The Lomagundi-Jatuli Event and Earth’s oxygenation

The Palaeoproterozoic Lomagundi-Jatuli Event (LJE) is the largest positive carbonate C-isotope ( δ13Ccarb) excursion in Earth history. Conventional thinking is that it represents a perturbation of the global C cycle between c. 2.3–2.1 Ga linked directly to the postulated Great Oxidation Event. Here we show that the LJE worldwide is, in fact, entirely facies (i.e. palaeoenvironment) dependent. During the LJE, the C-isotope composition of open and deeper marine settings remained undisturbed, with a mean d13Ccarb value of 1.5‰, whereas nearshore marine and coastal-evaporitic settings have means of 6.2‰ and 8.1‰, respectively. This finding refutes conventional thinking and obliges complete re-evaluation of concepts using the LJE as a means of assessing oxygenation of the atmosphere.