The Ancient Anoxic Biosphere Was Not As We Know It

8.1 The Great Oxidation Event

“…Thus, the oxygenation of the atmosphere-ocean system presumably provided additional terminal electron acceptors such as sulphate, which would result in a more diverse carbon cycling in the sedimentary realm. Melezhik et al (1999Melezhik et al ( , 2005 and Fallick et al (2008Fallick et al ( , 2011 presented data supporting this hypothesis in the form of carbon isotopic compositions of diagenetic carbonates of Archaean and Proterozoic age. Interestingly, pre-Palaeoproterozoic diagenetic carbonates, with the exception of those found in banded iron formations, have d…”

7.6 Enhanced Accumulation of Organic Matter: The Shunga Event

“…Although regional/local amplifications have been addressed (e.g. Melezhik et al 1999b), the presence of positive to even strongly positive carbonate carbon isotope values in coeval sedimentary successions worldwide, being the prime characteristic of the Lomagundi-Jatuli Event, have been viewed as an expression of the enhanced deposition of organic matter (but see Hayes and Waldbauer 2006, or Fallick et al 2008 for alternative interpretations).…”

“…Melezhik et al 1999b). Following isotope mass balance consideration, the presence of strongly positive carbonate carbon isotope values suggests the enhanced deposition of organic matter (but see Hayes and Waldbauer 2006, and Fallick et al 2008 for alternative interpretations; see also Chap. 7.3).…”

“…Second, the carbonate carbon isotopic record at c. 2.0 Ga displays a substantial number of d 13 C carb values around 0 ‰, but also includes 13 C-enriched as well as strongly 13 C-depleted carbon isotope data as low as À18 ‰ (for compilations, see Shields and Veizer 2002;Fallick et al 2008;Prokoph et al 2009). d 13 C carb values around 0 ‰ suggest an operation of the global carbon cycle comparable to most parts of Earth history, i.e.…”

7.7 The Earliest Phosphorites: Radical Change in the Phosphorus Cycle During the Palaeoproterozoic

“…It appears that the first phosphorites coincide in time (c. 2000 Ma) with the abundant formation of 13 C-depleted, diagenetic carbonate concretions in siliciclastic rocks. The appearance of carbonate concretions was interpreted to track the onset of effective recycling of organic matter in the sedimentary column as the biospheric response to increased oxygen concentrations (Fallick et al 2008). However, the relative importance of individual factors triggering the earliest phosphogenic episode remains poorly understood and awaits further studies.…”