Isotopic standards for carbon and oxygen and correction factors for mass-spectrometric analysis of carbon dioxide
Abstract
Seventy-four mass spectrometric analyses have been made on eight isotopic standards for carbon and oxygen. The standards reported on are the National Bureau of Standards limestone, water, and graphite reference samples, the Solenhofen standard used by Niee for absolute measurements, and the carbonate standards used by the Stockholm, Basel, Wellington and Chicago laboratories. The basic measurements are reported as δ values relative to the Chicago PDB standard and as absolute isotope ratios. The absolute ratios are based on new figures for Nier's standard, derived from a reevaluation of his data and new measurements on atmospheric oxygen.
The correction factors for instrumental effects and for the nature of the mass spectra have been studied. Simple but precise equations for the mass spectra effects have been derived, which give the correction factors as functions of the measured differences between sample and standard. The oxygen isotopic composition of carbon dioxide produced by combustion of carbon has been studied and the derived correction factors for carbon measurements were checked experimentally by varying the oxygen-18 content of carbon dioxide.
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Improved accuracy over a wider range.
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Easy use and implementation of the scheme.
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Convenient uncertainty calculation in accordance with international standards.
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Setting new standards: Multiphasic analysis of microplastic mineralization by fungi
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Carbon and oxygen isotope microanalysis of calcite in the Permian Kupferschiefer system, Saale subbasin, eastern Germany
2023, Chemical GeologyThe Kupferschiefer district in Central Europe contains some of the world's highest-grade sediment-hosted stratiform Cu (SSC) deposits. In the Saale subbasin (eastern Germany), high-grade sulfides formed via replacement of calcite cement in the continental sandstones of the uppermost Rotliegend (S1), the overlying organic-rich marine mudstones of the Kupferschiefer (T1) and the Zechstein Limestone (Ca1) units. The spatial distribution of the calcite cement, therefore, had a fundamental role to play in the Cu mineralizing system. In this study, we investigate the origin of the calcite cement (and crosscutting calcite veins) using detailed petrography (cathodoluminescence, CL; scanning electron microscopy, SEM), major element chemistry (electron probe microanalyzer, EPMA), and secondary ion mass spectrometry (SIMS) microanalyses of δ13C and δ18O values in drill core samples (n = 47) from the Saale subbasin. The calcite cement in the S1, T1 and Ca1 has a similar CL response and major element chemistry, suggestive of a common origin. Overlapping δ13C and δ18O values in calcite cement in samples from the S1 and T1 in the Sangerhausen and Wallendorf drill cores also suggest that the calcite cement was derived from fluids of similar composition. The low δ13C values of calcite cement in samples from the S1 (−13‰ to 4.3‰, VPDB) and T1 (−10‰ to 0.7‰) indicates carbonate alkalinity was sourced mainly from seawater-derived fluids and the oxidation of organic matter. The wide range of δ18O values in the calcite cement in the S1 (∼18‰ to 31‰, VSMOW) and T1 (∼ 22‰ to 31‰) samples suggest they are derived from pore fluids with a chemical composition influenced by early diagenetic alteration of detrital clasts, mainly dissolution of volcanic rock fragments, with minor contributions from the influx of meteoric waters and evaporated seawater. The negative δ13C values (down to −15‰) in calcite veins from the T1 and Ca1 indicate sources of carbonate alkalinity derived from organic matter degradation. Our data demonstrate that no isotopic hydrothermal alteration haloes can be inferred from the δ13C and δ18O values in calcite cement associated with the high-grade sulfide mineralization. The lack of systematic isotopic variability in the calcite cement likely indicates the mineralizing fluid flux or temperature was not sufficient to overprint the background sources of isotopic variability, which may help to explain the modest size of SSC deposits in this part of the Kupferschiefer district.
Symbiotic N nutrition, carbon accumulation, and water-use efficiency in species of the genus Aspalathus native to the Cape fynbos, South Africa
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Present address: Scripps Institution of Oceanography, University of California, La Jolla, California.