Cryptic sulfur cycling during the formation of giant gypsum deposits

Salt giants are large-scale, basin-wide deposits formed sporadically in the geological past, from early Paleozoic to late Cenozoic. Their role as sinks for seawater dissolved ions is well known, however biogeochemical conditions that accompany salt giant formation and their effects on carbon cycling remain poorly constrained. Here we show massive gypsum of Mediterranean – youngest Earth a particularly dynamic environment controlled by orbitally-driven climate oscillations at precessional scale. Using multiple sulfur isotopes combined with steady-state cycle model, that, prior precipitation, more than 80% its constituting sulfate was first microbially reduced into sulfide, possibly stored elemental sulfur, then almost completely reoxidized back sulfate. This “cryptic” contemporaneous precipitation implies both negligible net consumption sulfide production, despite significant benthic flux organic remineralized through microbial reduction. known evidence cryptic past.