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 SO42- 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. Sr-87/Sr-86 and delta(13)C of associated C-13-rich stromatolitic dolostones were environmentally controlled with the highest ratios occurring in playa and sabkha carbonates. The results imply that the Palaeoproterozoic delta(13)C(carb) excursion was amplified by 8% by local environmental factors and calls into question many observations of putative delta(13)C global signals reported previously from similar Palaeoproterozoic, evaporitic, dolostones. The local environmental amplification can explain a large regional and intercontinental delta(13)C discrepancy observed in synchronous carbonates.