Fig. 6.

Calculated δ¹⁸O compositions of the diagenetic fluids (δ¹⁸O_fluid) versus paired T_∆47 data for Doushantuo dolomite. Recrystallization environments (colored text: early or late diagenetic or anchi-metamorphic) except for those modern environments in blue texts are either closed (i.e., rock-buffered) or open (i.e., fluid-buffered). Reference isotopic compositions for carbonates and coexisting diagenetic fluids equilibrated over a range of geological conditions were adopted from ref. 36 but updated to the δ¹⁸O compositions of dolomite. All originally calculated δ¹⁸O_fluid values were corrected to modern seawater δ¹⁸O by adding +6.5‰ as modeled by ref. 38. The initial T_∆47 values from modeling are based on a solid-state reordering model assuming a hydrothermal event with a peak heating of 270 °C for 2,000 y. See Methods for further explanation of calculations and Results and Discussion for detailed interpretations.