Authigenic clay mineral evidence for restricted, evaporitic conditions during the emergence of the Ediacaran Doushantuo Biota

The Ediacaran Period witnessed major environmental change and an expansion of eukaryotic life following the Marinoan glaciation. The Doushantuo Formation of south China has furnished much of our understanding of Earth System and biosphere evolution during this period, but its depositional setting–marine or non-marine–is still debated. Here we conduct mineralogical, petrographic and geochemical analyses of samples from the lower Doushantuo Formation in order to determine the origin of saponite clay minerals which are abundant in this interval. We find that the morphology and distribution of the saponite clays suggest they are of pre-compaction, authigenic origin. We infer that the lower Doushantuo sediments were deposited in a restricted, mildly evaporitic lagoonal basin, offering additional constraints on the environmental setting into which metazoan life emerged. Further, our findings confirm that Ediacaran seawater favored reverse weathering, with marine clay formation likely representing an important sink for various elements during the Precambrian.