Geochemistry of a 1.2 Ga carbonate-evaporite succession, northern Baffin and Bylot Islands: implications for
A 4 ‰ positive shift in the carbon isotopic composition of the oceans, recorded globally in marine carbonate rocks at 1.3 Ga, suggests a significant change in Mesoproterozoic carbon cycling. Enhanced burial fluxes of organic carbon, relative to inorganic carbon, implied by this isotopic shift may ha...
| Main Authors: | , , , |
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| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
2000
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| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.501.851 http://web.eps.utk.edu/~faculty/kah/pdf/Kahetal(2001).pdf |
| Summary: | A 4 ‰ positive shift in the carbon isotopic composition of the oceans, recorded globally in marine carbonate rocks at 1.3 Ga, suggests a significant change in Mesoproterozoic carbon cycling. Enhanced burial fluxes of organic carbon, relative to inorganic carbon, implied by this isotopic shift may have resulted in increased oxygenation of the Earth’s biosphere, as has been suggested for similar Paleoproterozoic and Neoproterozoic carbon isotope events. This hypothesized Mesoproterozoic oxygenation event may be recorded in the geologic record by the appearance of the oldest preserved, laterally extensive, bedded marine CaSO4 evaporites in the 1.2 Ga Grenville and Bylot supergroups. Speculation that the appearance of extensively preserved marine gypsum and/or anhydrite reflects increased biospheric oxygenation has been challenged, however, by the hypothesis that CaSO4 precipitation prior to the Mesoproterozoic may have been inhibited by significantly higher marine carbonate saturation, which would have facilitated carbonate precipitation and effectively limited Ca2+ availability during seawater evaporation (Grotzinger, J.P., 1989. Controls on Carbonate Platform and Basin Development, vol. 44, SEPM, Tulsa, OK, pp. 79–106), regardless of O2 levels. The 1.2 Ga Society Cliffs Formation (Bylot Supergroup, northern Baffin Island) consists of 720 m of peritidal carbonates, evaporites, and minor siliciclastic rocks. Evaporites occur predominantly in the lowermost 300 m of the Society Cliffs Formation, where gypsum beds (1–250 cm thick) constitute up to 15 % of the |
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