Kolosjoki Sedimentary Formation: A record in the aftermath of the Paleoproterozoic global positive delta 13C excursion in sedimentary carbonates

• Published in: Chemical geology 2013-12, Vol.362, p.165-180
• Main Authors: Salminen, Paula E, Karhu, Juha A, Melezhik, Victor A
• Format: Article
• Language: English
• Subjects: Belts; Carbonates; Formations; Isotopes; Limestone; Magnesium; Rocks; Trends
• ISSN: 0009-2541
• DOI: 10.1016/j.chemgeo.2013.10.018

The Kolosjoki Sedimentary Formation of the Pechenga Greenstone Belt, north eastern Fennoscandia, records the aftermath of the Paleoproterozoic global positive delta 13C excursion in sedimentary carbonates (the Lomagundi-Jatuli isotope excursion). The goals of this research were to provide detailed new data on the delta 13C trend in the Kolosjoki Sedimentary Formation and generate a secular delta 13C 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. 1-3mg) 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 delta 13C and delta 18O values, and the carbonate samples have likely retained their near-primary delta 13C values. The sedimentary carbonate rocks show first low delta 13C values at -2 to -1ppt and then a subtle, upward increasing delta 13C trend from ca. 1 to 3ppt. The increasing delta 13C trend is interpreted to record a recovery from a delta 13C minimum following the Lomagundi-Jatuli isotope excursion.