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Palaeoproterozoic evaporites in Fennoscandia: implications for seawater sulphate, the rise of atmospheric oxygen and local amplification of the δ13C excursion

This paper addresses global oxygenation and establishment of a marine sulphate reservoir in the Palaeoproterozoic. We report syn‐depositional, marine, anhydrite‐containing pseudomorphs after Ca‐sulphates as widespread throughout the Tulomozero Formation in the SE Fennoscandian Shield, implying that surface waters were oxidized and a large SO marine reservoir was developed as early as 2100 Ma. The Ca‐sulphates and associated magnesite and halite precipitated syn‐depositionally from oxidized, evolved and modified seawater in coastal playa, sabkha and intertidal flat settings. 87Sr/86Sr and δ13C of associated 13C‐rich stromatolitic dolostones were environmentally controlled with the highest ratios occurring in playa and sabkha carbonates. The results imply that the Palaeoproterozoic δ13Ccarb excursion was amplified by 8‰ by local environmental factors and calls into question many observations of putative δ13C global signals reported previously from similar Palaeoproterozoic, evaporitic, dolostones. The local environmental amplification can explain a large regional and intercontinental δ13C discrepancy observed in synchronous carbonates.