On the Lomagundi-Jatuli carbon isotopic event: The evidence from the Kalix Greenstone Belt, Sweden

We report a significant new database on the carbon and oxygen isotopic analyses (233 whole-rock, and 43 microcored samples) obtained from sedimentary dolostones in the Kalix Greenstone Belt from the Fennoscandian Shield of Sweden. This characterises the second half of the prominent Palaeoproterozoic Lomagundi-Jatuli positive carbon-isotope excursion. Within a 600 m-thick succession of alternating volcanic, volcaniclastic, siliciclastic and dolomitic rocks from greenschist–epidote-amphibolite metamorphic facies, the least altered dolostone samples show a gentle oscillation between +2‰ and +4‰ throughout stratigraphy with a second-order positive excursion from +4‰ through +8‰, and gradually back again to +4‰ in the c. 150 m-thick unit in the middle and upper parts of the succession. This second-order excursion is superimposed on the general relatively rapid δ13C decline at the second half of the Lomagundi-Jatuli isotopic event and coincides with the transition from a marine-influenced rift to a passive margin setting. If the excursion is global, it would reveal internal fine structure of the Lomagundi-Jatuli isotopic excursion; if not, basinal local factors are the main players. Lithostratigraphic and C-isotope correlation between Kalix and neighbouring Peräpohja Schist Belt successions, 40-km-apart, suggest an incomplete geological record in both successions despite the absence of obvious non-depositional unconformities.