal   (Followers: 1)
Bulletin of the Seismological Society of America     Full-text available via subscription   (Followers: 21)
Bulletin of Volcanology     Hybrid Journal   (Followers: 21)
Cadernos de Geociências     Open Access  
Canadian Mineralogist     Full-text available via subscription   (Followers: 6)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 22)
Carbonates and Evaporites     Hybrid Journal   (Followers: 3)
CATENA     Hybrid Journal   (Followers: 8)
Chemical Geology     Hybrid Journal   (Followers: 23)
Chemie der Erde - Geochemistry     Hybrid Journal   (Followers: 5)
Chinese Geographical Science     Hybrid Journal   (Followers: 5)
Chinese Journal of Oceanology and Limnology     Hybrid Journal   (Followers: 4)
Ciencia del suelo     Open Access   (Followers: 2)
Ciencias Espaciales     Open Access  
Climate and Development     Hybrid Journal   (Followers: 13)
Coastal Management     Hybrid Journal   (Followers: 25)
Cogent Geoscience     Open Access  
Comptes Rendus Geoscience     Full-text available via subscription   (Followers: 9)
Computational Geosciences     Hybrid Journal   (Followers: 15)
Computational Mathematics and Mathematical Physics     Hybrid Journal   (Followers: 3)
Computers and Geotechnics     Hybrid Journal   (Followers: 11)
Contemporary Trends in Geoscience     Open Access   (Followers: 3)
Continental Shelf Research     Hybrid Journal   (Followers: 9)
Contributions to Mineralogy and Petrology     Hybrid Journal   (Followers: 12)
Contributions to Plasma Physics     Hybrid Journal   (Followers: 4)
Coral Reefs     Hybrid Journal   (Followers: 18)
Cretaceous Research     Hybrid Journal   (Followers: 9)
Cybergeo : European Journal of Geography     Open Access   (Followers: 6)
Depositional Record     Open Access   (Followers: 1)
Developments in Geotectonics     Full-text available via subscription   (Followers: 3)
Developments in Quaternary Science     Full-text available via subscription   (Followers: 4)
Développement durable et territoires     Open Access   (Followers: 3)
Diatom Research     Hybrid Journal   (Followers: 3)
Doklady Physics     Hybrid Journal   (Followers: 1)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 13)
E&S Engineering and Science     Open Access  
E3S Web of Conferences     Open Access   (Followers: 1)
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 155)
Earth and Space Science     Open Access   (Followers: 14)
Earth Interactions     Full-text available via subscription   (Followers: 13)
Earth Science Frontiers     Full-text available via subscription   (Followers: 7)
Earth Science Research     Open Access   (Followers: 8)
Earth Surface Dynamics (ESurf)     Open Access   (Followers: 6)
Earth Surface Processes and Landforms     Hybrid Journal   (Followers: 20)
Earth System Dynamics     Open Access   (Followers: 9)
Earth System Dynamics Discussions     Open Access   (Followers: 6)
Earth's Future     Open Access   (Followers: 1)
Earth, Planets and Space     Open Access   (Followers: 71)
Earthquake Engineering and Engineering Vibration     Hybrid Journal   (Followers: 9)
Earthquake Science     Hybrid Journal   (Followers: 12)
Earthquake Spectra     Full-text available via subscription   (Followers: 21)
Ecohydrology     Hybrid Journal   (Followers: 12)
Ecological Questions     Open Access   (Followers: 6)
Electromagnetics     Hybrid Journal   (Followers: 8)
Energy Efficiency     Hybrid Journal   (Followers: 11)
Energy Exploration & Exploitation     Hybrid Journal   (Followers: 4)
Environmental Earth Sciences     Hybrid Journal   (Followers: 27)
Environmental Geology     Hybrid Journal   (Followers: 20)
Environmental Geosciences     Full-text available via subscription   (Followers: 5)
Environmental Geotechnics     Hybrid Journal   (Followers: 5)
Erwerbs-Obstbau     Hybrid Journal  
Estuaries and Coasts     Hybrid Journal   (Followers: 18)
Estuarine, Coastal and Shelf Science     Hybrid Journal   (Followers: 35)
Estudios Geográficos     Open Access  
European Journal of Mineralogy     Full-text available via subscription   (Followers: 16)
European Journal of Remote Sensing     Open Access   (Followers: 5)
Exploration Geophysics     Hybrid Journal   (Followers: 4)
Facies     Hybrid Journal   (Followers: 10)
Fieldiana Life and Earth Sciences     Full-text available via subscription   (Followers: 1)
Física de la Tierra     Open Access  
Folia Musei rerum naturalium Bohemiae occidentalis. Geologica et Paleobiologica     Open Access  
Folia Quaternaria     Open Access  
Forestry Chronicle     Full-text available via subscription   (Followers: 10)
Frontiers in Earth Science     Open Access   (Followers: 5)
Frontiers in Geotechnical Engineering     Open Access   (Followers: 3)
Frontiers of Earth Science     Hybrid Journal   (Followers: 9)
Fundamental and Applied Limnology / Archiv für Hydrobiologie     Full-text available via subscription   (Followers: 4)
GEM - International Journal on Geomathematics     Hybrid Journal   (Followers: 1)
Geo-Marine Letters     Hybrid Journal   (Followers: 7)
Geoacta     Open Access   (Followers: 4)
Geobiology     Hybrid Journal   (Followers: 10)
Geocarto International     Hybrid Journal   (Followers: 22)
Geochemistry : Exploration, Environment, Analysis     Hybrid Journal   (Followers: 8)
Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 32)
Geochimica et Cosmochimica Acta     Hybrid Journal   (Followers: 52)
Geochronometria     Hybrid Journal   (Followers: 3)
Geoderma Regional : The International Journal for Regional Soil Research     Full-text available via subscription   (Followers: 4)
Geodinamica Acta     Open Access   (Followers: 3)
Geodynamics & Tectonophysics     Open Access   (Followers: 2)
Geoenvironmental Disasters     Open Access   (Followers: 3)
Geofluids     Open Access   (Followers: 5)
Geoforum     Hybrid Journal   (Followers: 24)
Géographie physique et Quaternaire     Full-text available via subscription   (Followers: 1)
Geography and Natural Resources     Hybrid Journal   (Followers: 8)
Geoheritage     Hybrid Journal   (Followers: 1)
Geoinformatica Polonica : The Journal of Polish Academy of Arts and Sciences     Open Access  
Geoinformatics & Geostatistics     Hybrid Journal   (Followers: 11)
Geological Journal     Hybrid Journal   (Followers: 16)
Geological Magazine     Hybrid Journal   (Followers: 16)
Geology Today     Hybrid Journal   (Followers: 30)
Geology, Geophysics and Environment     Open Access   (Followers: 2)
Geomagnetism and Aeronomy     Hybrid Journal   (Followers: 3)
Geomatics, Natural Hazards and Risk     Hybrid Journal   (Followers: 11)
Geomechanics for Energy and the Environment     Full-text available via subscription   (Followers: 1)
GEOmedia     Open Access   (Followers: 1)
Geomorphology     Hybrid Journal   (Followers: 31)
Geophysical & Astrophysical Fluid Dynamics     Hybrid Journal   (Followers: 2)
Geophysical Journal International     Hybrid Journal   (Followers: 34)
Geophysical Prospecting     Hybrid Journal   (Followers: 7)
GeoResJ     Hybrid Journal  
Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards     Hybrid Journal   (Followers: 9)
Geoscience Canada : Journal of the Geological Association of Canada / Geoscience Canada : journal de l'Association Géologique du Canada     Full-text available via subscription   (Followers: 5)
Geoscience Data Journal     Open Access   (Followers: 2)
Geoscience Frontiers     Open Access   (Followers: 10)
Geoscience Letters     Open Access   (Followers: 1)
Geoscience Records     Open Access  
Geosciences     Open Access   (Followers: 2)
Geosciences Journal     Hybrid Journal   (Followers: 11)
Geoscientific Instrumentation, Methods and Data Systems     Open Access   (Followers: 4)
Geoscientific Model Development     Open Access   (Followers: 2)
Geostandards and Geoanalytical Research     Hybrid Journal   (Followers: 2)
Geosystem Engineering     Hybrid Journal   (Followers: 1)
Geotectonic Research     Full-text available via subscription   (Followers: 5)
Geotectonics     Hybrid Journal   (Followers: 7)
GISAP : Earth and Space Sciences     Open Access   (Followers: 2)
Glass Physics and Chemistry     Hybrid Journal   (Followers: 4)
Global and Planetary Change     Hybrid Journal   (Followers: 19)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 17)
Gondwana Research     Hybrid Journal   (Followers: 10)
GPS Solutions     Hybrid Journal   (Followers: 23)
Grassland Science     Hybrid Journal  
Ground Water     Hybrid Journal   (Followers: 36)
Ground Water Monitoring & Remediation     Hybrid Journal   (Followers: 19)
Groundwater for Sustainable Development     Full-text available via subscription   (Followers: 3)
Helgoland Marine Research     Open Access   (Followers: 3)
History of Geo- and Space Sciences     Open Access   (Followers: 4)
Hydrobiologia     Hybrid Journal   (Followers: 19)
Hydrogeology Journal     Hybrid Journal   (Followers: 22)
Hydrological Processes     Hybrid Journal   (Followers: 31)
Hydrology and Earth System Sciences     Open Access   (Followers: 31)
ICES Journal of Marine Science: Journal du Conseil     Hybrid Journal   (Followers: 53)
IEEE Journal of Oceanic Engineering     Hybrid Journal   (Followers: 13)
Indian Geotechnical Journal     Hybrid Journal   (Followers: 4)
Indonesian Journal on Geoscience     Open Access   (Followers: 2)
Interdisciplinary Environmental Review     Hybrid Journal   (Followers: 3)
International Geology Review     Hybrid Journal   (Followers: 16)
International Journal of Advanced Geosciences     Open Access   (Followers: 2)
International Journal of Advanced Remote Sensing and GIS     Open Access   (Followers: 39)
International Journal of Advancement in Earth and Enviromental Sciences     Open Access   (Followers: 5)
International Journal of Advancement in Remote Sensing, GIS, and Geography     Open Access   (Followers: 32)
International Journal of Applied Earth Observation and Geoinformation     Hybrid Journal   (Followers: 36)
International Journal of Coal Geology     Hybrid Journal   (Followers: 3)
International Journal of Disaster Risk Reduction     Hybrid Journal   (Followers: 18)
International Journal of Earth Sciences     Hybrid Journal   (Followers: 39)
International Journal of Earthquake and Impact Engineering     Hybrid Journal   (Followers: 4)
International Journal of Geo-Engineering     Open Access   (Followers: 3)

        1 2 3 | Last

Journal Cover Chemical Geology
  [SJR: 2.346]   [H-I: 145]   [23 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0009-2541
   Published by Elsevier Homepage  [3177 journals]
  • Geochemistry of sediments of the Peninsular rivers of the Ganga basin and
           its implication to weathering, sedimentary processes and provenance
    • Authors: Chinmaya Maharana; Deepika Srivastava; Jayant K. Tripathi
      Pages: 1 - 20
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): Chinmaya Maharana, Deepika Srivastava, Jayant K. Tripathi
      Geochemistry of the Himalayan rivers has been a major point of contention in sedimentary geochemistry because of its global impact on ocean chemistry and climate. Among the Himalayan rivers, the Ganga and its Himalayan catchment have been studied extensively. However, the Peninsular rivers constituting a significant part of the Ganga basin have not received much attention, heretofore. In the present geochemical study of the Peninsular river's sediments, we have found that the initial chemical weathering of rocks in the catchment produces texturally, mineralogically and geochemically diverse sediments and fluvial processes further segregate them into the geochemically contrasting coarse channel and fine-grained suspended sediments. The overbank sediments possess an intermediate texture and geochemistry, but more towards the suspended sediments. The sediment geochemistry data indicates that the Peninsular river's sediments show an increase in the weathering intensity from the west (Banas river) to the east (Son river) along the climate gradient, i.e., from the arid-semiarid to the sub-tropical condition. The higher chemical index of alteration (CIA) values of the Peninsular river's sediments than the Yamuna and Ganga river sediments reflect the control of weatherable lithology in the tectonically stable, low relief and subtropical climate condition. The Yamuna and Ganga river sediments with lower CIA values show more physical weathering in the tectonically active Himalaya. The suspended and overbank sediments of the Yamuna and Ganga rivers show an increase in their CIA values after the confluence of the Peninsular rivers, indicating the contribution of more weathered materials by the Peninsular rivers. It has been found that there is a geochemical split between the channel and suspended sediments of the Peninsular rivers for sharing different sources, i.e., the dominant contribution of felsic sources to the channel and mafic sources to the suspended sediments. The weathering geochemistry, trace element systematics, and REE patterns suggest that the dominant sources of the channel sediments of the Peninsular rivers are the felsic crystallines and sedimentary lithologies of the Aravalli range, Bundelkhand and Chhotanagpur granite and gneisses, and Vindhyan sandstones. Whereas, the mafic lithologies such as the Deccan traps and mafic components of the felsic lithologies appear to be the major sources of the suspended sediments. Within the range of intermediate composition, the overbank sediment chemistry reflects more contribution of the mafic sources except for the Ken which shows a higher contribution of the felsic sources. The geochemical split between the channel and suspended sediments of the Peninsular river's sediments for the different provenances indicates differential weathering of the Deccan basalts, Bundelkhand crystalline, and Vindhyan sedimentary rocks; and also the hydrodynamic control of the Peninsular rivers during erosion, transport, and deposition. However, the Himalayan rivers do not show such contrast between the channel and suspended sediments because of the higher physical weathering and sediment mixing in the high gradient topography of the Himalayan catchment.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.019
      Issue No: Vol. 483 (2018)
  • Visualization and quantification of Cd sorption to bacteria using confocal
           laser scanning microscopy and Cd-specific fluorescent probes
    • Authors: Clayton R. Johnson; Joshua D. Shrout; Jeremy B. Fein
      Pages: 21 - 30
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): Clayton R. Johnson, Joshua D. Shrout, Jeremy B. Fein
      Understanding metal sorption to bacteria is important for developing bioremediation strategies, for determining the fate of contaminants in ground water systems, and for defining controls on microbial metabolic processes in the environment. X-ray absorption spectroscopy (XAS) has been the only technique available for quantifying and mapping metal sorption to bacteria on an individual cell scale, but the XAS approach is time consuming and expensive, and quantitative mapping of the distribution of metals in complex samples is difficult with XAS. The development of metal-specific fluorescent probes, in conjunction with confocal laser scanning microscopy (CLSM), represents a novel and more effective approach for visualizing and quantifying biosorption. In this study, we test and calibrate the use of a commercially available Cd- and Pb-specific probe, Leadmium Green (LG), to quantify the distribution of Cd in bacteria-bearing systems. We have developed a treatment technique that uses a combination of the stock LG molecule and a chemically de-esterified form of the LG molecule (DELG) which enables us to quantify bacterial sorbed Cd. In this approach, we correlate the green fluorescence from LG and DELG with the fluorescence at a different wavelength of SYTO 63 cell stain which enables us to visualize and quantify bacterial cell Cd sorption on both a community and individual cell level. This approach, for the first time, yields a means of easily quantifying and visualizing metal adsorption onto individual bacterial cells which allows us to directly measure the distribution of Cd in bacteria-bearing environmental systems. In this study, we report the results of a range of control experiments that demonstrate the efficacy of this approach. We demonstrate that our chemical de-esterification of LG results in 100% conversion of the LG to the DELG form that is fluorescently active, and that untreated LG is not fluorescently active until it enters the cell. We also demonstrate that calibration curves for samples containing cells, LG, DELG, SYTO 63, and Cd can be developed. Our tests also demonstrate that neither LG nor DELG cause significant changes in sorption of Cd to bacterial cells. We present results from experiments showing that Cd sorption to bacteria is highly heterogeneous between cells, a result which differs from the previously held assumption of homogeneous sorption. The results of this study yield new insights into metal adsorption behavior in bacteria-bearing systems and our approach represents a powerful tool for quantifying the distribution of metals in complex realistic environmental samples.
      Graphical abstract image

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.020
      Issue No: Vol. 483 (2018)
  • The influence of organic complexation on Ni isotopic fractionation and Ni
           recycling in the upper soil layers
    • Authors: I.O. Zelano; C. Cloquet; F. Fraysse; S. Dong; N. Janot; G. Echevarria; E. Montargès-Pelletier
      Pages: 47 - 55
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): I.O. Zelano, C. Cloquet, F. Fraysse, S. Dong, N. Janot, G. Echevarria, E. Montargès-Pelletier
      The quantification of Ni isotopic fractionation induced by Ni binding to organic acids is a preliminary step to better constrain the mechanisms determining Ni isotopic fingerprint observed in surface soils, waters and plants, as well as the contribution of metal recycling during plant litter degradation. In this study, Ni isotopic fraction induced by reaction with small organic acids, e.g. citric and oxalic acids, and with soil purified humic acids (PHA) was investigated at different Ni-L ratio and pH conditions. The Donnan Membrane Technique was used to separate Ni bound to organic ligands from the free metal. Obtained results highlighted that Ni binding with carboxylic groups produces, in the adopted experimental conditions, a Δ60Nibond-free < 0.2‰. This value is not high enough to justify neither metal fractionation previously observed between soil and hyperaccumulators, nor the fractionation between different plant parts, e.g. roots and leaves. In parallel, leaf degradation experiments of two hyperaccumulating plants, where Ni is mainly present as Ni-citrate, were performed to simulate litter decomposition and to highlight the contribution of plants on Ni isotopic composition in surface soils and waters. In the case of the hyperaccumulator Alyssum murale, the degradation process did not induce any observable fractionation. On the contrary, during Rinorea bengalensis degradation experiment, a fractionation between Ni leached out in the first 10 days and between 10 and 30 days was observed (Δ60Ni10–30day = 0.20 ± 0.05‰). The observed fractionation evidenced a heterogeneous distribution of Ni within the leaves, and/or distinct chemical bonding to the leaf cells, and finally suggested the influence of the chemical bonding on Ni isotopic signature. Although a precise quantification of plant contribution on Ni isotopic signature in surface soils and waters is still not reached, our results produced important progress to elucidate the role of organic matter in regulating Ni isotopic fingerprint in surface layers.
      Graphical abstract image

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.023
      Issue No: Vol. 483 (2018)
  • The microbial cycling of phosphorus on long-term fertilized soil: Insights
           from phosphate oxygen isotope ratios
    • Authors: Qing-Fang Bi; Bang-Xiao Zheng; Xian-Yong Lin; Ke-Jie Li; Xi-Peng Liu; Xiu-Li Hao; Han Zhang; Jia-Bao Zhang; Deb P. Jaisi; Yong-Guan Zhu
      Pages: 56 - 64
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): Qing-Fang Bi, Bang-Xiao Zheng, Xian-Yong Lin, Ke-Jie Li, Xi-Peng Liu, Xiu-Li Hao, Han Zhang, Jia-Bao Zhang, Deb P. Jaisi, Yong-Guan Zhu
      Microorganisms mobilize phosphorus (P) from soil and make it available for plants. However, the role of microbial activity in soil P dynamics especially among different P pools is poorly understood largely due to methodological limitations. In this study, we analyzed the oxygen isotope ratios in phosphate (δ18OP) of sequentially extracted inorganic P (Pi) pools (H2O-Pi, NaHCO3-Pi, NaOH-Pi, and HCl-Pi) in a long-term agricultural research field in Henan, China with different fertilization histories and coupled with soil enzyme activity and P-cycling bacteria gene abundance studies. Results showed the dominant enzymes were alkaline phosphatase (APase) and phosphodiesterase (PDE), and the functional genes for P-cycling were bpp, cphy, phoX and pqqC. After long-term P fertilization, the δ18OP values of H2O-Pi, NaHCO3-Pi and NaOH-Pi pools approached to or achieved equilibrium, suggesting that the externally applied P was actively mobilized and cycled by soil microorganisms and speciated into different P pools. Based on the extent of isotope excursion among different Pi pools, the equilibrium fractionation oriented the source signature in the NaHCO3-Pi and NaOH-Pi pools, and HCl-Pi pool could be derived from P fertilizer but through multistep reactions, and mixed with the HCl-Pi from rock weathering product, which constituted HCl-Pi pool in the non-P treatments. Overall, the long-term P fertilization especially the balanced fertilization with nitrogen (N), P and potassium (K) was found to be beneficial for extensive utilization of soil P with abundant biological uptake and cell-internal Pi cycling. Variation partitioning analysis (VPA) indicated that the expression of functional genes may be stimulated to mobilize soil P under specific P pools distribution in this alkaline environment. Overall, our findings provide new insights to understand the roles of microbial activities in soil P biogeochemistry that are useful for agricultural P sustainability.
      Graphical abstract image

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.013
      Issue No: Vol. 483 (2018)
  • Improving paleohydrological and diagenetic reconstructions in calcite
           veins and breccia of a sedimentary basin by combining Δ47 temperature,
           δ18Owater and U-Pb age
    • Authors: Maurice Pagel; Magali Bonifacie; David A. Schneider; Cécile Gautheron; Benjamin Brigaud; Damien Calmels; Alexandre Cros; Bertrand Saint-Bezar; Philippe Landrein; Chelsea Sutcliffe; Donald Davis; Carine Chaduteau
      Pages: 1 - 17
      Abstract: Publication date: 20 March 2018
      Source:Chemical Geology, Volume 481
      Author(s): Maurice Pagel, Magali Bonifacie, David A. Schneider, Cécile Gautheron, Benjamin Brigaud, Damien Calmels, Alexandre Cros, Bertrand Saint-Bezar, Philippe Landrein, Chelsea Sutcliffe, Donald Davis, Carine Chaduteau
      In sedimentary basins, the precise temperature and timing at which relatively shallow (<60°C) diagenetic and tectonic events occur are poorly recorded by classic geothermometers and low-temperature thermochronometers. In this study, we apply a methodology coupling carbonate clumped isotope Δ47 thermometry with U-Pb geochronology. Calcite breccias and veins from the border of the Gondrecourt graben (eastern Paris Basin, France), in Kimmeridgian limestones, were observed by optical microscopy and cathodoluminescence. They display Δ47 values that are identical within uncertainties (ranging from 0.621 to 0.635‰), implying very uniform calcite deposition temperatures averaging 44±4°C for the three investigated zones. When Δ47 temperatures are combined with the measured oxygen isotope composition of the calcite (δ18Ocal between −9.0‰ and −8.3‰V-PDB), one can calculate the δ18O of the water (δ18Owater) from which these cement breccia and vein calcite precipitated. The δ18Owater are very uniform (average of −4.5±1‰V-SMOW) and overall are consistent with a meteoric origin, however with a slight 18O–enrichment via interaction with limestones prior to precipitation. U-Pb dating by LA-ICP-MS yields a model age for three hydraulic breccias at 43–42Ma and an age at 35Ma for calcite veining obtained from a single vein sample. When considering the geothermal gradient, the surface temperature during the Eocene and erosion, the temperatures obtained by Δ47 thermometry suggest that there were hot waters circulating from the Middle Jurassic sequences below. Additional geochemical data (δ18Ocal, δ13Ccal, Rare Earth Elements, Mg, Mn and Sr compositions from a larger set of calcite breccias and veins from the area, together with published δD values of fluid inclusions) allow further characterization of the fluid from which the calcite phases precipitated. Notably, the whole suite of calcite shows a slight decrease in both δ18Ocal and δ13Ccal (δ18Ocal between −8.3‰ and −9.9‰V-PDB, δ13Ccal between 2.9‰ and 0.9‰V-PDB) and in Mg and Mn contents from breccia to veins, indicative of higher water:rock ratios during the vein stage and leaching of different source limestones. More broadly, this study demonstrates the potential improvement in diagenetic and paleohydrological research by combining U-Pb dating from the same calcite crystals as those analyzed for stable and clumped isotopes.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2017.12.026
      Issue No: Vol. 481 (2018)
  • The use of dithiothreitol for the quantitative analysis of elemental
           sulfur concentrations and isotopes in environmental samples
    • Authors: Martin R. Kurek; William P. Gilhooly; Gregory K. Druschel; Molly D. O'Beirne; Josef P. Werne
      Pages: 18 - 26
      Abstract: Publication date: 20 March 2018
      Source:Chemical Geology, Volume 481
      Author(s): Martin R. Kurek, William P. Gilhooly, Gregory K. Druschel, Molly D. O'Beirne, Josef P. Werne
      Determining the concentration and isotopic composition of elemental sulfur in modern and ancient environments is essential to improved interpretation of the mechanisms and pathways of sulfur utilization in biogeochemical cycles. Elemental sulfur can be extracted from sediment or water samples and quantified by converting to hydrogen sulfide. Alternatively, elemental sulfur concentrations can themselves be analyzed using HPLC and other methodologies; however, the preparation and analysis times can be long and these methods are not amenable to stable isotopic analysis. Current reduction methods involve the use of costly and specialized glassware in addition to toxins such as chromium chloride or cyanide to reduce the sulfur to hydrogen sulfide. The novel reduction method presented here uses dithiothreitol (DTT) as a less toxic reducing agent to obtain both elemental sulfur concentrations and isotopic composition from the same sample. The sample is dissolved in an aqueous or organic liquid medium and upon reaction with DTT, the elemental sulfur is volatilized as hydrogen sulfide and collected in a sulfide trap using an inexpensive gas extraction apparatus. The evolved sulfide concentrations can easily be measured for concentration, by absorbance spectrophotometery or voltammetry techniques, and then analyzed for sulfur isotopic composition. The procedure is quantitative at >93% recovery to dissolved elemental sulfur with no observed sulfur isotope fractionation during reduction and recovery. Controlled experiments also demonstrate that DTT is not reactive to sulfate, sulfite, pyrite, or organic sulfur.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.014
      Issue No: Vol. 481 (2018)
  • 4D multi-scale imaging of reactive flow in carbonates: Assessing the
           impact of heterogeneity on dissolution regimes using streamlines at
           multiple length scales
    • Authors: H.P. Menke; C.A. Reynolds; M.G. Andrew; J.P. Pereira Nunes; B. Bijeljic; M.J. Blunt
      Pages: 27 - 37
      Abstract: Publication date: Available online 31 January 2018
      Source:Chemical Geology
      Author(s): H.P. Menke, C.A. Reynolds, M.G. Andrew, J.P. Pereira Nunes, B. Bijeljic, M.J. Blunt
      We have experimentally investigated the impact of heterogeneity on the dissolution of two limestones, characterised by distinct degrees of flow heterogeneity at both the pore and core scales. The two rocks were reacted with reservoir-condition CO2-saturated brine at both scales and scanned dynamically during dissolution. First, 1 cm long 4 mm diameter cores were scanned during reactive flow with a 4 μm voxel size between 10 and 71 times using 4D X-ray micro-tomography (μ-CT) over the course of 90 min. Second, 3.8 cm diameter, 8 cm long cores were reacted at the same conditions inside a reservoir-condition flow apparatus and imaged using a medical-grade X-ray computed tomography scanner (XCT). Each sample was imaged ~13 times over the course of 90 min at a 250 × 250 × 500 μm resolution. These larger cores were then scanned inside a μ-CT at a 27 μm voxel size to assess the alteration pore-space heterogeneity after reaction. Both rock types exhibited channel widening at the mm scale and progressive high porosity pathway dissolution at the cm scale. In the more heterogeneous rock, dissolution was more focussed and progressed along the direction of flow. Additionally, the dissolution pathways contained a distinct microstructure captured with the μ-CT that was not visible at the resolution of the XCT, where the reactive fluid had not completely dissolved the internal pore-structure. This microstructure was further analyzed by performing a direct simulation of the flow field and streamline tracing on the image voxels. We found that at the larger scales the interplay between flow and reaction significantly affects flow in the unreacted regions of the core. When flow is focussed in large reacted channels, this focusing is carried through to the unreacted parts of the rock where flow continues to be confined to preferential pathways after passing the reaction front. This focussing effect is greater with increasing pore space heterogeneity indicating that the representative elementary volume (REV) for dissolution is far greater than the dissolution front itself. This study of scale dependence using in situ 4D tomography provides insight into the mechanisms that control local reaction rates at the mm and cm scales. Furthermore, this work suggests that under these conditions at larger scales it is likely to be structural heterogeneity that dominates the pattern of dissolution and therefore the evolution of high permeability pathways.

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.01.016
      Issue No: Vol. 481 (2018)
  • Variable Ni isotope fractionation between Fe-oxyhydroxides and
           implications for the use of Ni isotopes as geochemical tracers
    • Authors: Bleuenn Gueguen; Jeffry V. Sorensen; Stefan V. Lalonde; Jasquelin Peña; Brandy M. Toner; Olivier Rouxel
      Pages: 38 - 52
      Abstract: Publication date: Available online 3 February 2018
      Source:Chemical Geology
      Author(s): Bleuenn Gueguen, Jeffry V. Sorensen, Stefan V. Lalonde, Jasquelin Peña, Brandy M. Toner, Olivier Rouxel
      Nickel (Ni) isotopes have recently emerged as a new biogeochemical tracer in marine environments, but our understanding of the mechanisms of Ni isotope fractionation in natural systems with regards to its fractionation by mineral surfaces is incomplete. This study aims to provide experimental constraints on Ni isotope fractionation during adsorption to goethite and 2-line ferrihydrite, two Fe minerals that vary in terms of distinct crystalline properties. We conducted two types of adsorption experiments: one with variable pH (5.0 to 8.0) and constant initial Ni concentration, one at a constant pH of 7.7 and variable initial Ni concentrations. Isotopic measurements were made on both the solid phase and the supernatant solutions in order to determine the Ni isotope fractionation factors (Δ60/58Nimin-aq = δ60/58Nimin − δ60/58Niaq) between the mineral and aqueous phases. Our results show preferential adsorption of lighter Ni isotopes during adsorption of Ni to Fe oxyhydroxides presumably under conditions of near equilibrium conditions. Adsorption to goethite generates the greatest fractionation, with Δ60/58Nimin-aq = −0.77 ± 0.23‰ (n = 14, 2sd), whereas adsorption to 2-line ferrihydrite samples yield Δ60/58Nimin-aq = −0.35 ± 0.08‰ (n = 16, 2sd). Using Ni K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, we found that Ni forms an inner-sphere complex and that its coordination environment does not vary significantly with pH nor with surface loading. In addition, we found no evidence of Ni incorporation into the mineral. We suggest that the more than two-fold increase in Ni isotope fractionation in goethite relative to 2-line ferrihydrite is due to the lower Ni-Fe coordination number in the second shell, which results in the formation of a weaker surface complex and thus favors the adsorption of lighter Ni isotopes. These results show that Ni isotope fractionation during sorption by Fe-oxyhydroxides is dependent on mineralogy, which has important implications for the use of Ni isotopes as environmental tracers and the interpretation of their record in sedimentary rocks.

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.01.023
      Issue No: Vol. 481 (2018)
  • Neptunium(V) sorption to vadose zone sediments: Reversible, not readily
           reducible, and predictable based on Fe-oxide content
    • Authors: Brian A. Powell; Daniel I. Kaplan; Todd M. Miller
      Pages: 53 - 64
      Abstract: Publication date: Available online 31 January 2018
      Source:Chemical Geology
      Author(s): Brian A. Powell, Daniel I. Kaplan, Todd M. Miller
      Neptunium (Np) is among the key risk-drivers at the Savannah River Site's (SRS) low-level waste disposal facility located in South Carolina. A series of studies were undertaken to identify and to model the key geochemical processes controlling Np sorption to SRS vadose zone sediments. The approach was to conduct Np(V) laboratory batch and flow studies using two sediments representing end-member depositional facies recovered beneath the disposal facility. Baseline distribution coefficients (K d values; Np concentration ratio of sediment:porewater) were 9.05 ± 0.61 L kg−1 and 4.26 ± 0.24 L kg−1 for the clayey and sandy end-member sediments, respectively. The addition of natural organic matter (NOM) to the sediment resulted in only a two fold increase in the K d values, most likely due to the formation of ternary sediment-NOM-Np complexes. None of the reduction treatments (ascorbic acid, dithionite, zero valent iron, hydrogen peroxide, and anaerobic atmosphere), including some long-term (71-day) equilibration experiments, resulted in significant increases in K d values. This indicated that little to no reduction of Np(V) to the more strongly sorbing Np(IV) occurred. Among the key novel findings in this research was that batch desorption tests and stop-flow stir-cell kinetic experiments indicated that the Np(V) sorption was completely reversible. These observations were used to develop a simple conceptual model describing Np(V) sorption. The conceptual model described NpO2 + reversibly complexation to iron oxide coatings on the sediments. The model was successfully applied without any adjustable parameters to an independent set of experimental data, requiring only the dithionite-extractable Fe concentration from the independent dataset. There is no standard approach for quantifying reactive sorption site concentrations on composite materials (e.g., soils and sediments). In this study we proposed such a method based on an operationally defined fraction of the extractable iron. This parameterization approach was calibrated with two sediments then used to blindly and successfully predict sorption on another end-member soil. The successful modeling approach taken in this work 1) identified key reactions that are or are not influencing the system to develop a simple but appropriate conceptual model and 2) calibrated the fraction of extractable iron required for surface site density determination and used the calibrated model for blind predictions. This modeling approach could be used for other composite materials to allow for comparisons of the fraction of surface reactive extractable metals.
      Graphical abstract image

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.01.026
      Issue No: Vol. 481 (2018)
  • Iron isotope fractionation during uptake of ferrous ion by phytoplankton
    • Authors: Ruoyu Sun; Baoli Wang
      Pages: 65 - 73
      Abstract: Publication date: Available online 31 January 2018
      Source:Chemical Geology
      Author(s): Ruoyu Sun, Baoli Wang
      The uptake of iron (Fe) by phytoplankton is an important pathway that drives the global Fe biogeochemical cycle. However, limited information is available regarding the resulting Fe isotope signatures during this metabolic processes. Here, two algal species Chlorella pyrenoidosa and Chlamydomonas reinhardtii were cultured in a medium spiked with FeSO4 to study their ability to fractionate Fe isotopes. We quantified the total cellular and intracellular Fe, and measured their isotope compositions. The amounts and isotope compositions of extracellular Fe were estimated by mass balance. We found that the intracellular Fe of algae in concentration-gradient experiments was enriched in the heavier isotopes relative to the FeSO4 solutions, up to 3‰ in δ56Fe, suggesting the heavier Fe isotopes are preferably taken up by the algae. However, the intracellular Fe of algae in time-course experiments showed inconsistent fractionation patterns, either enriching or depleting heavier Fe isotopes. Extracellular Fe was isotopically variable from −2.5‰ to 1.9‰ in δ56Fe relative to the FeSO4 solutions, likely representing a mixture of FeII and FeIII adsorbed on the cell surface. Additionally, the variation of intracellular δ56Fe values appears to be dependent of the intracellular Fe fractions, enriching heavier Fe isotopes at the lower intracellular Fe fractions. Our observations not only highlight the potential of using Fe isotopes as the tracer of biological Fe cycles, but also have important implications on the Fe metabolic pathways of algae.
      Graphical abstract image

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.01.031
      Issue No: Vol. 481 (2018)
  • Comparison of δ53CrCr(VI) values of contaminated groundwater at two
           industrial sites in the eastern U.S. with contrasting availability of
           reducing agents
    • Authors: Martin Novak; Ondrej Sebek; Vladislav Chrastny; Lucas A. Hellerich; Alexandre Andronikov; Eva Martinkova; Juraj Farkas; Petra Pacherova; Jan Curik; Marketa Stepanova; Eva Prechova; Marie Houskova; Vera Zoulkova; František Veselovsky; Irena Svobodova; Petra Janotova; Arnost Komarek
      Pages: 74 - 84
      Abstract: Publication date: Available online 31 January 2018
      Source:Chemical Geology
      Author(s): Martin Novak, Ondrej Sebek, Vladislav Chrastny, Lucas A. Hellerich, Alexandre Andronikov, Eva Martinkova, Juraj Farkas, Petra Pacherova, Jan Curik, Marketa Stepanova, Eva Prechova, Marie Houskova, Vera Zoulkova, František Veselovsky, Irena Svobodova, Petra Janotova, Arnost Komarek
      Natural attenuation of groundwater contaminated by toxic hexavalent chromium [Cr(VI)] was studied at two industrial sites in the eastern U.S. Concentration and isotope composition of the residual Cr(VI) were determined at site A in Connecticut whose aquifer was polluted by electroplating solutions between 1930 and 1995, and at site B in New Jersey whose aquifer was polluted by soluble chromium-processing wastes between 1911 and 1963. Site A was characterized by lower mean Cr(VI) concentrations (2 mg L−1) and lower mean δ53CrCr(VI) values (1.84‰) in groundwater than site B (200 mg L−1 and 2.89‰, respectively). δ53CrCr(VI) values were strongly positively correlated with dissolved organic carbon (DOC; p = 0.002), but not with dissolved ferrous iron [Fe(II)], or divalent manganese [Mn(II)], indicating that DOC may have played a major role in spontaneous reduction of the mobile carcinogenic Cr(VI) to immobile non-toxic Cr(III). At site B, the supply of DOC may be nearly unlimited, due to the presence of a buried organic meadow mat at a depth of six meters below the ground surface. At site A, contaminated groundwater has been extracted and treated since 1995. The mean δ53CrCr(VI) values of the residual aqueous contamination at site A significantly decreased over the past 15 years (p < 0.05), possibly suggesting re-oxidation and remobilization of previously precipitated pollutant Cr.

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.01.033
      Issue No: Vol. 481 (2018)
  • Using statolith elemental signatures to confirm ontogenetic migrations of
           the squid Doryteuthis gahi around the Falkland Islands (Southwest
    • Authors: Jessica B. Jones; Alexander I. Arkhipkin; Andy L. Marriott; Graham J. Pierce
      Pages: 85 - 94
      Abstract: Publication date: Available online 2 February 2018
      Source:Chemical Geology
      Author(s): Jessica B. Jones, Alexander I. Arkhipkin, Andy L. Marriott, Graham J. Pierce
      The Patagonian long-finned squid Doryteuthis gahi is an abundant commercial species within Falkland Island waters. The population consists of two temporally distinct spawning cohorts, inferred to have markedly different patterns of migration and timings of ontogenetic events. Ontogenetic migrations of each cohort were confirmed by analysis of the chemical composition of statoliths collected from both cohorts in two consecutive years. Trace element concentrations were quantified using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), to determine temporal and cohort-specific variation. Individual ablation craters, ablated in a transect from the nucleus to the rostrum edge, were aged to produce high-resolution elemental chronologies. Generalized additive mixed models (GAMM) indicated that cohort and life history stage had a significant effect on Sr/Ca and Ba/Ca ratios. Sr/Ca and Ba/Ca ratios were both negatively correlated with near-bottom water temperature, with Ba/Ca also potentially correlated to depth. Statolith elemental chronologies have useful applications as natural tags, discriminating between spawning cohorts.

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.01.034
      Issue No: Vol. 481 (2018)
  • Archean magmatic-hydrothermal fluid evolution in the Quadrilátero
           Ferrífero (SE Brazil) documented by B isotopes (LA MC-ICPMS) in
    • Authors: Capucine Albert; Cristiano Lana; Axel Gerdes; Mathias Schannor; Francesco Narduzzi; Gláucia Queiroga
      Pages: 95 - 109
      Abstract: Publication date: Available online 2 February 2018
      Source:Chemical Geology
      Author(s): Capucine Albert, Cristiano Lana, Axel Gerdes, Mathias Schannor, Francesco Narduzzi, Gláucia Queiroga
      In the Archean Quadrilátero Ferrífero district (SE Brazil), tourmaline occurs as a major constituent in a leucogranitic intrusion and numerous pegmatitic/aplitic veins within magmatic basement complexes, as well as in quartzo-feldspathic veins, in quartz-tourmaline rocks (tourmalinites) and as disseminated grains in the surrounding greenstone belt metasediments. The chemical and boron isotope composition of these tourmalines was analysed by electron microprobe and LA MC-ICP-MS to determine the origin of the fluids involved and to shed light on the hydrothermal evolution of the region. The tourmalines exhibit an overall decrease in Fe/(Fe + Mg) ratio and a net increase in Cr (up to 0.75 wt%) from tourmaline hosted in the leucogranite, the quartzo-feldspathic veins, the tourmalinites to the disseminated grains in the schists. These variations mirror the bulk composition of the host schists, and illustrate a strong protolith control on tourmaline major element composition. The full range of tourmaline δ11B is from −27.1 to −9.2‰, with a major cluster between −12 and −19‰, which includes the magmatic tourmaline in the leucogranite (−15.2 to −12.5‰). Most of these isotope compositions can be reconciled with a model involving tourmaline growth from late-stage exsolved magmatic fluids percolating through the magmatic basement and into the nearby metasediments. This model agrees well with the trends of major element compositions, as well as with the critical observation that tourmaline occurrence is restricted to the vicinity of the basement complexes. δ11B values lower than ~−19‰ in our dataset are beyond the reach of isotope fractionation during magmatic fluid exsolution and temperature decrease, and suggest the presence of a distinct fluid component. We propose that an isotopically light fluid was released from mica breakdown in the country rocks during local upper amphibolite facies metamorphism in the dome border shear zone.

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.02.002
      Issue No: Vol. 481 (2018)
  • Cadmium isotopic evidence for the evolution of marine primary productivity
           and the biological extinction event during the Permian-Triassic crisis
           from the Meishan section, South China
    • Authors: Yuxu Zhang; Hanjie Wen; Chuanwei Zhu; Haifeng Fan; Christophe Cloquet
      Pages: 110 - 118
      Abstract: Publication date: 20 March 2018
      Source:Chemical Geology, Volume 481
      Author(s): Yuxu Zhang, Hanjie Wen, Chuanwei Zhu, Haifeng Fan, Christophe Cloquet
      Cadmium (Cd) isotopic compositions in seawater are important parameters for tracing the biogeochemical cycling of Cd in modern oceans and may be used as a direct proxy for nutrient utilization by phytoplankton and an indirect proxy for primary productivity. In this study, we measured the stable Cd isotope ratios (δ114Cd) of marine sedimentary carbonates from the Meishan section in Changxing County of Zhejiang Province, South China, the Global Stratotype Section and Point (GSSP) of the Permian-Triassic Boundary (PTB). The results suggest that the inferred marine primary productivity recorded in the marine carbonates from the Late Permian (i.e., before the mass extinction) was high and relatively stable (the δ114/110Cd values of carbonates range from +0.31‰ to +0.60‰; after correction for salinity-controlled fractionation into inorganic calcite, the δ114/110Cd values of palaeo-seawater range from +0.47‰ to +0.79‰). During the mass extinctions, the δ114/110Cd values of carbonates abruptly decreased at the beginning of each episode of mass extinction, suggesting that the primary productivity of the palaeo-ocean declined before each episode of extinction events at the PTB. We suggest that the mass extinction events at the PTB in the Meishan section could be a ripple effect due to the destruction of primary producers at the base of the food chain in the palaeo-ocean ecosystem.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.005
      Issue No: Vol. 481 (2018)
  • Multiproxy geochemical and isotope stratigraphy records of a
           Neoproterozoic Oxygenation Event in the Ediacaran Sete Lagoas cap
           carbonate, Bambuí Group, Brazil
    • Authors: Fabrício A. Caxito; Robert Frei; Gabriel J. Uhlein; Tatiana Gonçalves Dias; Trygvi Bech Árting; Alexandre Uhlein
      Pages: 119 - 132
      Abstract: Publication date: Available online 3 February 2018
      Source:Chemical Geology
      Author(s): Fabrício A. Caxito, Robert Frei, Gabriel J. Uhlein, Tatiana Gonçalves Dias, Trygvi Bech Árting, Alexandre Uhlein
      Graphical abstract image

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.02.007
      Issue No: Vol. 481 (2018)
  • Uranium isotope geochemistry in modern coastal sediments: Insights from
           Toulon Bay, France
    • Authors: Duc Huy Dang; R. Douglas Evans; Wei Wang; Dario Omanović; Amonda El Houssainy; Véronique Lenoble; Jean-Ulrich Mullot; Stéphane Mounier; Cédric Garnier
      Pages: 133 - 145
      Abstract: Publication date: Available online 31 January 2018
      Source:Chemical Geology
      Author(s): Duc Huy Dang, R. Douglas Evans, Wei Wang, Dario Omanović, Amonda El Houssainy, Véronique Lenoble, Jean-Ulrich Mullot, Stéphane Mounier, Cédric Garnier
      By assessing U geochemistry as well as U isotopic composition in marine sediments of Toulon Bay, NW Mediterranean Sea, authigenic U accumulation was found to be tightly linked to that of Mo and V with slight differences in accumulation rate depending on sediment redox conditions. In sediments collected on a transect along a river plume, the authigenic accumulation of these redox-sensitive elements appears to be linked to sediment grain size which probably drives the redox status of the sediments. A typical U loss in re-oxidized sediments was observed in sediments that had been previously disturbed. However, the dissolved U profiles do not show a simple and typical depletion trend but rather a depletion in the top 10 cm followed by release in deeper pore waters that could be linked to a potential reoxidation/mobilization of authigenic U(IV). The released U could be further scavenged as a U-P precipitate. The U isotopic data (δ238U), which are the first reported for the coastal hypoxic sediments of Toulon Bay, average −0.12 ± 0.12‰ in surface sediments. However, sediments situated in front of river mouths show higher values of δ238U (up to +0.75‰); these high values are reported for the first time in sediments below an oxic water column.

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.01.032
      Issue No: Vol. 481 (2018)
  • Isotope-dilution anchoring of zircon reference materials for accurate
           Ti-in-zircon thermometry
    • Authors: Dawid Szymanowski; Manuela A. Fehr; Marcel Guillong; Matthew A. Coble; Jörn-Frederik Wotzlaw; Lutz Nasdala; Ben S. Ellis; Olivier Bachmann; Maria Schönbächler
      Pages: 146 - 154
      Abstract: Publication date: Available online 2 February 2018
      Source:Chemical Geology
      Author(s): Dawid Szymanowski, Manuela A. Fehr, Marcel Guillong, Matthew A. Coble, Jörn-Frederik Wotzlaw, Lutz Nasdala, Ben S. Ellis, Olivier Bachmann, Maria Schönbächler
      The temperature-dependence of Ti incorporation into zircon can be used to estimate crystallisation conditions and to make inferences about the petrogenesis of host rocks or parental melts. However, the foundation for such temperature estimates – Ti concentration in zircon – is currently determined by a variety of techniques with no common reference. Analyses of Ti in zircon commonly utilise in situ microbeam techniques such as secondary ion mass spectrometry (SIMS), laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS), and electron probe microanalysis (EPMA). These techniques require external calibrations that are prone to matrix effects, potentially imposing significant errors on Ti concentrations and the derived model temperatures. To improve the accuracy of these determinations, we present a new framework of zircon reference materials for Ti built around two thoroughly characterised zircons, the widely distributed zircon 91500 and the new reference zircon GZ7. Laser ablation ICP-MS and SIMS analyses reveal that the homogeneity with respect to Ti/Si is on the order of 4.1–8.2% (relative standard deviation, RSD) for zircon 91500 and 1.1% for zircon GZ7, which is considered sufficient for their use as primary calibration materials. We present independent determinations of Ti concentration in multiple fragments of these two zircon crystals using isotope dilution (ID)-ICP-MS employing a precisely calibrated 47Ti–49Ti double spike. The recommended ID Ti concentration values are 4.73 ± 0.15 μg g−1 for zircon 91500 and 25.08 ± 0.18 μg g−1 for zircon GZ7 (95% confidence level). A set of complementary secondary reference materials is also characterised using LA-ICP-MS with Ti concentrations anchored to the new isotope dilution values, thereby permitting comparisons of Ti-in-zircon datasets whenever data for these secondary reference materials are reported.

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.02.001
      Issue No: Vol. 481 (2018)
  • Variations of stable isotope fractionation during bacterial chromium
           reduction processes and their implications
    • Authors: Qiong Zhang; Ken Amor; Stephen J.G. Galer; Ian Thompson; Don Porcelli
      Pages: 155 - 164
      Abstract: Publication date: 20 March 2018
      Source:Chemical Geology, Volume 481
      Author(s): Qiong Zhang, Ken Amor, Stephen J.G. Galer, Ian Thompson, Don Porcelli
      Many chemical processes generate subtle but readily measured changes in isotope compositions of elements across the periodic table. The elements involved therefore carry diagnostic information about their chemical histories in complex geochemical or biochemical environments. Distinctive Cr isotope signatures can be used to identify immobilization processes of Cr in the environment, such as microbial Cr(VI) reduction, abiotic Cr(VI) reduction, and adsorption. Here we demonstrate that under well-controlled conditions, Cr isotopes can also be used to distinguish between different biological Cr(VI) reduction pathways. The reduction of Cr(VI) by two facultative anaerobic bacteria, Pseudomonas fluorescens LB 300 and Shewanella oneidensis MR 1, was investigated to determine the conditions under which Cr(VI) is reduced and to quantify the corresponding isotope signatures. The present study considers the effects of a broad range of parameters on Cr isotope fractionation, including bacterial species, electron donors, pH, and respiration pathways (aerobic vs. anaerobic) that must be considered for understanding Cr isotope variations under different experimental and environmental conditions. In the bacterial Cr(VI) reduction experiments, the 53Cr/52Cr isotope ratio of the remaining Cr(VI) increased by up to + 8‰, indicating that lighter isotopes of Cr were preferentially reduced. In aerobic experiments, although Cr reduction rates increased as pH increased from 4 to 8, the fractionation factor did not vary significantly (ε = −3.21 ± 0.18‰). Experiments using different electron donors demonstrated that citrate promoted the greatest Cr reduction rate compared with glucose, acetate, and propionate. Under aerobic conditions, although the Cr(VI) reduction rates varied substantially between different experimental settings, the isotope fractionation factors were indistinguishable between all the environmental conditions examined (ε = −3.1‰), with the exception of when citrate was the electron donor (ε = −4.3‰). Cr reduction rates were generally much faster under anaerobic conditions for both bacteria investigated. The utilisation of different electron donors resulted in the same Cr reduction rates by the bacteria, but fractionated Cr with a broad range of isotope fractionation factors, from − 1.58 ± 0.16‰ to − 4.93 ± 0.36‰. Although it has been proposed in many previous studies that there is an inverse relationship between reduction rates and the fractionation factors, no clear relationship between the reduction rates and fractionation factors was observed in this study. The Cr isotope fractionation factors ε were insensitive to pH and electron donor concentration, but dependent on the type of electron donors and redox conditions in the cultures. This indicates that isotope variations may be used to identify when different biological pathways are involved, and so to investigate metabolic processes. The ε value from all experimental conditions examined ranged between − 1.58 and − 4.93‰, with a mean value at − 3.3‰. While Cr isotopes might be used to separate the effects of abiotic and microbially mediated reduction in environmental sites, the fractionation factors from reduction by individual bacterial species overlap with those from several individual abiotic reduction processes, suggesting that site-specific data (e.g., fractionation factors associated with indigenous bacterial populations and local groundwater chemistry) are required in order to use Cr isotopes to distinguish between different reduction mechanisms.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.004
      Issue No: Vol. 481 (2018)
  • Corrigendum to “Characterization of helium release from apatite by
           continuous ramped heating” [CHEMGE: 476, 5 January 2018; 223-232]
    • Authors: Bruce D. Idleman; Peter K. Zeitler; Kalin T. McDannell
      First page: 165
      Abstract: Publication date: 20 March 2018
      Source:Chemical Geology, Volume 481
      Author(s): Bruce D. Idleman, Peter K. Zeitler, Kalin T. McDannell

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.006
      Issue No: Vol. 481 (2018)
  • Improved in situ Sr isotopic analysis by a 257nm femtosecond laser in
           combination with the addition of nitrogen for geological minerals
    • Authors: Wen Zhang; Zhaochu Hu; Yongsheng Liu; Tao Wu; Xiaodong Deng; Jingliang Guo; Han Zhao
      Pages: 10 - 21
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Wen Zhang, Zhaochu Hu, Yongsheng Liu, Tao Wu, Xiaodong Deng, Jingliang Guo, Han Zhao
      In situ Sr isotope analysis of geological materials by laser ablation multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is a powerful tracer technique for tracking magmatic source components and geological processes. However, the accuracy and precision of the 87Sr/86Sr ratio are limited in the analysis of natural minerals because of the low-Sr concentration, the isobaric interference or small grains with complex textural contexts, especially for transparent minerals such as feldspars. In this study, analytical results demonstrated that ablation rates in fs laser ablation were consistent for various samples (0.08–0.11μm per pulse), but those in ns laser ablation were obviously material properties-dependent, such as the rates of 0.026μm per pulse and 0.144μm per pulse for feldspar and pyrite, respectively. In addition, at similar energy fluences, the sensitivities of Sr in feldspars analyzed by the fs laser were 3.4 times higher than those analyzed by the ns laser due to the higher ablation efficiency of the fs pulse. These advantages of the fs laser not only offer the benefit of eliminating or weakening the matrix effect during the laser ablation processes but also help to improve the analytical precision for transparent minerals. We also demonstrated that the isobaric interferences of calcium dimers and argides (CaAr++CaCa+) and Kr+ were dramatically reduced by factors of 6.5–11.7 and 5–12.5 in the presence of 6–12mlmin−1 N2, respectively. Furthermore, with the addition of N2 (12mlmin−1), the sensitivity of Rb was inhibited, resulting in a decrease of 1.47 times in Rb/Sr signal ratios. Due to the effect of suppressing interferences by adding N2, both the stability and accuracy of the 87Sr/86Sr and 84Sr/86Sr ratios show improvement, especially for the Rb-rich feldspars. Combining the advantages of the fs laser system with the addition of nitrogen, an improved in situ Sr isotope analytical method is then developed. The satisfactory accuracy and precision of the 87Sr/86Sr ratio from natural plagioclases, a K-feldspar with high Rb/Sr ratios (0.46) and a low-Sr clinopyroxene were obtained, demonstrating the reliability of the proposed method. Four feldspars, which have different contents of the major elements, Sr and Rb, showed homogeneous Sr isotope compositions and were recommended as potential suitable reference materials for in situ Sr isotope analysis. As an application, two plagioclases in mafic microgranular enclaves (MMEs) with small grain sizes (200–300μm) and wide ranges of Rb/Sr ratios were analyzed and showed obvious variations of the 87Sr/86Sr ratios from core to rim, which indicated that the proposed method in this study can provide high spatial resolution geochemical information for a single mineral.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2017.12.018
      Issue No: Vol. 479 (2018)
  • A universal adsorption behaviour for Cu uptake by iron (hydr)oxide
           organo-mineral composites
    • Authors: Alba Otero Fariña; Caroline L. Peacock; Sarah Fiol; Juan Antelo; Benjamin Carvin
      Pages: 22 - 35
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Alba Otero Fariña, Caroline L. Peacock, Sarah Fiol, Juan Antelo, Benjamin Carvin
      Organo-mineral composites formed by the association of iron (hydr)oxides and organic matter are widespread in natural environments and play an important role as scavengers of bioessential elements and contaminants. To better understand the mobility and fate of Cu in natural soils and sediments we precipitated ferrihydrite and goethite organo-mineral composites using humic acid as an analogue for natural organic matter, with organic carbon content in the composites ranging from 2 to 16wt% C. We then measured the adsorption of Cu to the end-member mineral and organic phases and the composites as a function of pH and Cu concentration. We determined the molecular mechanisms of Cu adsorption to the end-member phases and the composites, and used this information to develop molecularly constrained thermodynamic surface complexation models to quantify Cu adsorption. By combining our work here with previous work on the adsorption of Cu to ferrihydrite-bacteria composites, we provide insight into the predominance of Cu-carboxyl binding for Cu adsorption to iron (hydr)oxide organo-mineral composites, and the nature of Cu adsorption behaviour across a range of iron (hydr)oxide composites composed of different minerals and different types of organic matter. Taken as a whole our results show that Cu adsorption to the carboxyl group present in organic matter coatings on iron (hydr)oxides is likely common to most iron (hydr)oxide composites, such that Cu-carboxyl binding provides a key control on the fate and mobility of Cu in soils and sediments. Our work also suggests there is a universal adsorption behaviour for Cu adsorption to ferrihydrite organo-mineral composites, in which the mineral:organic mass ratio is a crucial parameter for determining Cu uptake. Overall we show that ferrihydrite composites composed of different types of organic matter and containing a wide range of organic mass ratios, but where the mineral is the dominant composite fraction, possess additive Cu adsorption behaviour which can be predicted using a component additivity surface complexation model.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2017.12.022
      Issue No: Vol. 479 (2018)
  • Complexation of heavy metal cations on clay edges at elevated temperatures
    • Authors: Chi Zhang; Xiandong Liu; Xiancai Lu; Mengjia He
      Pages: 36 - 46
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Chi Zhang, Xiandong Liu, Xiancai Lu, Mengjia He
      Aiming at the complexation mechanism of heavy metals on clay edges at elevated temperatures, we carried out systematic first principles molecular dynamics (FPMD) simulations at 423K by taking Cd(II) and Ni(II) as model cations. The results show that stable surface complexes include monodentate complexes on ≡SiO site, bidentate complexes on ≡Al(OH)2 site, and tetradentate complexes on octahedral vacancy on (010) edges and monodentate complexes on ≡SiO site, bidentate complexes on ≡AlOH≡AlSiO site, and tetradentate complexes on vacancy on (110) edges. Constrained FPMD simulations were conducted to calculate the desorption free energies of the complexes of the two cations on (010) surface. The results show that the octahedral vacancy has significantly higher free energy than the other sites regardless of the coordination of Al(III), indicating that the vacancy is the most favorable complexing site at elevated temperatures. The same conclusion has been deduced for (110) edges. Computed pKa values show that only the complexes on vacancy sites can hydrolyze in the common pH range, whereas those on the other sites hardly dissociate due to the extremely high pKa values, that is, the former complexes can serve as complexing sites for more metal cations. Additional simulations show that multinuclear complexes of Cd(II) and Ni(II) hold stably at 423K, which may act as precursors for epitaxial growth of new mineral phases. This study forms a physical basis for understanding the behaviors of heavy metals in various environments of elevated temperatures, and provides fundamental data for further experimental and modelling studies.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2017.12.027
      Issue No: Vol. 479 (2018)
  • Reduction of structural Fe(III) in nontronite by thermophilic microbial
           consortia enriched from hot springs in Tengchong, Yunnan Province, China
    • Authors: Liuqin Huang; Can Feng; Hongchen Jiang; Hailiang Dong; Zizhang Liu; Qiang Zeng; Xi Wang; Li Zhang
      Pages: 47 - 57
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Liuqin Huang, Can Feng, Hongchen Jiang, Hailiang Dong, Zizhang Liu, Qiang Zeng, Xi Wang, Li Zhang
      Iron redox cycling provides one of the most important energy sources supporting microorganisms in terrestrial hot springs. In order to understand microbial Fe(III) reduction processes in hot springs, Fe(III)-reducing bacterial consortia were successfully retrieved from seven acidic hot springs in Tengchong County, Yunnan Province, China (a temperature range from 40.6°C to 74.7°C and a pH range from 2.64 to 4.72). These Fe(III)-reducing consortia were mainly composed of sulfate reducing bacteria (SRB, including Desulfotomaculum, Thermodesulfobacterium and Desulfomicrobium) and organic matter fermenting bacteria (Thermoanaerobacterium and Thermoanaerobacter), with each consortia having specific composition depending on the physio-chemical conditions of the studied hot springs. The obtained consortia were capable of dissimilatory reduction of Fe(III) in nontronite NAu-2 (ferruginous smectite) with 20.8% to 29.8% reduction extent and initial reduction rate of 0.011–0.023mMFe(III)/gNAu-2/h. These extents and rates were comparable to those by mesophilic Fe-reducers in the presence of electron shuttles. Both high temperature and the possible presence of electron-shuttles in hot springs may have accounted for these observed high reduction extents and rates. Various secondary minerals formed during NAu-2 bioreduction, including Fe sulfides and oxides, silicates, and silica. In one spring, illitization and kaolinization of smectite were observed, suggesting that Fe-reducers play important roles in mineral transformation in geothermal environments.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2017.12.028
      Issue No: Vol. 479 (2018)
  • Tracing metal sources in peribatholitic hydrothermal W deposits based on
           the chemical composition of wolframite: The example of the Variscan French
           Massif Central
    • Authors: Matthieu Harlaux; Julien Mercadier; Christian Marignac; Chantal Peiffert; Christophe Cloquet; Michel Cuney
      Pages: 58 - 85
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Matthieu Harlaux, Julien Mercadier, Christian Marignac, Chantal Peiffert, Christophe Cloquet, Michel Cuney
      We present a complete dataset for major, minor and trace elements in wolframite ([Fe,Mn]WO4) based on the example of several peribatholitic hydrothermal W deposits located in the Variscan French Massif Central (FMC). The wolframite samples were characterized down to the micrometer scale by combining scanning electron microscopy observations and in situ chemical analysis by electron probe microanalyzer and laser ablation – inductively coupled plasma – mass spectrometry. Most samples are Fe-dominated wolframites and are characterized by variable Fe/(Fe+Mn) values for the studied deposits (from 0.36 to 0.86) without significant alteration features. Wolframites present intracrystalline variations for concentrations of several minor and trace elements, principally for Nb, Ta, and Sn, which reflect growth zoning. The minor and trace element compositions of the different wolframite samples show at first order similar enrichments in Ta, Nb, Sn, Zn, and In, as well as depletions in LREE, Li, Th, Ti, Zr, Hf, Pb, V, Co, and Mg, compared to the upper continental crust. Second order compositional variations are observed between the studied deposits, which can be separated in four main regional geochemical groups. This work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary hydrothermal fluid. The regional variations observed in the geochemical signatures of wolframite reflect local variations in the composition of the hydrothermal fluid, i.e. variable metal sources. Therefore, this suggests that the minor and trace element contents in wolframite likely represent direct markers of the source of the hydrothermal fluid and ultimately of the metals. The comparison between the trace element compositions of wolframite with the compositions of regional granitic rocks and worldwide shales suggests that evolved peraluminous granites represent the main source of metals in peribatholitic hydrothermal W deposits from the FMC, whereas metasedimentary rocks have a limited to no influence on the metal budget.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2017.12.029
      Issue No: Vol. 479 (2018)
  • Mercury stable isotope compositions in magmatic-affected coal deposits:
           New insights to mercury sources, migration and enrichment
    • Authors: Liugen Zheng; Ruoyu Sun; Holger Hintelmann; Jianming Zhu; Ruwei Wang; Jeroen E. Sonke
      Pages: 86 - 101
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Liugen Zheng, Ruoyu Sun, Holger Hintelmann, Jianming Zhu, Ruwei Wang, Jeroen E. Sonke
      Mercury (Hg) is commonly present at trace levels in coal deposits. Geological processes, particularly magmatic intrusion and hydrothermal cycling in coal-bearing strata can significantly increase Hg levels in coals. However, the effects of thermal stress, magmatic components, magmatic-hydrothermal fluids, low-temperature hydrothermal fluids on Hg enrichment are confounded in a magmatic-affected coal basin. Here, we demonstrate the use of stable Hg isotopes to understand the controlling factors on Hg enrichment in two well-known Chinese coal deposits affected by magmatic activities: Wulantuga low-temperature hydrothermal-altered coal deposit and Wolonghu magmatic-intruded coal deposit. The Wulantuga No. 6 coal seam is extremely enriched in Hg, varying from 0.37μg/g in middle coal benches to 40–90μg/g in the upper most and lowest coal benches. Approximately 2.5‰ variation in mass dependent fractionation (MDF, −3.07‰ to −0.58‰ in δ202Hg) is observed. δ202Hg vs. 1/[Hg] diagram suggests a mixture of three Hg end-members: original hydrothermal fluids, fractionated hydrothermal fluids and native coal-forming materials. In addition, Wulantuga coals all show positive mass independent fractionation (MIF) of odd isotopes, up to 0.87‰ in Δ199Hg and 0.66‰ in Δ201Hg. The Δ199Hg/Δ201Hg ratios range from 1.3 to 3.3, suggesting that a large fraction of photodegraded methylmercury was likely incorporated into the coal deposit. The magmatic-intruded Wolonghu No. 8 coal seam is only slightly to intermediately enriched in Hg, varying from 0.10μg/g to 0.40μg/g. The coals near the contact sill (≤5cm, −1.81‰ to −1.52‰) have similar δ202Hg as the magmatic sill rocks (−2.05‰ to −1.80‰), both with insignificant MIF values. Coals far from the contact sill (≥15cm) have δ202Hg values varying from −3.40‰ to −1.61‰ and Δ199Hg varying from 0.26‰ to 0.58‰, which are significantly enriched in light and odd Hg isotopes compared to coals near the contact sill. Δ199Hg and Δ201Hg in Wolonghu coals far from the contact sill resemble those of meteoritic waters and seawater in both magnitude and Δ199Hg/Δ201Hg ratio. Our two case studies show significant MDF and MIF of Hg isotopes, which inform on Hg migration and sequestration in the magmatic rocks and coal deposits, and on the roles of meteoric water and hydrothermal fluid circulation.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2017.12.032
      Issue No: Vol. 479 (2018)
  • Sr–Nd isotopic geochemistry of Holocene sediments from the South Yellow
           Sea: Implications for provenance and monsoon variability
    • Authors: Bangqi Hu; Jun Li; Jingtao Zhao; Hong Yan; Liang Zou; Fenglong Bai; Fangjian Xu; Xuebo Yin; Gangjian Wei
      Pages: 102 - 112
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Bangqi Hu, Jun Li, Jingtao Zhao, Hong Yan, Liang Zou, Fenglong Bai, Fangjian Xu, Xuebo Yin, Gangjian Wei
      Elemental geochemical and Sr–Nd isotopic signatures are used to decipher terrigenous sediments provenances and transport mechanisms in the South Yellow Sea during the Holocene. 87Sr/86Sr ratios in the Chinese and Korean riverine sediments overlap each other, whereas εNd values of Korean riverine sediments are generally less radiogenic in comparison to the Changjiang and Huanghe. Moreover, εNd values of these two large rivers appear unaffected by mineral sorting and are relative stable during the Holocene. We propose a three endmembers (i.e., the Changjiang, the Huanghe, and Korean rivers) mixing model to explain sediment provenances in the Central Yellow Sea Mud (CYSM). Mixing calculations show that the Huanghe is the major sediment contributor to the CYSM before ~8ka (thousand years before 1950CE), whereas the Changjiang has become the predominant sediment source after ~8ka. Holocene changes in riverine sediment supplies to the CYSM are closely related to the oceanic circulation, monsoon climate, and drainage changes. After examining several hypotheses to explain the variations in 87Sr/86Sr ratios of Core YSC-1 during the past ~8kyr, we tentatively attribute that to changes in the erosion patterns of the Changjiang Basin. This in turn is associated with the asynchronous evolution of monsoon precipitation in the upper (Indian Summer Monsoon) and middle-lower Changjiang (East Asian Summer Monsoon). Therefore, our results highlight significant influences of monsoon climate on erosion patterns within the Changjiang catchment at millennial timescales.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2017.12.033
      Issue No: Vol. 479 (2018)
  • Evaluating baddeleyite oxygen isotope analysis by secondary ion mass
           spectrometry (SIMS)
    • Authors: J.H.F.L. Davies; R.A. Stern; L.M. Heaman; D.E. Moser; E.L. Walton; T. Vennemann
      Pages: 113 - 122
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): J.H.F.L. Davies, R.A. Stern, L.M. Heaman, D.E. Moser, E.L. Walton, T. Vennemann
      Two baddeleyite megacrysts were evaluated as potential reference materials (RMs) for SIMS oxygen isotope analysis, and utilized to understand and calibrate instrumental mass fractionation (IMF). A baddeleyite crystal (S0045) from the Phalaborwa carbonatite, South Africa has a mean δ18OVSMOW = +4.6 ± 0.3‰ (range 0.75‰) measured using laser fluorination gas source mass spectrometry (LF-GMS) and one (S0069) from the Mogok metamorphic belt, Myanmar has δ18OVSMOW = +22.2 ± 0.4‰ (range 0.89‰). SIMS standardization utilizing these inherently heterogeneous RMs is possible by analyzing a number of crystal fragments and utilizing one of them lying at the median of the range. Metamictization, lattice orientation, and chemical composition do not appear to be significant (<0.5‰) variables in matrix matching of RMs and unknowns. Propagation of errors while utilizing the imperfect RMs results in 10 μm diameter spot uncertainties of about ±0.3‰ (2σ). SIMS oxygen isotope analysis of co-crystalline zircon and baddeleyite from the 2.2 Ga Duck Lake sill (DLS) in the Northwest Territories, Canada, yield predominant δ18OVSMOW modes of +6.0‰ and +3.2‰, respectively. This difference is consistent with preserving high-temperature isotopic equilibrium between zircon and baddeleyite. DLS baddeleyite δ18O data as a whole are negatively skewed (to 0.0‰), and interpreted to reflect low temperature, open-system behaviour. Zircon δ18O are less affected, but also show hints of the same influences of secondary alteration and oxygen isotope exchange.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.002
      Issue No: Vol. 479 (2018)
  • Sample preparation for determination of comminution ages in lacustrine and
           marine sediments
    • Authors: Alexander Francke; Sally Carney; Patrick Wilcox; Anthony Dosseto
      Pages: 123 - 135
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Alexander Francke, Sally Carney, Patrick Wilcox, Anthony Dosseto
      The uranium isotope composition (234U and 238U) of detrital matter has become an essential tool for evaluating the response of erosion and catchment dynamics to climate variability on geological time scales. Relative variability of the (234U/238U) activity ratio can be used as an estimate of the time that has elapsed since physical and chemical weathering has formed grains <63μm, termed comminution age, as a result of ongoing depletion of 234U in detrital matter. However, as non-detrital (authigenic, endogenic) components are commonly enriched in 234U, sequential extraction methods are required to carefully remove any non-detrital matter from the sediments. Herein, we tested different methods, which use similar chemical reactants but differ in terms of applied heat and time. Based on the results, it can be inferred that an ultrasound-assisted approach enables the removal of non-detrital matter from the sediments without alternating the isotope ratio of the detrital grain, and provides a high reproducibility of the (234U/238U) activity ratios. Moreover, it is the fastest, and thus, most cost effective method tested. Fast and cost-effective treatment methods are a prerequisite for high-resolution studies on long paleoenvironmental records, and thus, these results are fundamental for the further development of U isotope analyses as a tool for the reconstruction of past erosion and catchment dynamics in response to climate variability. Combined U isotopes and gas absorption surface area analyses on two sediment samples from the Mediterranean Sea yield comminution ages up to 5 times older after sample treatment, which highlights the importance of a comprehensive removal of non-detrital matter from the bulk sediment composition. Moreover, gas sorption analysis allowed determining whether a fractal correction for calculation of the recoil fraction should be applied. Precise estimates of the recoil fraction are crucial for calculating the comminution ages, as it governs the loss of 234U from detrital matter. Samples analyzed in this study display Type II isotherms suggesting a non-porous or macroporous surface. Micro- and mesopores, which increase the surface area during gas absorption analyses but do not contribute to the loss of 234U are absent. Thus, a fractal correction to account for micro- and mesopores is not required.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.003
      Issue No: Vol. 479 (2018)
  • Combined dating of goethites and kaolinites from ferruginous duricrusts.
           Deciphering the Late Neogene erosion history of Central Amazonia
    • Authors: Thierry Allard; Cécile Gautheron; Silvana Bressan Riffel; Etienne Balan; Bruna Fernandes Soares; Rosella Pinna-Jamme; Alexis Derycke; Guillaume Morin; Guilherme Taitson Bueno; Nadia do Nascimento
      Pages: 136 - 150
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Thierry Allard, Cécile Gautheron, Silvana Bressan Riffel, Etienne Balan, Bruna Fernandes Soares, Rosella Pinna-Jamme, Alexis Derycke, Guillaume Morin, Guilherme Taitson Bueno, Nadia do Nascimento
      This study focuses on the dating of millimetric pisoliths from ferruginous duricrusts located in central Amazonia (Brazil), by coupling detailed mineralogy and two relevant dating methods: (i) (U-Th)/He analysis of goethites by mass spectrometry; (ii) analysis of radiation-induced defects of kaolinites embedded in duricrusts by electron paramagnetic resonance spectroscopy (EPR). Three samples collected at different elevations in the landscape were selected. The goethite corrected ages range from 1.1–15.2 Ma and consistently increase with elevation. EPR was performed on kaolinites after several cycles of a deferration procedure. Considering extreme geochemical scenarii, the ages of kaolinites are 1.7–7.1 Ma for a closed system and 4.0–16.7 Ma for an open system with 100% Rn loss. Ages of goethites and kaolinites are close, in the limit of the uncertainty of the methods. They show important periods of duricrust formation at Middle Miocene and at Late Miocene/Pliocene. Data allow the estimation of lowering rates between 3 and 8 m/Ma, in agreement with independent data available in the literature for the central Amazonia region or even for erosion of other cratons in the world. The two dating methods can be compared on common duricrust samples. By revealing single or multi-step weathering/erosion episodes related to relictual paleosurfaces, they also bring promising contributions to an advanced knowledge of ancient and complex lateritic geosystems.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.004
      Issue No: Vol. 479 (2018)
  • Carbonate speciation in depolymerized and polymerized (alumino)silicate
           glasses: Constraints from 13C MAS and static NMR measurements and ab
           initio calculations
    • Authors: Xianyu Xue; Masami Kanzaki; Paul Floury; Tsubasa Tobase; James Eguchi
      Pages: 151 - 165
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Xianyu Xue, Masami Kanzaki, Paul Floury, Tsubasa Tobase, James Eguchi
      Knowledge of the dissolution mechanisms of carbon dioxide in silicate melts/glasses is indispensable for understanding its effects on physical and thermodynamic properties. Carbon dioxide is generally known to dissolve as molecular CO2 and CO3 2– species, with the latter dominant for depolymerized compositions. However, less is agreed upon about how the CO3 2– groups are incorporated, especially for depolymerized silicate melt compositions relevant to natural mafic and ultramafic magmas. Here we report 13C MAS and static NMR results on a series of 13CO2-bearing glasses (quenched from melts) of diverse silicate compositions, including nominally fully polymerized sodium aluminosilicate and calcium aluminosilicate, depolymerized sodium silicate and sodium aluminosilicate, and depolymerized calcium‑magnesium silicate and calcium aluminosilicate compositions (with varying degrees of polymerization), as well as ab initio calculations, to provide new constraints on the speciation of carbonates in silicate melts/glasses as a function of composition. The ab initio calculation revealed that both vibrational frequencies and 13C chemical shift tensor are sensitive to the local environments of carbonates. The splittings of the asymmetric stretching doublets (Δν3) for CO3 2– groups bonded to one or two tetrahedral Si/Al via two oxygens (network carbonates) are all relatively large (around 180–480 cm−1), contrary to previous speculations. In comparison, experimental data for CO3 2– groups bonded only to metal cations (free carbonates) in minerals show zero to moderate Δν3 (up to ~100 cm−1). Our calculations also showed that network carbonates bonded to one or two tetrahedral Si/Al both show 13C chemical shift tensor parameters (especially skew and isotropic chemical shift) that are distinctly different from those of free carbonates. Our 13C MAS and static NMR data, as well as infrared spectroscopic data (moderate Δν3 of 60–100 cm−1) from the literature, for depolymerized silicate and aluminosilicate glasses are all indicative of free carbonates as the dominant species. Data for nominally fully polymerized aluminosilicate compositions, on the other hand, are consistent with carbonate groups bonded to two Si/Al via two oxygens (network carbonate) as the dominant species. The quantitative 13C MAS NMR data also revealed the coexistence of a small amount of the other type of carbonate species, especially for Ca aluminosilicate glasses. These new structural insights should be valuable in helping better understand physical properties (e.g. viscosity) of CO2-bearing silicate melts of diverse compositions.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.005
      Issue No: Vol. 479 (2018)
  • Bulk solubility and speciation of H2O in silicate melts
    • Authors: G. Ottonello; P. Richet; P. Papale
      Pages: 176 - 187
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): G. Ottonello, P. Richet, P. Papale
      The bulk solubility and speciation of H2O in silicate melts of virtually any composition is predicted from first principles with a satisfactory precision. The solubility of molecular water is first predicted from the Scaling Particle Theory (SPT) coupled with an ab initio assessment of the electronic, dispersive and repulsive energy terms based on the Polarized Continuum Model (PCM). The Silver-Stolper ideal homogeneous speciation model is then applied to compute the fractional molar amount of neutral hydroxyl functionals [OH]0 in the melt and the computed [OH]0 amount is added to the molecular form [OH2]. The Hydrogen Bonding (HB) electrostatic contributions to the stabilization of molecular water [OH2] in solution are then resolved through an inverse non-linear minimization procedure on the basis of an extended dataset (970 samples) of experiments concerning the H2O saturation hyper-surface carried out in the last half century. The Gibbs free energy of solution ΔGS, the ΔGHB contributions and the energy terms involved in the homogeneous speciation reaction are shown to be consistent with first principles. The procedure is fully predictive (i.e. no need of an initial hint about approximate bulk amounts of H2O in solution) and sufficiently accurate to be proposed as an exploratory tool (mean absolute accuracy of ~2.1 kJ/mol in terms of energy and ~1.7% in terms of fractional molar amount XH2O per unit mole of liquid).

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.008
      Issue No: Vol. 479 (2018)
  • Distribution of Rb, Ga and Cs in agricultural land soils at European
           continental scale (GEMAS): Implications for weathering conditions and
    • Authors: Philippe Négrel; Anna Ladenberger; Clemens Reimann; Manfred Birke; Martiya Sadeghi
      Pages: 188 - 203
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Philippe Négrel, Anna Ladenberger, Clemens Reimann, Manfred Birke, Martiya Sadeghi
      Agricultural soil (Ap-horizon, 0–20 cm) samples were collected from a large part of Europe (33 countries, 5.6 million km2) as part of the GEMAS (GEochemical Mapping of Agricultural and grazing land Soil) soil mapping project. The soil data have been used to provide a general view of element mobility and source rocks at the continental scale, either by reference to average crustal abundances or to normalised patterns of element mobility during weathering processes. The survey area includes a diverse group of soil parent materials with varying geological history, a wide range of climate zones, and landscapes. Total concentrations of Rb, Ga, and Cs in European soil were determined by XRF (X-ray fluorescence spectrometry). In addition, hot aqua regia available element concentrations were analysed by inductively coupled plasma-mass spectrometry ICP-MS. Their spatial distribution patterns are shown in geochemical maps. The spatial distribution of Rb, Ga and Cs in Ap soil is quite comparable for the aqua regia and XRF results. The Cs spatial pattern reflects best the large difference between trace element concentrations in northern Europe with predominantly low concentrations and southern Europe with approximately two times higher values. The maximum extent of the last glaciation is visible as a clear concentration break on the map. Lithology of the underlying bedrock is inferred as the major source of geochemical anomalies. In search for characterising the soil parent material and degree of weathering, the soil data were examined for Ga and Cs using two methods. First, the estimated degree of extractability DEi of an element in a sample was calculated by dividing aqua regia available concentrations by the total concentrations obtained by XRF analysis for Al, Na, Ca, K, Rb, Ga and Cs. The different DEi were investigated for 10 geological parent material subgroups (alkaline rocks, granite, calcareous rocks, basalt-mafic rocks, unclassified lithologies, Precambrian granitic gneiss bedrocks, loess, organic soils, schist and soil developed on coarse-grained sandy deposits). The role of clay as main carrier of Ga and Cs phases was inferred for soils developed on several types of bedrock such as granite, gneiss and alkaline rocks. Additionally, an affinity of Cs for loess and carbonate rocks has been observed.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.009
      Issue No: Vol. 479 (2018)
  • Transport of rare earth elements by hydrocarbon-bearing brines:
           Implications for ore deposition and the use of REEs as fluid source
    • Authors: Pilar Lecumberri-Sanchez; Mohammed Bouabdellah; Oussama Zemri
      Pages: 204 - 215
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Pilar Lecumberri-Sanchez, Mohammed Bouabdellah, Oussama Zemri
      Low-temperature (100–160 °C) hydrocarbon-bearing brines mobilize REE at concentrations up to several thousand ppm total rare earth elements (ΣREE) at El Hammam, Morocco. The major element chemistry (Na, Ca, Mg) and temperature of the fluids in this system are consistent with those of oil field brines. In contrast, REE concentrations in the fluid suggest a significant element input from a magmatic source. Spatially related lamprophyres predating the formation of El Hammam share a similar trace element signature. Therefore, hydrocarbon-bearing basinal brines seem to have leached some of these elements through fluid–rock interaction from the lamprophyres, supporting the ability of oil-field brines to mobilize not only base metals (as in Mississippi Valley Type [MVT] deposits), but also rare earth elements. The stability constants of REE aqueous complex at temperatures of 100–160 °C, the chemistry of oil-field brines worldwide, and the partitioning behavior of REE between fluorite and water at El Hammam indicate that acetate (± carbonate and fluoride) are likely to be major contributors to REE mobilization in these settings. The direct implications of the low temperature transport of REE by oil-bearing brines is that, in systems where these kind of fluids occur, the REE signature observed may not reflect the source of the fluid as much as a combination of fluid source and fluid-rock interaction. In addition, oil-field brines can efficiently scavenge, transport, and deposit REE leading to anomalously high accumulations such as the El Hammam fluorite deposit and may also contribute to REE mobilization and concentration in other systems.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.010
      Issue No: Vol. 479 (2018)
  • The relationship between Mn oxidation state and structure in triclinic and
           hexagonal birnessites
    • Authors: Florence T. Ling; Jeffrey E. Post; Peter J. Heaney; Eugene S. Ilton
      Pages: 216 - 227
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Florence T. Ling, Jeffrey E. Post, Peter J. Heaney, Eugene S. Ilton
      Because of their nanocrystallinity and high cation exchange capacities, birnessite phases can control the cycling of heavy metals in soils and groundwaters, and they also are implicated in the oxidation of transition metals in natural environments. Birnessite reactivity is determined by crystal structure and composition. Because birnessites typically are poorly crystalline, synchrotron-based absorption spectroscopy (EXAFS, XANES) often is utilized for structural characterization. For example, linear combination fitting (LCF) of X-ray absorption spectra typically is applied to quantify mixed triclinic and hexagonal birnessite phases. This approach is challenged, however, because the structures of the standards are not always plainly apparent. Moreover, it is difficult to distinguish birnessites with nanoscale intergrowths of hexagonal and triclinic endmembers from homogeneous birnessite structures of “intermediate triclinicity”. We explored these issues by synthesizing a host of cation-exchanged birnessite specimens whose long-range symmetrical character could be determined by X-ray diffraction without ambiguity. Through a combination of Fourier transform infrared spectroscopy (FTIR), extended X-ray absorption fine structure (EXAFS), and X-ray photoelectron spectroscopy (XPS), we have examined the relationships among structural symmetry, Mn oxidation state, and interlayer composition. Our results confirm prior models that as the concentration of Mn3+ increases, the departure from hexagonal symmetry also increases. Rietveld refinements indicate that the Jahn-Teller distortions associated with Mn3+ induce systematic variations in unit-cell parameters, particularly an increase in the a-axis and the β angle of the unit cell. Interlayer cation composition also controls structural distortions, and Ca-rich birnessites showed less deviation from hexagonality than did Na-, K-, and Ba-birnessites. Our linear combination fits of X-ray absorption spectra sometimes yielded misleading results, reinforcing the difficulty and importance of selecting appropriate standards.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.011
      Issue No: Vol. 479 (2018)
  • Mantle sources of kimberlites through time: A U-Pb and Lu-Hf isotope study
           of zircon megacrysts from the Siberian diamond fields
    • Authors: Jing Sun; Sebastian Tappe; Sergey I. Kostrovitsky; Chuan-Zhou Liu; Sergey Yu. Skuzovatov; Fu-Yuan Wu
      Pages: 228 - 240
      Abstract: Publication date: 20 February 2018
      Source:Chemical Geology, Volume 479
      Author(s): Jing Sun, Sebastian Tappe, Sergey I. Kostrovitsky, Chuan-Zhou Liu, Sergey Yu. Skuzovatov, Fu-Yuan Wu
      A comprehensive, internally consistent U-Pb and Lu-Hf isotope data set for 93 mantle-derived zircons from the Yakutian kimberlite province confirms and further refines the four major episodes of kimberlite magmatism on the Siberian craton: 421–409 Ma (Late Silurian-Early Devonian), 358–353 Ma (Late Devonian-Early Carboniferous), 226–218 Ma (Late Triassic), and 161–144 Ma (Middle-Late Jurassic). The relatively narrow, constant range of εHf values between +2 and +10 for both the Paleozoic and Mesozoic mantle-derived zircons (and by inference kimberlites) suggests that the volatile-rich magmas were repeatedly sourced from the convecting upper mantle beneath the Siberian craton. This finding is in keeping with the narrow and constant range of εNd values for groundmass perovskites from the Yakutian kimberlite province between +1.8 and +5.5 between 420 and 150 Ma. Our preferred model implies that the convecting upper mantle beneath the Yakutian kimberlite province ‘recovered’ rapidly back to ambient conditions shortly after the giant plume-related flood volcanic event that produced the Siberian Traps at 250 Ma. Although close spatial relationships exist between kimberlites and flood basalts on the Siberian craton during both the Paleozoic and Mesozoic, exact timing of the igneous events and the isotopic compositions of the diverse deep-sourced melting products rule out any direct genetic links. Besides the highly economic kimberlite-hosted diamond deposits of Late Devonian age (e.g., Mir and Udachnaya), the Siberian craton also contains significant Mesozoic placer diamond deposits (e.g., along the Anabar river), for which lamproite sources have been suggested recently. Our study shows that mantle-derived zircon megacryst fragments from the Ebelyakh placer deposit have Late Triassic ages of ca. 224 Ma. Their long-term depleted Hf isotopic compositions (+8.5 εHf) suggest that the alluvial diamonds were sourced from asthenosphere-derived Triassic kimberlites rather than from lithospheric mantle derived isotopically enriched lamproites.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.01.013
      Issue No: Vol. 479 (2018)
  • The stable isotope fingerprint of chemosymbiosis in the shell organic
           matrix of seep-dwelling bivalves
    • Authors: Dong Feng; Jörn Peckmann; Niu Li; Steffen Kiel; Jian-Wen Qiu; Qianyong Liang; Robert S. Carney; Yongbo Peng; Jun Tao; Duofu Chen
      Pages: 241 - 250
      Abstract: Publication date: Available online 31 January 2018
      Source:Chemical Geology
      Author(s): Dong Feng, Jörn Peckmann, Niu Li, Steffen Kiel, Jian-Wen Qiu, Qianyong Liang, Robert S. Carney, Yongbo Peng, Jun Tao, Duofu Chen
      Chemosymbiotic bivalves harboring endosymbiotic, chemotrophic bacteria have been investigated from a variety of hydrocarbon seeps worldwide. It has been shown that carbon, nitrogen, and sulfur isotopic compositions of the animal soft body parts are excellent indicators for evaluating energy transfer and food sources for the respective deep-sea habitats. However, recognition of chemosymbiosis has proven to be difficult for bivalves that dwelled at ancient seeps due to the lack of soft tissue. Here, we investigated δ13C, δ15N, and δ34S signatures of the tissue (mantle) and the shell organic matrix (SOM) of the same specimens of three bathymodiolin mussel species with different chemotrophic symbionts (methanotrophs in Bathymodiolus platifrons and B. childressi and thiotrophs in B. aduloides) and one vesicomyid clam (Calyptogena sp.) from a variety of hydrocarbon seeps from the South China Sea and the Gulf of Mexico. The data obtained demonstrate that all seep bivalves regardless of species or locations reveal overall small differences in δ13C (≤+4‰), δ15N (≤+1‰), and δ34S (≤+5‰) values between SOM and mantle (∆SOM-mantle) of the specimens. Relatively larger ∆SOM-mantle for δ13C values (as high as +10‰) in B. platifrons and larger ∆SOM-mantle for δ34S values (up to 16‰) in B. aduloides and Calyptogena sp. might be due to different symbionts in their gills. Since SOM can be extracted from fossil bivalve shells, the proxy can be used as a fingerprint of chemosynthesis-based food chains, although its utility will depend on the quality of preservation of the shell organic matter. Despite this uncertainty, the new proxy has great potential to reconstruct energy flow through different types of chemosynthesis-based ecosystems.

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.01.015
      Issue No: Vol. 479 (2018)
  • Nanoscale distribution of Pb in monazite revealed by atom probe microscopy
    • Authors: D. Fougerouse; S.M. Reddy; D.W. Saxey; T.M. Erickson; C.L. Kirkland; W.D.A. Rickard; A.-M. Seydoux-Guillaume; C. Clark; I.S. Buick
      Pages: 251 - 258
      Abstract: Publication date: Available online 3 February 2018
      Source:Chemical Geology
      Author(s): D. Fougerouse, S.M. Reddy, D.W. Saxey, T.M. Erickson, C.L. Kirkland, W.D.A. Rickard, A.-M. Seydoux-Guillaume, C. Clark, I.S. Buick
      The widespread use of monazite (LREEPO4) in U-Pb geochronology is underpinned by the assumption that it incorporates negligible amounts of Pb during initial growth, and that radiogenic Pb remains immobile after formation. We have investigated the nanoscale distribution of Pb in monazite from granulite facies rocks of the Sandmata Metamorphic Complex (Rajasthan, India) by atom probe microscopy to further understand the utility of monazite as a geochronometer. The studied monazite contains distinct 10 nm clusters, enriched in Ca and with a bulk composition consistent with them being apatite (Ca5(PO4)3(OH)), that are also enriched in Si and Pb relative to the monazite host. The 208Pb/232Th ratios of the clusters ranged from 1.1 ± 0.1 to 1.4 ± 0.2 (2σ), indicating that the clusters hold unsupported Pb. The 208Pb/232Th ratios of the whole specimen (including clusters) and the matrix alone are similar (<6% difference), indicating that the clusters formed shortly after monazite crystallisation by a phase exsolution mechanism that partitioned the initial common Pb and the minor radiogenic Pb into apatite. A volume-dependent analysis of the bulk monazite composition shows that a large variability in the Ca and, by proxy, Pb composition at small volumes (125 to 10,000 nm3) due to its heterogeneous distribution in the clusters, may have detrimental effects on radiometric dating with small analytical volumes. At larger volumes, including those used in EPMA and traditional isotopic dating methods (LA-ICPMS, SIMS), the variability of Pb content is negligible. However, the measured composition may result from the mixing of multiple reservoirs.
      Graphical abstract image

      PubDate: 2018-02-05T05:54:51Z
      DOI: 10.1016/j.chemgeo.2018.01.020
      Issue No: Vol. 479 (2018)
  • Leaching behavior of selenium from the karst infillings of the
           hydrogeological experimental site of Poitiers
    • Authors: Joseph Bassil; Aude Naveau; Maïté Bueno; Moumtaz Razack; Véronique Kazpard
      Abstract: Publication date: Available online 24 February 2018
      Source:Chemical Geology
      Author(s): Joseph Bassil, Aude Naveau, Maïté Bueno, Moumtaz Razack, Véronique Kazpard
      The selenium enrichment in groundwater may be caused by the contact with sedimentary formations. In many French regions, geogenic sedimentary sources of Se were identified as responsible of the Se concentrations exceeding the European limit in many wells designated to produce drinking water. This study focuses on the black argillaceous infillings of the Hydrogeological Experimental Site of Poitiers (HESP) and aims to better understand the Se release mechanisms at the interface between these infillings and aqueous media using batch experiments with variable pH and contact time. The Se behavior as function of pH was similar in the ultrapure water and in the HESP water and can be discriminated in three main domains. For very acidic domain the speciation of the released Se, that can be associated to the dissolution of some mineral phases, was majorly unidentified. For 2 < pH < 7.5, Se is mainly released as oxyanions which can be associated to interfacial processes. For basic pH, the maximal quantity of Se was released as oxyanions and unidentified species and is accompanied with the Fe and organic carbon mobilization. The kinetic data showed that the HESP water enhance the Se mobilization as function of time. The kinetic release of Se can be modeled as the release of three main fractions that cannot be directly correlated to the Se speciation: an immediate fraction followed by the release of two fractions corresponding to the pseudo first order kinetic. These results coupled with some in-situ data confirm the diversity and the complexity of the release mechanisms of Se that is not associated with a specific carrier phase but disseminated within the sedimentary matrix.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.032
  • A cryogenic XPS study of Ce fixation on nanosized manganite and vernadite:
           Interfacial reactions and effects of fulvic acid complexation
    • Authors: Changxun Yu; Jean-François Boily; Andrey Shchukarev; Henrik Drake; Zhaoliang Song; K. Johan Hogmalm; Mats E. Åström
      Abstract: Publication date: Available online 23 February 2018
      Source:Chemical Geology
      Author(s): Changxun Yu, Jean-François Boily, Andrey Shchukarev, Henrik Drake, Zhaoliang Song, K. Johan Hogmalm, Mats E. Åström
      This study investigated interfacial reactions between aqueous Ce(III) and two synthetic nanosized Mn (hydr-)oxides (manganite: γ-MnOOH, and vernadite: δ-MnO2) in the absence and presence of Nordic Lake fulvic acid (NLFA) at circumneutral pH by batch experiments and cryogenic X-ray photoelectron spectroscopy (XPS). The surfaces of manganite and vernadite were negatively charged (XPS-derived loadings of (Na + K)/Cl > 1) and loaded with 0.42–4.33 Ce ions nm−2. Manganite stabilized Ce-oxidation states almost identical to those for vernadite (approximately 75% Ce(IV) and 25% Ce(III)), providing the first experimental evidence that also a Mn(III) phase (manganite) can act as an important scavenger for Ce(IV) and thus, contribute to the decoupling of Ce from its neighboring rare earth elements and the development of Ce anomaly. In contrast, when exposed to Ce(III)-NLFA complexes, the oxidation of Ce by these two Mn (hydr-)oxides was strongly suppressed, suggesting that the formation of Ce(III) complexes with fulvic acid can stabilize Ce(III) even in the presence of oxidative Mn-oxide surfaces. The experiments also showed that Ce(III) complexed with excess NLFA was nearly completely removed, pointing to a strong preferential sorption of Ce(III)-complexed NLFA over free NLFA. This finding suggests that the Ce(III)-NLFA complexes were most likely sorbed by their cation side, i.e. Ce(III) bridging between oxide groups on the Mn (hydr-)oxides and negatively-charged functional groups in NLFA. Hence, Ce(III) was in direct contact with the oxidative manganite and vernadite but despite that not oxidized. An implication is that in organic-rich environments there may be an absence of Ce(IV) and Ce anomaly despite otherwise favorable conditions for Ce(III) oxidation.
      Graphical abstract image

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.033
  • Large Ca stable isotopic (δ44/40Ca) variation in a hand-specimen sized
           spheroidally weathered diabase due to selective weathering of
           clinopyroxene and plagioclase
    • Authors: Anupam Banerjee; Ramananda Chakrabarti
      Abstract: Publication date: Available online 23 February 2018
      Source:Chemical Geology
      Author(s): Anupam Banerjee, Ramananda Chakrabarti
      Calcium stable isotopic compositions (δ44/40CaSRM 915a) as well as selected major and trace element concentrations are reported for micro-drilled samples of a hand-specimen sized spheroidally weathered diabase (synonymously used as dolerite or microgabbro) from southern India. A sample of the ~2.37 Ga old un-weathered diabase (UW) dike was also analyzed. X-ray micro-CT imaging of a representative portion of the weathered sample shows the presence of two dominant mineral phases, plagioclase and clinopyroxene, with minor proportions of an iron-bearing phase (possibly haematite or ilmenite). Two different generations of cross-cutting micro-fractures are identified from the micro-CT image. The older fracture is sealed with secondary mineral deposits. The δ44/40Ca values of the weathered samples range from 0.42‰ to 0.84‰ with samples showing both higher and lower values than that of the un-weathered diabase dike which shows a δ44/40Ca value of 0.65‰. The variation in δ44/40Ca in the weathered samples is significantly higher than the external reproducibility of our measurements (<0.1‰) based on multiple measurements of Ca isotopic standards SRM 915a, SRM 915b and seawater (NASS-6). Mass balance calculations based on Sr/Ca and δ44/40Ca values rule out the contributions of secondary silicates as well as carbonates in causing the variability of δ44/40Ca in the weathered samples. The positive correlations between δ44/40Ca and Mg/Al, Mg/Na in the weathered samples further negate the possible contribution of secondary carbonates in causing the variability in δ44/40Ca, as Al and Na are unlikely to be present in carbonates. The samples with lower δ44/40Ca show higher CIA (Chemical Index of Alteration) values and Al/Ca than the UW diabase while samples having higher δ44/40Ca show lower CIA and Al/Ca than the UW diabase. The weathered sample having the lowest δ44/40Ca (close to the δ44/40Ca of plagioclase) exhibits the highest value of europium anomaly (Eu/Eu*). These observations are explained by the presence of variable relative proportions of residual clinopyroxene and plagioclase, the two dominant mineral phases in the weathered diabase, due to selective weathering of these minerals. Since plagioclase and clinopyroxene could not be separated from the diabase, we measured the Ca isotopic compositions of a clinopyroxene (δ44/40Ca = 1.06‰) from the San Carlos mantle peridotite and plagioclase from the Chilka anorthosite complex (δ44/40Ca = 0.40‰) from the Eastern Ghats and used these isotopic values as representative of the compositions of these minerals in the diabase. Based on mixing models, using δ44/40Ca, Al/Ca and Sr/Ca of the plagioclase and clinopyroxene end-members, we estimate that the δ44/40Ca of the UW diabase can be explained by 31% clinopyroxene and 69% plagioclase, which is consistent with the modal proportion of these minerals in an average diabase. Based on mixing calculations, the δ44/40Ca, Sr/Ca and Al/Ca variability of the micro-drilled samples of the weathered diabase are explained by the presence of varying proportions of residual clinopyroxene (20–65%) and plagioclase (80–35%) in the weathered rock. This study demonstrates that selective weathering of major rock-forming minerals in nature can result in significant variation in δ44/40Ca in weathered rocks and has implications for understanding the δ44/40Ca variability in rivers.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.031
  • Comparison of δ18O analyses on individual planktic foraminifer (Orbulina
           universa) shells by SIMS and gas-source mass spectrometry
    • Authors: Jody B. Wycech; Daniel Clay Kelly; Reinhard Kozdon; Ian J. Orland; Howard J. Spero; John W. Valley
      Abstract: Publication date: Available online 22 February 2018
      Source:Chemical Geology
      Author(s): Jody B. Wycech, Daniel Clay Kelly, Reinhard Kozdon, Ian J. Orland, Howard J. Spero, John W. Valley
      The oxygen isotope (δ18O) compositions of final chamber fragments of individual shells of the planktic foraminifer Orbulina universa were measured in situ via secondary ion mass spectrometry (SIMS) and by traditional gas-source mass spectrometry (GSMS) entailing acid digestion of sampled calcite. The paired SIMS-GSMS analyses were performed on final chamber fragments of fossil shells taken from the top of a sediment core (Holocene) as well as shells grown in laboratory culture. Multiple iterations of SIMS-GSMS analyses were conducted on final chamber fragments treated with a variety cleaning protocols. The series of paired analyses yielded an average SIMS-GSMS δ18O offset (Δ18OSIMS-GSMS) of −0.9 ± 0.1‰ (±2 SE). The volume of material analyzed in 10-μm SIMS spots is ~105 times smaller than that analyzed by GSMS; hence, the extent to which these Δ18OSIMS-GSMS values represent real differences in analyte vs. instrumental factors remains unclear. Possible contributing factors to the SIMS-GSMS δ18O difference include sample-standard mismatch by SIMS, differences in standardization of SIMS and GSMS, and non-calcite contaminants in samples. Although the two datasets are consistently offset, SIMS values reproduce inter-shell δ18O variability delineated by shell fragment GSMS values. This strong positive covariance proved useful for bringing the two datasets into agreement (i.e. Δ18OSIMS-GSMS = 0), and confirms that SIMS-based foraminifer δ18O values record changes in calcification temperature and/or δ18O of seawater. Whether shells of foraminifer taxa with differing microcrystalline structures, chemical composition, and/or preservation histories register a similar Δ18OSIMS-GSMS value is a subject of ongoing testing.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.028
  • Reprint of Comparison of climate signals obtained from encrusting and
           free-living rhodolith coralline algae
    • Authors: Siobhan Williams; Jochen Halfar; Thomas Zack; Steffen Hetzinger; Martin Blicher; Thomas Juul-Pedersen
      Abstract: Publication date: Available online 22 February 2018
      Source:Chemical Geology
      Author(s): Siobhan Williams, Jochen Halfar, Thomas Zack, Steffen Hetzinger, Martin Blicher, Thomas Juul-Pedersen
      Coralline algae have been used for sclerochronological studies throughout the last decade. These studies have focused on two different growth morphologies of the photosynthetic coralline algae: massive crusts forming small buildups on hard substrate, and free-living branching algal nodules, known as rhodoliths. The latter are generally found on soft-substrate, where they are frequently overturned by water movement and bottom feeding organisms, leaving one side of the rhodolith partially buried in the sediment at any given time. Here we test whether either of these growth morphologies is more suitable for proxy reconstructions by comparing Mg/Ca ratios – a temperature proxy – in multiple replicates of rhodoliths of Lithothamnion glaciale and in rhodoliths as well as encrusting specimens of Clathromorphum compactum. With both species being widespread throughout the Temperate and Arctic regions, we have chosen two North Atlantic localities at Nuuk Fjord, Greenland (Subarctic), and off the southeastern coast of Newfoundland, Canada (Temperate), for this study. Two to three Mg/Ca ratio transects spanning 18years of growth were analysed on multiple specimens with encrusting morphologies and along different sides of rhodoliths using laser ablation inductively coupled mass spectrometry and compared to remotely sensed sea surface temperature (SST) data. The length of the common time span used for comparison was limited by growth interruptions in rhodoliths. Furthermore, our comparison is based on the assumption that rhodolith growth increments are annual – an assumption that has recently been challenged by mesocosm studies. Monthly Mg/Ca values from multiple transects within each individual were compared and in samples from Nuuk fjord significant correlations were found in 4 of 4 encrusting C. compactum, 4 of 4 C. compactum rhodoliths, and 2 of 3 L. glaciale rhodoliths. In Newfoundland significant correlations were found in 6 of 6 encrusting C. compactum comparisons (average: r=0.61, p<0.001), and in 6 of 6 L. glaciale rhodolith comparisons (average: r=0.43, p<0.001) for monthly resolved time series. The monthly Mg/Ca ratios (n=216) from each morphology were compared with instrumental Reynolds SST yielding the following correlations: encrusting C. compactum (r=0.64, p<0.001), C. compactum rhodolith (r=0.62, p<0.001) and L. glaciale (r=0.58, p<0.001). In Newfoundland both morphologies indicate a similar strength in recording SST: encrusting C. compactum (r=0.85, p<0.001) and rhodolith-forming L. glaciale (r=0.84, p<0.001). In summary, Mg/Ca ratios derived from both coralline algal growth forms can yield SST information, however, massive encrusting forms generally yield higher correlations to SST than transects measured on individual rhodoliths, which only allowed for the generation of short uninterrupted time series due to frequent growth irregularities.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.030
  • Unexpected isotopic variability in biogenic aragonite: A user issue or
           proxy problem'
    • Authors: J. Madelyn Mette; M. Nina Whitney; Jared Ballew; Alan D. Wanamaker
      Abstract: Publication date: Available online 21 February 2018
      Source:Chemical Geology
      Author(s): J. Madelyn Mette, M. Nina Whitney, Jared Ballew, Alan D. Wanamaker
      The present study seeks to investigate sources of isotopic variability in the commonly used paleoclimate archive, the marine bivalve Arctica islandica, with an emphasis on the potential of human-induced variability arising from sampling techniques. Stable carbon (δ13Ccarbonate) and oxygen (δ18Ocarbonate) isotopes were analyzed for split (intra-sample) and replicate (intra- and inter-shell) samples taken from a group of laboratory-reared individuals, a natural population from northern Norway, and a natural population from the Gulf of Maine, USA. Compared to analytical uncertainty of 0.17‰ and 0.30‰ for δ13C and δ18O, respectively, among the natural populations, the mean difference between shell splits and shell replicates ranged from 0.12‰ and 0.33‰ for δ13C and δ18O, respectively. Our data suggest that heterogeneity of the carbonate material (i.e., large range of isotopic composition within one sample due to seasonal environmental variability) may contribute to “unexpected” variability more than human-induced error from sampling imprecision when collecting whole annual increments. Furthermore, δ13C from juvenile shells were highly variable (2σ standard deviation = 0.65‰), approximately four times more variable than analytical precision. High precision among δ18O measurements of the laboratory-reared shells confirm the presumption that shells reliably and consistently precipitate in isotopic equilibrium with ambient seawater. Monte Carlo simulations of measurements from this population allowed characterization of improvements in uncertainty at increasing levels of replication. Substantial reduction in uncertainty occurs when increasing from two to three shells, however replication using a total of four shells further decreased uncertainty to within the 99% confidence level. Published studies sometimes compensate for uncertainties by replicating records over multiple individuals or multiple transects within the one individual. Oftentimes, however, isotope records are constructed from single individuals or transects and therefore fail to provide thorough estimates of proxy error. Our findings suggest that replication of carbon and oxygen isotope measurements of contemporaneously produced aragonite is necessary in order to reduce proxy-derived noise. Furthermore, population-specific estimates of uncertainty related to natural variability among individuals should be investigated in order to provide more realistic representations of proxy noise when reporting isotope time series.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.027
  • Long-lived coralline alga records multidecadal variability in Labrador Sea
           carbon isotopes
    • Authors: A. Hou; J. Halfar; W. Adey; U.G. Wortmann; Z. Zajacz; A. Tsay; B. Williams; P. Chan
      Abstract: Publication date: Available online 21 February 2018
      Source:Chemical Geology
      Author(s): A. Hou, J. Halfar, W. Adey, U.G. Wortmann, Z. Zajacz, A. Tsay, B. Williams, P. Chan
      While the recent decline in the δ13C composition of oceanic dissolved inorganic carbon (DIC) can be attributed to increasing anthropogenic CO2 emissions (13C Suess effect), the causes of natural variability in the δ13C of oceanic DIC (δ13CDIC) are far less understood. Unfortunately, instrumental oceanic DIC measurements are not available prior to the 1970s, prohibiting the observation and study of long-term variability in oceanic carbon isotope dynamics. Thus, in order to identify the main driving forces of changes in oceanic δ13CDIC, multicentury carbon isotope time series that extend from the present into the preindustrial period are required. Such time series may be extracted from the carbonate skeletons of long-lived marine organisms, which have been shown to be robust recorders of fluctuations and trends in oceanic δ13CDIC. In this study, we use an annually-banded coralline alga live-collected from the Labrador shelf to generate a 266-year time series of δ13CDIC changes in the Labrador Sea. Our results indicate that from the 1960s onwards, the rate of δ13CDIC decline in the Labrador Sea slightly exceeds the rate of δ13C decline in the atmosphere, providing support for the enhanced CO2 uptake ability of the Labrador Sea. In addition, the detrended algal δ13C time series displays multidecadal variability with typical Atlantic Multidecadal Oscillation (AMO) frequencies. We show that prior to the late 1980s, algal δ13C compositions significantly correlate with regional sea ice cover (SIC) variability, post-1850 instrumental, reconstructed AMO indices, and solar variability. We speculate that these low-frequency oscillations in δ13C reflect changes in marine primary productivity modulated by a mechanism involving solar changes, the AMO and SIC variability. Our algal carbon isotope time series suggests that while the anthropogenic Suess effect has influenced Labrador Sea δ13CDIC since the 1960s, its influence may have been obscured by the effects of natural climatic variability up until the late 1980s.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.026
  • Dolomite dissolution kinetics in aqueous solutions in the presence of
           organic and inorganic additives at 25 °C and pCO2 ~ 1 atm
    • Authors: Sanoopkumar Puthiya Veetil; Alfonso Mucci; Takeshi Arakaki
      Abstract: Publication date: Available online 21 February 2018
      Source:Chemical Geology
      Author(s): Sanoopkumar Puthiya Veetil, Alfonso Mucci, Takeshi Arakaki
      The steady-state dissolution rate of dolomite was studied at 25 °C and 1 atm CO2 total pressure in deionised water in the absence (control) and presence of twenty seven different organic and inorganic additives at low concentration (1 mM). These additives are most likely present at low concentrations (<mM) in CO2 storage aquifers where they may inhibit or catalyze carbonate mineral dissolution kinetics. Dissolution experiments were carried out in “free drift” mode and the rates were expressed in terms of leaching of Ca and Mg to the solution with time. Results of the present experiments show that the dolomite dissolution rate is negligibly affected by most of the investigated additives at 1 mM. The dissolution rate was strongly inhibited and proceeded incongruently in the presence of nucleotides and inorganic phosphate salts, yielding a Mg:Ca solution ratio ≥ 2. The formation of a solid phosphate phase on the dolomite surface, likely a Ca-rich phosphate, is responsible for this observed inhibition and incongruency. In contrast, the presence of EDTA, citrate, glutamate and serine significantly enhanced the dissolution rate of dolomite. The catalytic effectiveness of EDTA increased linearly with its concentration whereas the inhibitory effectiveness of diphosphate was a non-linear function of its concentration.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.025
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