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

• 成果类型: Article
• 署名作者: Gan, Tian; Tian, Meng; Wang, Xi-Kai; Wang, Shijie; Liu, Xiao-Ming; Jiang, Ganqing; Gill, Benjamin C.; Nolan, Morrison; Kaufman, Alan J.; Luo, Taiyi; Xiao, Shuhai
• 署名单位: Chinese Academy of Sciences; Institute of Geochemistry, CAS; Virginia Polytechnic Institute & State University; University System of Maryland; University of Maryland College Park; Chinese Academy of Sciences; University of Chinese Academy of Sciences, CAS; University of Bern; University of Munich; University of North Carolina; University of North Carolina Chapel Hill; Nevada System of Higher Education (NSHE); University of Nevada Las Vegas; University System of Ohio; Denison University; University System of Maryland; University of Maryland College Park; Chinese Academy of Sciences; Institute of Geochemistry, CAS
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11320
• DOI: 10.1073/pnas.2407419121
• 发表日期: 2024-11-12
• 关键词: cap dolostones; carbonate; constraints; temperature; EVOLUTION; seawater; li; fractionation; stratigraphy; circulation

摘要

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 S 7 Li trend with distance from the shoreline, consistent with the variable mixing of a meltwater plume with high S 7 Li (due to incongruent silicate weathering on the continent) and hypersaline seawater with low S 7 Li (due to synglacial distillation). The evolution of low S 7 Li of synglacial seawater, as opposed to the modern oceans with high S 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 S 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 S 7 Li data are consistent with the plumeworld hypothesis, considerably reduced chemical weathering on the continent during the Marinoan snowball Earth, and enhanced reverse weathering on the seafloor of Precambrian oceans.