7.3 The Palaeoproterozoic Perturbation of the Global Carbon Cycle: The Lomagundi-Jatuli Isotopic Event

Abstract

On Earth, carbon cycles through the land, ocean, atmosphere, living and dead biomass and the planet's interior. The global carbon cycle can be divided into the tectonically driven geological cycle and the biological/physicochemical cycles. The former operates over millions of years, whereas the latter operate over much shorter time scales (days to thousands of years). Within the geological cycle, atmospheric carbon dioxide concentration is controlled by the balance between weathering, biological drawdown, size of sedimentary reservoir, subduction, metamorphism and volcanism over time periods of hundreds of millions of years

Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere

“…This event is known as the Lomagundi carbon isotope excursion, with δ 13 C values reaching upwards of 12 per mil. The event lasted well over 100 million years, with a termination estimated at between about 2,110 Ma and 2,080 Ma and no later than 2,060 Ma (10,14). This excursion represents the largest positive carbon-isotope excursion in Earth history.…”

“…Some have argued that the GOE occurred as a direct result of cyanobacterial evolution (5) whereas others have assumed that cyanobacteria evolved well before the GOE and have looked for causes involving changes in the redox balance of the Earth surface (6)(7)(8)(9). In any event, beginning after the GOE, and sometime between 2,300 and 2,230 Ma, there was a large positive excursion in the 13 C of marine inorganic carbon that was apparently global in nature (10)(11)(12)(13). This event is known as the Lomagundi carbon isotope excursion, with δ 13 C values reaching upwards of 12 per mil.…”

Graphite from Palaeoproterozoic enhanced carbon burial, and its metallogenic legacy

“…This event was closely followed by the deposition of extensive black (carbon-rich) shales, the Shunga Event˜2.0 Ga, on several continents (Condie et al 2001;Strauss et al 2013;Martin et al 2015). The abundance of carbon may reflect intense weathering of the continents following the Great Oxidation Event, and high productivity in the nutrient-rich oceans (Melezhik et al 2013). The identification of this episode as the peak of black shale sedimentation in the Precambrian, from 2.0 to 1.85 Ga (Condie et al 2001), is based on data from Australia (57 %), North America (37 %) and Russia (6 %).…”

Characteristic disruptions of an excitable carbon cycle

“…1 could reflect the transient addition of 2 pulses of isotopically light carbon originating, for example, from the respiration of a previously unreactive reservoir of organic carbon (10,11). Such disruptions have also been interpreted as geochemical responses to other sources of environmental change, including variations in Earth's orbital parameters (12); dissociation of methane hydrate (13); bolide impacts (14); biogeochemical innovations (15,16); and changes in chemical weathering (17), organic carbon burial (18), and volcanic emissions (19). These interpretations typically treat the marine carbon cycle as a passive recorder of an externally imposed stress.…”