Geological Sciences

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A new Late Devonian flora from Sonid Zuoqi, Inner Mongolia, northeastern China
(Cambridge University Press, 2021-10) Bai, Lingqi; Huang, Pu; Yang, Ning; Ju, Wenxin; Liu, Jianbo; Basinger, James F.; Xu, Honghe; Xue, Jinzhuang
The Silurian and Devonian plant fossil record is the basis for our understanding of the early evolution of land plants, yet our appreciation of early global phytogeographic evolution has been constrained by the focus of most studies on deposits from Europe, North America, and, more recently, South China. Devonian plants have been recorded rarely from northeastern China, and among previous records, few plants have been illustrated and formally described. In this article, megafossil plants representing a Late Devonian-aged (probably Famennian) flora are described from a locality at northern Sonid Zuoqi, Inner Mongolia, NE China. The flora includes Melvillipteris sonidia new species, Archaeopteris sp., and fragments of some other plants. The new plant shows main axes and two orders of lateral branches. The first-order branches of this plant show a typical zigzag appearance and are borne in pairs on main axes. Second-order branches are straight or slightly flexed, and are borne helically or alternately on first-order branches. Sterile ultimate appendages and fertile structures of M. sonidia n. sp. are borne alternately on second-order branches. An associated palynological assemblage, as well as U-Pb ages of detrital zircon grains from adjacent horizons, are also reported, indicating a Late Devonian age in accord with the megafossil plants. The present study contributes to our appreciation of the Devonian floristic diversity of the Xing'an Block, and, through our review of the record of early vascular plants from NE China, more broadly to the understanding of the mid-latitude vegetation of the Northern Hemisphere during the Late Devonian.
A review of paleobotanical studies of the Early Eocene Okanagan (Okanogan) Highlands floras of British Columbia, Canada, and Washington, USA
(Canadian Science Publishing, 2016-02) Greenwood, David R.; Pigg, Kathleen B.; Basinger, James F.; DeVore, Melanie L.
The history of plant fossil collecting in the Okanagan (Okanogan) Highlands of British Columbia and northeastern Washington is closely intertwined with the history of geological surveys and mining activities from the 1870s onward. The first descriptions of fossil plants from British Columbia were published in 1870–1920 by J.W. Dawson, G.M. Dawson, and D.P. Penhallow. In the United States, fossil leaves and fish were first recognized at Republic, Washington, by miners in the early 1900s. Many early workers considered these floras to be of Oligocene or Miocene age. C.A. Arnold described Canadian occurrences of conifers and Azolla in the 1950s. Palynological studies in the 1960s by L.V. Hills, G.E. Rouse, and others and those of fossil fish by M.V.H. Wilson in the 1970–1980s provided the framework for paleobotanical research at several key localities. Permineralized plants were first described from the Princeton chert in the 1970s by C.N. Miller, J.F. Basinger, and others, followed by R.A. Stockey and her students. W.C. Wehr and K.R. Johnson revitalized the study of fossils at Republic with the discovery of a diverse assemblage in 1977. In 1987, J.A. Wolfe and Wehr produced a United States Geological Survey monograph on Republic, and Wehr cofounded the Stonerose Interpretive Center as a venue for public collecting. Systematic studies of the Okanagan Highlands plants, as well as paleoecological and paleoclimate reconstructions from palynomorphs and leaf floras, continue to expand our understanding of this important Early Eocene assemblage.
Acidic microenvironments in waste rock characterized by neutral drainage: Bacteria-mineral interactions at sulfide surfaces
(MDPI, 2014-03-21) Dockrey, John W.; Lindsay, Matthew B. J.; Mayer, K. Ulrich; Beckie, Roger D.; Norlund, Kelsey L. I.; Warren, Lesley; Southam, Gordon
Microbial populations and microbe-mineral interactions were examined in waste rock characterized by neutral rock drainage (NRD). Samples of three primary sulfide-bearing waste rock types (i.e., marble-hornfels, intrusive, exoskarn) were collected from field-scale experiments at the Antamina Cu–Zn–Mo mine, Peru. Microbial communities within all samples were dominated by neutrophilic thiosulfate oxidizing bacteria. However, acidophilic iron and sulfur oxidizers were present within intrusive waste rock characterized by bulk circumneutral pH drainage. The extensive development of microbially colonized porous Fe(III) (oxy)hydroxide and Fe(III) (oxy)hydroxysulfate precipitates was observed at sulfide-mineral surfaces during examination by field emission-scanning electron microscopy-energy dispersive X-ray spectroscopy (FE-SEM-EDS). Linear combination fitting of bulk extended X-ray absorption fine structure (EXAFS) spectra for these precipitates indicated they were composed of schwertmannite [Fe8O8(OH)6–4.5(SO4)1–1.75], lepidocrocite [γ-FeO(OH)] and K-jarosite [KFe3(OH)6(SO4)2]. The presence of schwertmannite and K-jarosite is indicative of the development of localized acidic microenvironments at sulfide-mineral surfaces. Extensive bacterial colonization of this porous layer and pitting of underlying sulfide-mineral surfaces suggests that acidic microenvironments can play an important role in sulfide-mineral oxidation under bulk circumneutral pH conditions. These findings have important implications for water quality management in NRD settings.
Adsorption of (Poly)vanadate onto Ferrihydrite and Hematite: An In Situ ATR–FTIR Study
(American Chemical Society (ACS) Publications, 2020-03-25) Vessey, Colton; Schmidt, Michael P.; Abdolahnezhad, Mojtaba; Peak, Derek; Lindsay, Matthew B. J.
Vanadium (V) has been a useful trace metal in describing Earth’s biogeochemical cycling and development of industrial processes; however, V has recently been recognized as a potential contaminant of concern. Although Fe (oxyhydr)oxides are important sinks for aqueous V in soils and sediments, our understanding of adsorption mechanisms is currently limited to mononuclear species (i.e., HxVO4(3–x)–). Here we use in situ attenuated total reflectance – Fourier transform infrared spectroscopy to examine sorption mechanisms and capacity for (poly)vanadate attenuation by ferrihydrite and hematite from pH 3 to 6. Adsorption isotherms illustrate the low affinity of polyvanadate species for ferrihydrite surfaces compared to hematite. Mononuclear V species (i.e., [HxVO4](3−x)− and VO2+) were present at all experimental conditions. At low surface loadings and pH 5 and 6, H2VO4− adsorption onto ferrihydrite and hematite surfaces results from formation of inner sphere complexes. At [V]T above 250 µM, adsorbed polynuclear V species in this study include H2V2O72− and V4O124−. Whereas, HV10O286−, H3V10O285−, and NaHV10O284− are the predominant adsorbed species at pH 3 and 4 and elevated [V]T. Surface polymers were identified on hematite at all experimental pH values, whereas polymeric adsorption onto ferrihydrite was limited to pH 3 and 4. These results suggest that hematite offers a more suitable substrate for polymer complexation compared to ferrihydrite. Our results demonstrate the pH and concentration dependant removal of (poly)vanadate species by Fe(III) (oxyhydr)oxides, which has implications for understanding V mobility, behaviour, and fate in the environment.
Alum addition triggers hypoxia in an engineered pit lake
(MDPI, 2022-02-26) Jessen, Gerdhard L.; Chen, Lin-Xing; Mori, Jiro F.; Colenbrander Nelson, Tara E.; Slater, Gregory F.; Lindsay, Matthew B. J.; Banfield, Jillian F.; Warren, Lesley A.
Here, we examine the geobiological response to a whole-lake alum (aluminum sulfate) treatment (2016) of Base Mine Lake (BML), the first pilot-scale pit lake established in the Alberta oil sands region. The rationale for trialing this management amendment was based on its successful use to reduce internal phosphorus loading to eutrophying lakes. Modest increases in water cap epilimnetic oxygen concentrations, associated with increased Secchi depths and chlorophyll-a concentrations, were co-incident with anoxic waters immediately above the fluid fine tailings (FFT) layer post alum. Decreased water cap nitrate and detectable sulfide concentrations, as well as increased hypolimnetic phospholipid fatty acid abundances, signaled greater anaerobic heterotrophic activity. Shifts in microbial community to groups associated with greater organic carbon degradation (i.e., SAR11-LD12 subclade) and the SRB group Desulfuromonodales emerged post alum and the loss of specialist groups associated with carbon-limited, ammonia-rich restricted niches (i.e., MBAE14) also occurred. Alum treatment resulted in additional oxygen consumption associated with increased autochthonous carbon production, watercap anoxia and sulfide generation, which further exacerbate oxygen consumption associated with on-going FFT mobilized reductants. The results illustrate the importance of understanding the broader biogeochemical implications of adaptive management interventions to avoid unanticipated outcomes that pose greater risks and improve tailings reclamation for oil sands operations and, more broadly, the global mining sector.
An anomalous shallow-marine ichnofacies gradient from the Lower Devonian Talacasto Formation of the Argentine Precordillera
(Palaeogeography, Palaeoclimatology, Palaeoecology, 2025-01) Wenger, Federico D.; Buatois, Luis A.; Mángano, M. Gabriela; Muñoz, Diego F.; Rustán, Juan J.
The Lower Devonian Talacasto Formation in western Argentina records deposition in wave-dominated shallow-marine environments. This unit comprises a large-scale progradational succession, transitioning from black, parallel-laminated mudstone in the lower interval to siltstone and very fine- to medium-grained sandstone in the upper interval. The succession spans environments ranging from the shelf to the upper shoreface. Three trace-fossil assemblages have been identified: (1) Palaeophycus assemblage, including Palaeophycus heberti, P. tubularis, and Helminthopsis isp., corresponding to the shelf; (2) Phycosiphon-Zoophycos assemblage with Zoophycos isp., Phycosiphon incertum, Nereites missouriensis, and Chondrites isp., ranging from the lower offshore to the lower/middle shoreface; and (3) Rosselia assemblage containing Rosselia socialis, Skolithos isp., Arenicolites isp., Palaeophycus tubularis, and escape trace fossils, corresponding to the offshore transition and the lower/middle shoreface. Two ichnofacies have been identified: distal Cruziana and Skolithos Ichnofacies. Unlike the traditional ichnofacies model, the Talacasto Formation shows an onshore expansion of the distal Cruziana Ichnofacies, which is present not only in the lower offshore, but in the upper offshore, offshore transition, and lower shoreface as well. In contrast, the archetypal Cruziana Ichnofacies is not present. This anomalous distribution is attributed to an interplay of ecologic and taphonomic factors combined with the restricted topography of the southern portion of the Precordillera Basin. Low-energy conditions and high food supply for prolonged times allowed for the obliteration of shallow-tier trace fossils by deeper and widely distributed burrows, favoring the onshore expansion of the distal Cruziana Ichnofacies and preventing the preservation of the typical elements of the archetypal Cruziana Ichnofacies. Areas subjected to greater storm influence provided favorable conditions for the development of the Skolithos Ichnofacies.
Analytical formulas for geometrical factor and sensitivity for long electrodes
(Wiley, 2024-11-22) Butler, S.L.
In the electrical resistivity method, electrodes are usually modelled as point current sources and point voltage measurements. If the burial depth of the electrode is significant compared with the spacing between electrodes, this point approximation may not be accurate. Common situations employing long electrodes include the use of metal-cased boreholes as electrodes and small-scale, high-resolution environmental, engineering and archaeological surveys where electrode spacings may be very small. In this contribution, I present analytical expressions for the mutual resistance between long electrodes modelled as line current sources. Mutual resistances are then used to calculate geometrical factors. Additionally, I present an expression for the current density and use it to derive an analytical expression for the sensitivity of electrode arrays with long electrodes. The sensitivity is, in turn, used to calculate the mean depth and position which can be used as estimates of depth and position of investigation and as pseudosection plot points. Example calculations using the geometrical factor, sensitivity and mean depth are shown, and comparisons are made with simulations and lab-scale experiments.
Aqueous vanadate removal by iron(II)-bearing phases under anoxic conditions
(American Chemical Society (ACS) Publications, 2020-03-06) Vessey, Colton; Lindsay, Matthew B. J.
Vanadium contamination is a growing environmental hazard worldwide. Aqueous vanadate (HxVVO4(3−x)− (aq)) concentrations are often controlled by surface complexation with metal (oxyhydr)oxides in oxic environments. However, the geochemical behaviour of this toxic redox sensitive oxyanion in anoxic environments is poorly constrained. Here we describe results of batch experiments to determine kinetics and mechanisms of aqueous H2VVO4− (100 μM) removal under anoxic conditions in suspensions (2.0 g L−1) of magnetite, siderite, pyrite, and mackinawite. We present results of parallel experiments using ferrihydrite (2.0 g L−1) and Fe2+(aq) (200 μM) for comparison. Siderite and mackinawite reached near complete removal (46 µmol g−1) of aqueous vanadate after 3 h and kinetic rates were generally consistent with ferrihydrite. Whereas magnetite removed 18 µmol g−1 of aqueous vanadate after 48 h and uptake by pyrite was limited. Uptake by Fe2+(aq) was observed after 8 h, concomitant with precipitation of secondary Fe phases. X ray absorption spectroscopy revealed V(V) reduction to V(IV) and formation of bidentate corner-sharing surface complexes on magnetite and siderite, and with Fe2+(aq) reaction products. These data also suggest that V(IV) is incorporated into the mackinawite structure. Overall, we demonstrate that Fe(II)-bearing phases can promote aqueous vanadate attenuation and, therefore, limit dissolved V concentrations in anoxic environments.
Aqueous- and solid-phase molybdenum geochemistry of oil sands fluid petroleum coke deposits, Alberta, Canada
(Elsevier, 2018-11-12) Robertson, Jared M.; Nesbitt, Jake A.; Lindsay, Matthew B. J.
Fluid petroleum coke generated at oil sands operations in the Athabasca Oil Sands Region of northern Alberta, Canada, contains elevated concentrations of molybdenum (Mo) and other metals including nickel (Ni) and vanadium (V). Solid-phase Mo concentrations in fluid petroleum coke are typically 10 to 100 times lower than V and Ni, yet dissolved Mo concentrations in associated pore waters are often comparable with these metals. We collected pore water and solids from fluid petroleum coke deposits in the AOSR to examine geochemical controls on Mo mobility. Dissolved Mo concentrations increased with depth below the water table, reaching maxima of 1.4 to 2.2 mg L-1, within a mixing zone between slightly acidic and oxic meteoric water and mildly alkaline and anoxic oil sands process-affected water (OSPW). Dissolved Mo concentrations decreased slightly with depth below the mixing zone. X-ray absorption spectroscopy revealed that Mo(VI) and Mo(IV) species were present in coke solids. The Mo(VI) occurred as tetrahedrally coordinated MoO42- adsorbed via inner- and outer-sphere complexation, and was coordinated in an environment similar to Fe-(hydr)oxide surface complexes. The OSPW likely promoted desorption of outer-sphere Mo(VI) complexes, resulting in higher dissolved Mo concentrations in the mixing zone. The principal Mo(IV) species was MoS2, which originated as a catalyst added upstream of the fluid coking process. Although MoS2 is likely stable under anoxic conditions below the mixing zone, oxidative weathering in the presence of meteoric water may promote long-term Mo release.
Bellerophontid molluscs in the Grimsby Formation (Llandovery, lower Silurian), Hamilton, Ontario, Canada and their paleoecological and taphonomic implications
(Canadian Science Publishing, 2024-08-01) Pratt, Brian R.; Hopkins, Graeme J.; Hopkins, Richard J.
Specimens of a small bellerophontid mollusc, considered conspecific with Planorbis bilobatus Conrad 1839 from coeval strata in New York State, were recovered from the Grimsby Formation (lower Llandovery, lower Silurian), exposed in the Niagara Escarpment of western Hamilton, Ontario. Because Conrad’s species name is pre-occupied and is a secondary homonym, the new material is assigned to Tritonophon grimsbyensis n. sp. As Conrad’s original specimens are lost and where he collected them is unknown, a neotype from the Grimsby Formation is designated. These bellerophonts are preserved as casts on the soles of thin, fine-grained, sandstone beds interbedded with shale. These beds are probably tempestites Most are juvenile forms oriented on their sides, but in some beds adults with a widely expanded aperture are oriented aperture-down. Some specimens exhibit a V-shaped sinus on the median lobe, which is rarely preserved in Silurian examples. The aperture-down orientation suggests that this was the stable position during gentle wave action as well as probably their life position. Beds containing only juveniles may be evidence that the bellerophonts occasionally experienced a population boom but then were killed off during the storm event. Fine-grained sandstone fills the shell interiors, likely emplaced during wave-induced agitation. However, the shell walls are cast in mudstone, indicating that they dissolved during shallow burial and mud was pumped into the moulds. This may have been aided by episodic ground motion due to earthquakes that mobilized the adjacent sediment.
Benchmarking multiphysics software for mantle convection
(Elsevier, 2021-09) Trim, Sean; Butler, Samuel; Spiteri, Raymond
Numerical simulations are a highly valuable tool for improving our understanding of mantle dynamics. COMSOL Multiphysics® is a commercial software suite designed to numerically model experiments featuring multiple branches of physics. This modeling approach applies to mantle convection, which can be viewed as a combination of fluid dynamics and thermodynamics. COMSOL® is of interest to the geoscience community due to its ease of use compared to other available codes, and it has been used in previous mantle convection studies. However, COMSOL® has not been extensively benchmarked for mantle convection. In this study, we confirm the accuracy of COMSOL® against several established benchmarks pertaining to a variety mantle convection features and geometries. Overall, we find reasonable agreement between the results from COMSOL® and reported benchmark data. This study may also serve the geoscience community as a guide for using COMSOL® to model mantle convection.
Bioturbators as ecosystem engineers in space and time
(Palaeontology, 2024) Mangano, Maria Gabriela; Buatois, Luis; Minter, Nicholas John; Gougeon, Romain
Biogenic sedimentary structures offer a unique perspective for understanding the role of the biosphere in the interaction with other Earth subsystems and the building up of our planet. The record of their ancient equivalents provides a wealth of information for reconstructing the role of bioturbators as ecosystem engineers using multiple ichnological proxies and methods. In this study, we present an overview of how bioturbation has worked across a broad range of spatial and temporal scales from the perspective of ecosystem engineering. Comprehensive and systematic datasets allow analyses at regional and global spatial extents, and especially over long temporal scales where sampling intensity and rock record biases can be considered. Our results underscore the significance of the Cambrian Explosion in the establishment of modern-style shallow marine ecosystems and of the Ordovician Radiation for their deep marine counterparts, as well as the continuous ecosystem impact of bioturbation during Palaeozoic terrestrialization. Comparable datasets for the rest of the Phanerozoic have not yet been compiled. However, preliminary information indicates that colonization of ultra-deep tiers, the rise to prominence of regenerators, increased burrowing efficiency, and increased compartmentalization of the endobenthic ecospace, were products of the Mesozoic Marine Revolution. The trace-fossil record offers hard data to evaluate bioturbation as a driving force in ecosystem re-structuring and as a key factor in geobiological cycles. Models assessing these fundamental issues should be rooted empirically at different scales, from both autoecological and synecological to macroecological, making the best possible use of the rich and rapidly developing ichnological toolbox.
Chemical mass transport between fluid fine tailings and the overlying water cover of an oil sands end pit lake
(American Geophysical Union, 2017-05-17) Dompierre, Kathryn A.; Barbour, S. Lee; North, Rebecca L.; Carey, Sean K.; Lindsay, Matthew B. J.
Fluid fine tailings (FFT) are a principal by-product of the bitumen extraction process at oil sands mines. Base Mine Lake (BML)—the first full-scale demonstration oil sands end pit lake (EPL)—contains approximately 1.9 3 108 m^3 of FFT stored under a water cover within a decommissioned mine pit. Chemical mass transfer from the FFT to the water cover can occur via two key processes: (1) advection-dispersion driven by tailings settlement; and (2) FFT disturbance due to fluid movement in the water cover. Dissolved chloride (Cl) was used to evaluate the water cover mass balance and to track mass transport within the underlying FFT based on field sampling and numerical modeling. Results indicated that FFT was the dominant Cl source to the water cover and that the FFT is exhibiting a transient advection-dispersion mass transport regime with intermittent disturbance near the FFT-water interface. The advective pore water flux was estimated by the mass balance to be 0.002 m^3 m^-2 d^-1, which represents 0.73 m of FFT settlement per year. However, the FFT pore water Cl concentrations and corresponding mass transport simulations indicated that advection rates and disturbance depths vary between sample locations. The disturbance depth was estimated to vary with location between 0.75 and 0.95 m. This investigation provides valuable insight for assessing the geochemical evolution of the water cover and performance of EPLs as an oil sands reclamation strategy.
Co-expression of multi-genes for polynary perovskite electrocatalysts for reversible solid oxide cells
(Springer Nature, 2025-03-25) Zhang, Xiaoxin; He, Hongyuan; Chen, Yu; Yang, Guangming; Xiao, Xiao; Lv, Haiping; Xiang, Yongkang; Wang, Shuxiong; Jiang, Chang; Li, Jianhui; Chen, Zhou; Liu, Subiao; Yan, Ning; Yong, Xue; Alodhayb, Abdullah N.; Pan, Yuanming; Chen, Ning; Lin, Jinru; Tu, Xin; Shao, Zongping; Sun, Yifei
High-entropy LnBaCo2O5+δ perovskites are explored as rSOC air electrodes, though high configuration entropy (Sconfig) alone poorly correlates with performance due to multifactorial interactions. We systematically engineer LnBaCo2O5+δ perovskites (Ln = lanthanides) with tunable Sconfig and 20 consistent parameters, employing Bayesian-optimized symbolic regression to decode activity descriptors. The model identifies synergistic contributions from Sconfig, ionic radius, and electronegativity, enabling screening of 177,100 compositions. Three validated oxides exhibit superior activity/durability, particularly (Pr0.05La0.4Nd0.2Sm0.1Y0.25)BaCo2O5+δ, showing enhanced oxygen vacancy concentration and disordered transport pathways. First-principles studies reveal optimized charge transfer kinetics via cobalt-oxygen bond modulation. Further, the interplay between first ionization energy, atomic mass, and ionic Lewis acidity dictates stability. This data-driven approach establishes a quantitative framework bridging entropy engineering and catalytic functionality in complex oxides.
Dietary palaeoecology of an Early Cretaceous armoured dinosaur (Ornithischia; Nodosauridae) based on floral analysis of stomach contents
(The Royal Society Publishing, 2020-06) Brown, Caleb M.; Greenwood, David; Kalyniuk, Jessica E.; Braman, Dennis R.; Henderson, Donald M.; Greenwood, Cathy L.; Basinger, James F.
The exceptionally well-preserved holotype of the armoured dinosaur Borealopelta markmitchelli (Ornithischia; Nodosauridae) from the Early Cretaceous (Clearwater Formation) of northern Alberta preserves a distinct mass within the abdominal cavity. Fourteen independent criteria (including: co-allochthony, anatomical position, gastroliths) support the interpretation of this mass as ingested stomach contents—a cololite. Palynomorphs in the cololite are a subset of the more diverse external sample. Analysis of the cololite documents well-preserved plant material dominated by leaf tissue (88%), including intact sporangia, leaf cross-sections and cuticle, but also including stems, wood and charcoal. The leaf fraction is dominated (85%) by leptosporangiate ferns (subclass Polypodiidae), with low cycad–cycadophyte (3%) and trace conifer foliage. These data represent the most well-supported and detailed direct evidence of diet in an herbivorous dinosaur. Details of the dietary palaeoecology of this nodosaur are revealed, including: selective feeding on ferns; preferential ingestion of leptosporangiate ferns to the exclusion of Osmundaceae and eusporangiate ferns such as Marattiaceae; and incidental consumption of cycad–cycadophyte and conifer leaves. The presence of significant (6%) charcoal may represent the dietary use of recently burned conifer forest undergoing fern succession, early evidence of a fire succession ecology, as is associated with many modern large herbivores.
Discovery of Ge2+ in quartz: Evidence from EPR/XAS experiments and DFT calculations, and implications for Ge/Si systematics
(Geochimica et Cosmochimica Acta, 2025-01) Mashkovtsev, Rudolf I.; Botis, Sanda M.; Lin, Jinru; Deevsalar, Reza; Cheung, Leo Ka Long; Wiens, Eli; Tunc, Ayetullah; Chen, Ning; Chernikov, Roman; Pan, Yuanming
The Ge/Si systematics as a biogeochemical tracer with diverse applications from paleo-climatic reconstructions to discrimination of magma sources and elucidation of Earth’s early evolution hinges on the coherent behavior of these elements in the tetravalent state. However, determination of Ge speciation in quartz and other silicate minerals is technically challenging because this element almost invariably occurs at several parts per million or lower concentrations. This contribution reports a detailed study of Ge speciation in quartz by combining single-crystal electron paramagnetic resonance spectroscopy, synchrotron X-ray absorption spectroscopy, and ab initio theoretical calculations. Our single-crystal and powder electron paramagnetic resonance spectra of artificially irradiated quartz reveal a suite of previously reported Ge electron centers (GECs) such as [GeHLi2]0 and [GeHH2]0 centers as well as a new GeHLi center. These multiply-compensated GECs in artificially irradiated quartz suggest that their precursors before irradiation involve the diamagnetic Ge2+ state. Ge K-edge X-ray absorption spectroscopic data of selected quartz samples further support the presence of Ge2+. Theoretical calculations reproduce the experimental 1H and 7Li hyperfine constants of the [GeHLi2]0 center and suggest the new GeHLi center to be a new variant of the multiply-compensated GECs with the second monovalent cation in a distant c-axis channel, again supporting the Ge2+ state. The presence of Ge2+ in sedimentary-diagenetic quartz, in particular, challenges existing thermodynamic data that Ge4+ is the only stable oxidation state in aqueous solutions under near-surface conditions. Incorporation of Ge2+ in quartz and other silicates can significantly affect Ge/Si fractionations, with important implications for their applications as a biogeochemical tracer from surficial environments to magmatic-hydrothermal systems, Earth’s core-mantle differentiation, and other planetary processes.
Discovery of Ge2+ in quartz: Evidence from EPR/XAS experiments and DFT calculations, and implications for Ge/Si systematics
(Elsevier, 2025-03-15) Mashkovtsev, Rudolf I.; Botis, Sanda M.; Lin, Jinru; Deevsalar, Reza; Cheung, Leo Ka Long; Wiens, Eli; Tunc, Ayetullah; Chen, Ning; Chernikov, Roman; Pan, Yuanming
The Ge/Si systematics as a biogeochemical tracer with diverse applications from paleo-climatic reconstructions to discrimination of magma sources and elucidation of Earth’s early evolution hinges on the coherent behavior of these elements in the tetravalent state. However, determination of Ge speciation in quartz and other silicate minerals is technically challenging because this element almost invariably occurs at several parts per million or lower concentrations. This contribution reports a detailed study of Ge speciation in quartz by combining single-crystal electron paramagnetic resonance spectroscopy, synchrotron X-ray absorption spectroscopy, and ab initio theoretical calculations. Our single-crystal and powder electron paramagnetic resonance spectra of artificially irradiated quartz reveal a suite of previously reported Ge electron centers (GECs) such as [GeHLi2]0 and [GeHH2]0 centers as well as a new GeHLi center. These multiply-compensated GECs in artificially irradiated quartz suggest that their precursors before irradiation involve the diamagnetic Ge2+ state. Ge K-edge X-ray absorption spectroscopic data of selected quartz samples further support the presence of Ge2+. Theoretical calculations reproduce the experimental 1H and 7Li hyperfine constants of the [GeHLi2]0 center and suggest the new GeHLi center to be a new variant of the multiply-compensated GECs with the second monovalent cation in a distant c-axis channel, again supporting the Ge2+ state. The presence of Ge2+ in sedimentary-diagenetic quartz, in particular, challenges existing thermodynamic data that Ge4+ is the only stable oxidation state in aqueous solutions under near-surface conditions. Incorporation of Ge2+ in quartz and other silicates can significantly affect Ge/Si fractionations, with important implications for their applications as a biogeochemical tracer from surficial environments to magmatic-hydrothermal systems, Earth’s core-mantle differentiation, and other planetary processes.
Dissolved selenium(VI) removal by zero-valent iron under oxic conditions: Influence of sulfate and nitrate
(American Chemical Society, 2017-04-17) Das, Soumya; Lindsay, Matthew B. J.; Essilfie-Dughan, Joseph; Hendry, M. James
Dissolved Se(VI) removal by three commercially-available zero-valent irons (ZVIs) was examined in oxic batch experiments under circumneutral pH conditions in the presence and absence of NO3- and SO42-. Environmentally relevant Se(VI) (1 mg/L), NO3- ([NO3-N] = 15 mg/L) and SO42- (1800 mg/L) were employed to simulate mining-impacted waters. Ninety percent Se(VI) removal was achieved within 4 to 8 h in the absence of SO42- and NO3-. Similar Se(VI) removal was observed after 10 to 32 h in the presence of NO3-. Dissolved Se(VI) removal rates exhibited the greatest decrease in the presence of SO42-; 90% Se(VI) removal was measured after 50 to 191 h for SO42- and after 150 to 194 h for SO42- plus NO3- depending on the ZVI tested. Despite differences in removal rates among batches and ZVI materials, Se(VI) removal consistently followed first-order reaction kinetics. Scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analyses of reacted solids showed that Fe(0) present in ZVI undergoes oxidation to magnetite [Fe3O4], wüstite [FeO], lepidocrocite [γ-FeOOH], and goethite [α-FeOOH] over time. X-ray absorption near edge structure spectroscopy indicated that Se(VI) was reduced to Se(IV) and Se(0) during removal. These results demonstrate that ZVI can be effectively used control Se(VI) concentrations in mining impacted waters.
Ebullition enhances chemical mass transport across the tailings-water interface of oil sands pit lakes
(Elsevier, 2021-12-09) Francis, Daniel; Barbour, S. Lee; Lindsay, Matthew B. J.
Base Mine Lake (BML) was the first commercial-scale demonstration oil sands pit lake established in northern Alberta, Canada. Recent studies indicate that ebullition enhances internal mass loading of dissolved constituents during settlement and dewatering of methanogenic fine fluid tailings (FFT) below the overlying water cap. Here, we describe results of integrated field measurements and numerical modelling to (i) determine potential for ebullition and enhanced mixing within BML, and (ii) assess impacts on chemical mass transport across the tailings-water interface. We observed sharp increases in [CH4(aq)] with depth from < 0.1 mg L−1 immediately above the interface to > 60 mg L−1 over the upper 1.5 to 3.0 m of FTT. Thermodynamic modelling revealed that maximum [CH4(aq)] values represent 60 to 80 % of theoretical saturation, and corresponding total dissolved gas pressures approach or exceed fluid pressures. These findings supported integration of enhanced mixing into one-dimensional (1-D) advective-dispersive transport models, which substantially improved upon previous simulations of conservative tracer (i.e., Cl−) profiles and chemical mass fluxes. The models revealed a positive relationship between CH4(aq) saturation and enhanced mixing, showing that ebullition enhance internal mass loading. This information has potential to inform ongoing assessments of pit lake performance and support improved closure and reclamation planning at oil sands mines.
Endorhizal Fungi in Ranunculus from Western and Arctic Canada: Predominance of Fine Endophytes at High Latitudes
(Bentham Open Archives, 2010-01) Walker, X. J.; Basinger, J. F.; Kaminskyj, S. J. W.
Ranunculus roots were sampled across a latitudinal transect encompassing 52 °N and 82 °N, for years spanning 1963-2007. Samples from 2004 and later were preserved in formalin; earlier samples were taken from herbarium accessions. Roots were examined for colonization by arbuscular mycorrhizae, fine endophyte, and septate endophyte fungi using lactofuchsin-stained material imaged with epifluorescence microscopy. Endorhizal quantitation was assessed for each endorhizal morphotype. Roots from High Arctic (79 °N-82 °N) and mid-latitude (52 °N-54 °N) sites both contained all three endorhizal morphotypes; however, overall fungal colonization was almost three-fold higher in midlatitude samples. Most Ranunculus root colonization (29 % of the root length) in High Arctic samples was from fine endophyte fungi, whereas fine endophyte colonization was ∼ 20 % of root length in mid-latitude roots. In contrast, arbuscular mycorrhizal colonization was 2 % of root length in High Arctic samples and 57 % in mid-latitude samples. Septate endophyte colonization was 11 % and 36 % of root length for High Arctic and mid-latitude samples, respectively. These values are consistent with our previous results for other taxa, and suggest that fine endophytes are important contributors to soil microbial diversity as related to plant survival and competitiveness in the high latitudes.

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