Hydrothermal dedolomitisation of carbonate rocks of the Paleoproterozoic Zaonega Formation, NW Russia — Implications for the preservation of primary C isotope signals

T. Kreitsmann, M. Külaviir, A. Lepland, K. Paiste, P. Paiste, A. R. Prave, H. Sepp, A.E. Romashkin, D.V. Rychanchik, K. Kirsimäe

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

The Paleoproterozoic Zaonega Formation in Karelia, NW Russia, has played a key role in understanding the environmental conditions postdating the Great Oxidation and Lomagundi-Jatuli Events. Its carbonate- and organic-rich rocks (shungite) define the postulated Shunga Event representing an accumulation of very organic-rich sediments at c. 2 Ga and are central in ideas about changing ocean-atmosphere composition in the wake of those worldwide biogeochemical phenomena. Our work focussed on a key interval of carbonate rocks in the upper part of the Formation to: (i) obtain new high-resolution carbon, oxygen and strontium isotope data complemented by detailed petrography and mineralogical characterisation and (ii) expand upon previous studies by using our data to constrain geochemical modelling and show in greater detail how magmatic hydrothermal fluids induced dedolomitisation and altered geochemical signals. Our findings show that the δ13Ccarb of calcite-rich intervals are the most altered, with values between −16.9 to 0.6‰, whereas the dolomite-dominated parts retain the best-preserved (i.e. most original) values. Those define a trend of steadily increasing δ13Ccarb, from −6 to +0.5‰, which we interpret as a return to normal marine conditions and carbonate‑carbon values following the Lomagundi-Jatuli Event.
Original languageEnglish
Pages (from-to)43-57
Number of pages15
JournalChemical Geology
Volume512
Early online date3 Mar 2019
DOIs
Publication statusPublished - 5 May 2019

Keywords

  • Dedolomitisation
  • Carbonate geochemistry
  • Carbonate stable isotopes
  • Shunga Event

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