Kolosjoki Sedimentary Formation: A record in the aftermath of the Paleoproterozoic global positive δ13C excursion in sedimentary carbonates

- We investigated sedimentary carbonates from the Kolosjoki Sedimentary Formation.
- The Kolosjoki formation postdates the Lomagundi-Jatuli isotope excursion.
- We found a δ13C trend from − 2 to 3‰ in the Kolosjoki succession.
- The results provide evidence for a minimum in the δ13C curve at 2060-1970 Ma.

The Kolosjoki Sedimentary Formation of the Pechenga Greenstone Belt, north eastern Fennoscandia, records the aftermath of the Paleoproterozoic global positive δ13C excursion in sedimentary carbonates (the Lomagundi-Jatuli isotope excursion). The goals of this research were to provide detailed new data on the δ13C trend in the Kolosjoki Sedimentary Formation and generate a secular δ13C curve for the time period immediately succeeding the Lomagundi-Jatuli isotope excursion. For these purposes, sedimentary carbonate samples from two new drillcores representing the Kolosjoki Sedimentary Formation were collected. In total 88 whole-rock samples and 67 micro-drilled subsamples (ca. 1-3 mg) were analyzed for the isotope composition of C and O, the whole-rock elemental abundances, and for the composition of the acid-soluble fraction. The Kolosjoki carbonate rocks are dolostone or calcitic dolostone (Mg/Ca = 0.50-0.67) with minor limestone (Mg/Ca = 0.04-0.06). Only weak correlation was observed between the Mn/Sr ratios and the δ13C and δ18O values, and the carbonate samples have likely retained their near-primary δ13C values. The sedimentary carbonate rocks show first low δ13C values at − 2 to − 1‰ and then a subtle, upward increasing δ13C trend from ca. 1 to 3‰. The increasing δ13C trend is interpreted to record a recovery from a δ13C minimum following the Lomagundi-Jatuli isotope excursion.