scholarly journals Chromium Isotope Systematics in Modern and Ancient Microbialites

Minerals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 928 ◽  
Author(s):  
Sylvie Bruggmann ◽  
Alexandra S. Rodler ◽  
Robert M. Klaebe ◽  
Steven Goderis ◽  
Robert Frei
Keyword(s):  
Isotope Composition ◽  
Significant Proportion ◽  
Environmental Parameters ◽  
Mono Lake ◽  
Carbonate Sediments ◽  
Microbial Carbonates ◽  
Marine Carbonate ◽  
Physico Chemical ◽  
O Isotope ◽  
Study Sites

Changes in stable chromium isotopes (denoted as δ53Cr) in ancient carbonate sediments are increasingly used to reconstruct the oxygenation history in Earth’s atmosphere and oceans through time. As a significant proportion of marine carbonate older than the Cambrian is microbially-mediated, the utility of δ53Cr values in ancient carbonates hinges on whether these sediments accurately capture the isotope composition of their environment. We report Cr concentrations (Cr) and δ53Cr values of modern marginal marine and non-marine microbial carbonates. These data are supported by stable C and O isotope compositions, as well as rare earth elements and yttrium (REY) concentrations. In addition, we present data on ancient analogs from Precambrian strata. Microbial carbonates from Marion Lake (Australia, δ53Cr ≈ 0.99‰) and Mono Lake (USA, ≈0.78‰) display significantly higher δ53Cr values compared with ancient microbialites from the Andrée Land Group in Greenland (720 Ma, ≈0.36‰) and the Bitter Springs Formation in Australia (800 Ma, ≈−0.12‰). The δ53Cr values are homogenous within microbialite specimens and within individual study sites. This indicates that biological parameters, such as vital effects, causing highly variable δ53Cr values in skeletal carbonates, do not induce variability in δ53Cr values in microbialites. Together with stable C and O isotope compositions and REY patterns, δ53Cr values in microbialites seem to be driven by environmental parameters such as background lithology and salinity. In support, our Cr and δ53Cr results of ancient microbial carbonates agree well with data of abiotically precipitated carbonates of the Proterozoic. If detrital contamination is carefully assessed, microbialites have the potential to record the δ53Cr values of the waters from which they precipitated. However, it remains unclear if these δ53Cr values record (paleo-) redox conditions or rather result from other physico-chemical parameters.

scholarly journals Estimating Environmental Contamination and Element Deposition at an Urban Area of Central Italy

Urban Science ◽  
2019 ◽  
Vol 3 (3) ◽  
pp. 76 ◽  
Author(s):  
Stefano Loppi ◽  
Adelmo Corsini ◽  
Luca Paoli
Keyword(s):  
Urban Area ◽  
Environmental Contamination ◽  
Urban Areas ◽  
Central Italy ◽  
Protective Role ◽  
Evernia Prunastri ◽  
Physico Chemical ◽  
Living Organisms ◽  
Study Sites ◽  
Economic Constraints

Air quality monitoring in many urban areas is based on sophisticated and costly equipment to check for the respect of environmental quality standards, but capillary monitoring is often not feasible due to economic constraints. In such cases, the use of living organisms may be very useful to complement the sparse data obtained by physico-chemical measurements. In this study, the bioaccumulation of selected trace elements (Al, As, Cd, Ce, Cr, Cu, Fe, Ni, Pb, S, Sb, Zn) in lichen samples (Evernia prunastri) transplanted for three months at an urban area of Central Italy was investigated to assess the main environmental contaminants, their sources, and the fluxes of element depositions. The results pinpointed Cu and Sb as the main contaminants and suggested a common origin for these two elements from non-exhaust sources of vehicular traffic, such as brake abrasion. Most study sites were, however, found to be subjected to low or moderate environmental contamination, and the lowest contamination corresponded to the main green areas, confirming the important protective role of urban forests against air pollution. Ranges of estimated mean annual element deposition rates in the study area were similar or lower than those reported for other urban areas.

Dissolution and recrystallization in modern shelf carbonates: evidence from pore water and solid phase chemistry

1993 ◽  
Vol 344 (1670) ◽  
pp. 27-36 ◽  
Keyword(s):  
Organic Matter ◽  
Pore Water ◽  
Solid Phase ◽  
Chemical Exchange ◽  
Isotope Composition ◽  
Geochemical Data ◽  
Carbonate Sediments ◽  
Pore Waters ◽  
Carbonate Minerals ◽  
Carbonate Production

We present an overview of geochemical data from pore waters and solid phases that clarify earliest diagenetic processes affecting modern, shallow marine carbonate sediments. Acids produced by organic matter decomposition react rapidly with metastable carbonate minerals in pore waters to produce extensive syndepositional dissolution and recrystallization. Stoichiometric relations among pore water solutes suggest that dissolution is related to oxidation of H 2 S which can accumulate in these low-Fe sediments. Sulphide oxidation likely occurs by enhanced diffusion of O 2 mediated by sulphide-oxidizing bacteria which colonize oxic/anoxic interfaces invaginating these intensely bioturbated sediments. Buffering of pore water stable isotopic compositions towards values of bulk sediment and rapid 45 Ca exchange rates during sediment incubations demonstrate that carbonate recrystallization is a significant process. Comparison of average biogenic carbonate production rates with estimated rates of dissolution and recrystallization suggests that over half the gross production is dissolved and/or recrystallized. Thus isotopic and elemental composition of carbonate minerals can experience significant alteration during earliest burial driven by chemical exchange among carbonate minerals and decomposing organic matter. Temporal shifts in palaeo-ocean carbon isotope composition inferred from bulk-rocks may be seriously compromised by facies-dependent differences in dissolution and recrystallization rates.

scholarly journals Iron and Carbon Isotope Constraints on the Formation Pathway of Iron-Rich Carbonates within the Dagushan Iron Formation, North China Craton

Minerals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 94
Author(s):  
Xiaoxue Tong ◽  
Kaarel Mänd ◽  
Yuhao Li ◽  
Lianchang Zhang ◽  
Zidong Peng ◽  
...  
Keyword(s):  
Iron Reduction ◽  
Isotope Composition ◽  
Iron Formation ◽  
Banded Iron Formations ◽  
Organic C ◽  
Formation Pathway ◽  
Wide Range ◽  
Dissimilatory Iron Reduction ◽  
O Isotope ◽  
Iron Formations

Banded iron formations (BIFs) are enigmatic chemical sedimentary rocks that chronicle the geochemical and microbial cycling of iron and carbon in the Precambrian. However, the formation pathways of Fe carbonate, namely siderite, remain disputed. Here, we provide photomicrographs, Fe, C and O isotope of siderite, and organic C isotope of the whole rock from the ~2.52 Ga Dagushan BIF in the Anshan area, China, to discuss the origin of siderite. There are small magnetite grains that occur as inclusions within siderite, suggesting a diagenetic origin of the siderite. Moreover, the siderites have a wide range of iron isotope compositions (δ56FeSd) from −0.180‰ to +0.463‰, and a relatively negative C isotope composition (δ13CSd = −6.20‰ to −1.57‰). These results are compatible with the reduction of an Fe(III)-oxyhydroxide precursor to dissolved Fe(II) through microbial dissimilatory iron reduction (DIR) during early diagenesis. Partial reduction of the precursor and possible mixing with seawater Fe(II) could explain the presence of siderite with negative δ56Fe, while sustained reaction of residual Fe(III)-oxyhydroxide could have produced siderite with positive δ56Fe values. Bicarbonate derived from both DIR and seawater may have provided a C source for siderite formation. Our results suggest that microbial respiration played an important role in the formation of siderite in the late Archean Dagushan BIF.

scholarly journals Interstellar and interplanetary solids in the laboratory

2015 ◽  
Vol 11 (A29B) ◽  
pp. 416-419 ◽  
Author(s):  
Emmanuel Dartois ◽  
Ivan Alata ◽  
Cécile Engrand ◽  
Rosario Brunetto ◽  
Jean Duprat ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Environmental Parameters ◽  
Interstellar Matter ◽  
Additional Information ◽  
Set Constraints ◽  
Physico Chemical ◽  
Space Environments ◽  
Chemical Conditions ◽  
Extraterrestrial Material ◽  
Shed Light

AbstractThe composition of interstellar matter is driven by environmental parameters and results from extreme interstellar medium physico-chemical conditions. Astrochemists must rely on remote observations to monitor and analyze the interstellar solids composition. They bring additional information from the study of analogues produced in the laboratory, placed in simulated space environments. Planetologists and cosmochemists access and spectroscopically examine collected extraterrestrial material in the laboratory. Diffuse interstellar medium and molecular clouds observations set constraints on the composition of organic solids that can then be compared with collected extraterrestrial materials analyses, to shed light on their possible links.

scholarly journals Assessment of diversity and physico-chemical parameters of cyanobacteria, diatoms and other algal species in the paddy fields of Belagavi district, Karnataka

2020 ◽  
Vol 7 (3) ◽  
pp. 378-382
Author(s):  
Santoshkumar Jayagoudar ◽  
Pradeep Bhat ◽  
Ankita Magdum ◽  
Duradundi Sakreppagol ◽  
Laxmi Murgod ◽  
...  
Keyword(s):  
Algal Species ◽  
Soil Samples ◽  
Chemical Parameters ◽  
Range Estimation ◽  
The North ◽  
Physico Chemical ◽  
Water And Soil Samples ◽  
Study Sites ◽  
Good Range

Algae are the diverse group of organisms in the soil and aquatic environment. The role of them in soil fertility enhancement has been extensively studied worldwide. Belagavi is a tropical agricultural belt in the North Karnataka region with highly fertile soil. Water and soil samples were collected randomly from the paddy field of 15–20 well-distributed spots in 4 selected locations viz Kusumali, Jamboti, Kinaye and Piranwadi. The identification revealed the presence of 94 species and 71 genera in the investigated sites. Among all, 62 species belonged to Bacillariophyceae, 14 species to Chlorophyceae, 10 species to Cyanophyceae, 3 to Xanthophyceae, followed by Trebouxiophyceae and Zygnematophyceae (2 species each) and one species of Ulvophyceae. The maximum number of 62 species was recorded from Kusamali, followed by 49 species in Kinaye, 44 in Jamboti and 35 in Piranwadi. The month of February had the highest number of species (61), decreased to 45 in March, 42 in April and 37 in May. Among the physicochemical parameters analysed for the soil samples, it was found that the pH of the soil is slightly acidic in all the study sites ranged between 5.03–5.85. Further, the electrical conductivity (EC) varied from 0.27–0.345 dS/m, found to be in a good range. Estimation of available micro and macronutrients of soil were measured, and it was found to be at low to moderate levels. The present study indicates the extensive distribution of different classes of algae in the rice fields of four study locations in Belagavi.

Jilin Zircon – A New Natural Reference Material for Microbeam U-Pb Geochronology and Hf-O Isotopic Analysis

2021 ◽  
Author(s):  
Tao Luo ◽  
Qiuli Li ◽  
Xiaoxiao Ling ◽  
Yang Li ◽  
Chuan Yang ◽  
...  
Keyword(s):  
Reference Material ◽  
Isotope Composition ◽  
Isotopic Analysis ◽  
The Matrix ◽  
O Isotope

Zircon U-Pb geochronology and Hf-O isotope composition can provide important information on geological events. The matrix-matched reference material is routinely used to yield accurate and precise zircon U-Pb ages and...

scholarly journals Technical note: Lithium isotopes in dolostone as a palaeo-environmental proxy – an experimental approach

2019 ◽  
Vol 15 (2) ◽  
pp. 635-646 ◽  
Author(s):  
Holly L. Taylor ◽  
Isaac J. Kell Duivestein ◽  
Juraj Farkas ◽  
Martin Dietzel ◽  
Anthony Dosseto
Keyword(s):  
Isotope Fractionation ◽  
Isotope Composition ◽  
Relative Proportion ◽  
Significant Proportion ◽  
Technical Note ◽  
Fractionation Factor ◽  
Calcium Carbonates ◽  
Marine Carbonates ◽  
Li Isotope ◽  
Environmental Proxy

Abstract. Lithium (Li) isotopes in marine carbonates have considerable potential as a proxy to constrain past changes in silicate weathering fluxes and improve our understanding of Earth's climate. To date the majority of Li isotope studies on marine carbonates have focussed on calcium carbonates. The determination of the Li isotope fractionation between dolomite and a dolomitizing fluid would allow us to extend investigations to deep times (i.e. Precambrian) when dolostones were the most abundant marine carbonate archives. Dolostones often contain a significant proportion of detrital silicate material, which dominates the Li budget; thus, pretreatment needs to be designed so that only the isotope composition of the carbonate-associated Li is measured. This study aims to serve two main goals: (1) to determine the Li isotope fractionation between Ca–Mg carbonates and solution, and (2) to develop a method for leaching the carbonate-associated Li out of dolostone while not affecting the Li contained within the detrital portion of the rock. We synthesized Ca–Mg carbonates at high temperatures (150 to 220 ∘C) and measured the Li isotope composition (δ7Li) of the precipitated solids and their respective reactive solutions. The relationship of the Li isotope fractionation factor with temperature was obtained: 103ln⁡αprec-sol=-(2.56±0.27)106(1)/T2+(5.8±1.3) Competitive nucleation and growth between dolomite and magnesite were observed during the experiments; however, there was no notable effect of their relative proportion on the apparent Li isotope fractionation. We found that Li isotope fractionation between the precipitated solid and solution is higher for Ca–Mg carbonates than for Ca carbonates. If the temperature of a precipitating solution is known or can be estimated independently, the above equation could be used in conjunction with the Li isotope composition of dolostones to derive the composition of the solution and hence make inferences about the past Li cycle. In addition, we also conducted leaching experiments on a Neoproterozoic dolostone and a Holocene coral. Results show that leaching with 0.05 M hydrochloric acid (HCl) or 0.5 % acetic acid (HAc) at room temperature for 60 min releases Li from the carbonate fraction without a significant contribution of Li from the siliciclastic detrital component. These experimental and analytical developments provide a basis for the use of Li isotopes in dolostones as a palaeo-environmental proxy, which will contribute to further advance our understanding of the evolution of Earth's surface environments.

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