The Paleoproterozoic Otish and Mistassini basins of Quebec, Canada: A record of Superia supercraton breakup and the end of the Lomagundi-Jatuli carbon isotope excursion

The Otish Supergroup and Mistassini Group of north-central Quebec are two weakly metamorphosed sedimentary successions deposited during the middle Paleoproterozoic along the modern-day eastern margin of the Archean Superior craton. This study presents new uranium-lead (U-Pb) detrital zircon and shale rhenium-osmium (Re-Os) geochronological data for these two successions, as well as δ¹³C_carb data from sedimentary carbonate rocks, which comprise the first such data for the Otish Supergroup. New geochronological data presented here demonstrate that the Mistassini Group was deposited between 2121 Ma and 1825 Ma and postdates the Otish Supergroup by at least ∼20 m.y. The δ¹³C_carb data from the Otish Supergroup are strongly enriched, typically +7‰ to +12‰, and therefore consistent with deposition during the Lomagundi-Jatuli carbon isotope excursion (LJE), which is generally considered to have occurred during ca. 2220−2060 Ma. Within the basal ∼200 m of the Mistassini Group, δ¹³C_carb values reach almost +8‰, before shifting to near 0‰ in the overlying ∼1800 m of strata, which indicates that it records the termination of the LJE. The Re-Os depositional age of 1825 ± 9 Ma for mudstones of the Kallio Formation, the uppermost formation in the Mistassini Group, provides a minimum constraint for deposition in the basin. Cumulatively, the new radiometric ages and stable isotope ratio data provide a basis for a new tectonostratigraphic reconstruction that closely links the Mistassini and Otish basins to the evolution of the Labrador Trough and other basins along the eastern and southern margins of the Superior craton.