Distribution features of carbon isotopes in carbonates on the example of the Sartiu Formation (Lower Carboniferous, Vorkuta Uplift)
Research subject. The carbon and oxygen isotope composition of rock carbonates and brachiopod shells in the section of the upper part of the Sartiu Formation (Mississippian, Vorkuta uplift). Aim . Comparative evaluation of isotopic signal preservation in brachiopod shells and host rock on the exampl...
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| Vydané v: | Litosfera (Ekaterinburg. Online) Ročník 25; číslo 3; s. 398 - 418 |
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| Hlavní autori: | , , , , |
| Médium: | Journal Article |
| Jazyk: | English Russian |
| Vydavateľské údaje: |
15.07.2025
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| ISSN: | 1681-9004, 2500-302X |
| On-line prístup: | Získať plný text |
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| Shrnutí: | Research subject. The carbon and oxygen isotope composition of rock carbonates and brachiopod shells in the section of the upper part of the Sartiu Formation (Mississippian, Vorkuta uplift).
Aim . Comparative evaluation of isotopic signal preservation in brachiopod shells and host rock on the example of strongly secondary altered sediments.
Methods. Data on foraminifera, conodonts, and brachiopods formed the stratigraphic framework. Carbon and oxygen isotope analyses of carbonates of brachiopod shells and host rock, accompanied by screening tests, were determined for 76 samples from 35 levels within the upper part of the Serpukhovian Stage. Data on carbonate recrystallisation, organic carbon content, carbon-oxygen isotope ratio, cathodoluminescence, and taxonomic affiliation of brachiopods were used for screening.
Results. The data on carbon isotope composition showed significant differences in isotopic signals in brachiopod shells and in the host rock. The lower part of the section (approximately 4.3 m) is characterized by a heavying of the carbon isotopic composition of the shell material from 2.0 to 4.1‰. Higher up the section (next 2.5 m), a sharp increase in δ13C up to 7.3‰ is observed (sample with Davidsonina carbonaria ) followed by a decrease to 3.4‰ and then a scatter of values from 1.2 to 6‰ in the uppermost part. At the same time, the carbon isotope composition of limestones shows rather stable values along the entire section (from –0.2 to 2.6‰, mean value 1.0‰), showing a slight negative trend towards the upper part. According to the screening tests, all limestone samples show a highly altered signal by secondary processes; however, brachiopod shell carbonate is assumed to have a near-primary isotopic composition. At the same time, the isotopic composition of brachiopod shells strongly depends on taxonomic affiliation. In representatives of the Davidsonina genus, a significant (by 4–6‰) heavying of the carbon isotopic composition was noted. The average δ18O values of limestones are 21.3‰ SMOW (corresponding to –9.3‰ PDB) and brachiopod shells 22.2‰ (corresponding to –8.4‰ PDB), which rules out the primary nature of oxygen isotopic composition.
Conclusions. The studied material showed good preservation of the isotopic signal in brachiopod shells even in the case of significant recrystallisation of the host carbonates. The significant vital effect characteristic of representatives of the Davidsonina genus makes it difficult to use isotopic data obtained from these brachiopod shells for the purposes of isotopic stratigraphy. For correct isotopestratigraphic interpretation of variations in carbon isotope composition in sections, taxonomically homogeneous samples within at least one genus should be studied. |
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| ISSN: | 1681-9004 2500-302X |
| DOI: | 10.24930/2500-302X-2025-25-3-398-418 |