The grandest of them all: the Lomagundi-Jatuli Event and Earth's oxygenation

The Paleoproterozoic Lomagundi-Jatuli Event (LJE) is generally considered the largest, in both amplitude and duration, positive carbonate C-isotope (delta C-13(carb)) excursion in Earth history. Conventional thinking is that it represents a global perturbation of the carbon cycle between 2.3-2.1 Ga linked directly with, and in part causing, the postulated rise in atmospheric oxygen during the Great Oxidation Event. In addition to new high-resolution delta C-13(carb) measurements from LJE-bearing successions of NW Russia, we compiled 14 943 delta C-13(carb) values obtained from marine carbonate rocks 3.0-1.0 Ga in age and from selected Phanerozoic time intervals as a comparator of the LJE. Those data integrated with sedimentology show that, contra to consensus, the delta C-13(carb) trend of the LJE is facies (i.e. palaeoenvironment) dependent. Throughout the LJE interval, the C-isotope composition of open and deeper marine settings maintained a mean delta C-13(carb) value of +1.5 +/- 2.4 parts per thousand, comparable to those settings for most of Earth history. In contrast, the C-13-rich values that are the hallmark of the LJE are limited largely to nearshore-marine and coastal-evaporitic settings with mean delta C-13(carb) values of +6.2 +/- 2.0 parts per thousand and +8.1 +/- 3.8 parts per thousand, respectively. Our findings confirm that changes in delta C-13(carb) are linked directly to facies changes and archive contemporaneous dissolved inorganic carbon pools having variable C-isotopic compositions in laterally adjacent depositional settings. The implications are that the LJE cannot be construed a priori as representative of the global carbon cycle or a planetary-scale disturbance to that cycle, nor as direct evidence for oxygenation of the ocean-atmosphere system. This requires rethinking models relying on those concepts and framing new ideas in the search for understanding the genesis of the grandest of all positive C-isotope excursions, its timing and its hypothesized linkage to oxygenation of the atmosphere.

Automated summary

The study suggests that the C-13 isotope trend of the LJE is facies-dependent rather than representative of the global carbon cycle. While open and deeper marine environments maintained stable carbon isotope values, nearshore and evaporitic environments showed higher C-13 values. Changes in C-13 values are linked to facies changes and may be related to local carbon pools.