Lithium isotope evidence for a plumeworld ocean in the aftermath of the Marinoan snowball Earth

作者：Tian Gan, Meng Tian, Xi-Kai Wang, Shijie Wang, Xiaoming Liu, Ganqing Jiang, Benjamin C. Gill, Morrison Nolan, Alan J. Kaufman, Taiyi Luo, Shuhai Xiao · 发表于：Proceedings of the National Academy of Sciences · 年份：2024 · DOI：10.1073/pnas.2407419121 · 被引用次数：6 · 研究领域：Paleontology and Stratigraphy of Fossils、Geology and Paleoclimatology Research、Geochemistry and Elemental Analysis

The snowball Earth hypothesis predicts that continental chemical weathering diminished substantially during, but rebounded strongly after, the Marinoan ice age some 635 Mya. Defrosting the planet would result in a plume of fresh glacial meltwater with a different chemical composition from underlying hypersaline seawater, generating both vertical and lateral salinity gradients. Here, we test the plumeworld hypothesis using lithium isotope compositions in the Ediacaran Doushantuo cap dolostone that accumulated in the aftermath of the Marinoan snowball Earth along a proximal–distal (nearshore–offshore) transect in South China. Our data show an overall decreasing δ 7 Li trend with distance from the shoreline, consistent with the variable mixing of a meltwater plume with high δ 7 Li (due to incongruent silicate weathering on the continent) and hypersaline seawater with low δ 7 Li (due to synglacial distillation). The evolution of low δ 7 Li of synglacial seawater, as opposed to the modern oceans with high δ 7 Li, was likely driven by weak continental chemical weathering coupled with strong reverse weathering on the seafloor underneath silica-rich oceans. The spatial pattern of δ 7 Li is also consistent with the development and then collapse of the meltwater plume that occurred at the time scale of cap dolostone accumulation. Therefore, the δ 7 Li data are consistent with the plumeworld hypothesis, considerably reduced chemical weathering on the continent during the Marinoan snowba...