The terminal Permian extinction event ended the dominance of calcite-secreting benthic faunas that had prevailed during the Paleozoic. Most of those calcite secretors (especially brachiopods and corals) were replaced during the Early and Middle Triassic by aragonite-secreting faunas (especially bivalves and scleractinian corals). Geochemical evidence suggests that a unique combination of elevated sulfate concentrations, elevated temperatures, and possibly elevated Mg/Ca ratios characterized Early and Middle Triassic seawater. These Triassic geochemical conditions may have favored evolution of the aragonitic faunas that arose in the aftermath of the Permian extinctions and that have subsequently dominated the Mesozoic and Cenozoic.

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