Neoproterozoic cap-dolostone deposition in stratified glacial meltwater plume

Chao Liu*, Zhengrong Wang, Timothy D. Raub, Francis A. Macdonald, David A. D. Evans

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Citations (Scopus)

Abstract

Neoproterozoic cap carbonates host distinctive geochemical and sedimentological features that reflect prevailing conditions in the aftermath of Snowball Earth. Interpretation of these features has remained contentious, with hypotheses hinging upon timescale and synchronicity of deposition, and whether or not geochemical signatures of cap carbonates represent those of a well-mixed ocean. Here we present new high-resolution Sr and Mg isotope results from basal Ediacaran cap dolostones in South Australia and Mongolia. Least-altered Sr and Mg isotope compositions of carbonates are identified through a novel incremental leaching technique that monitors the purity of a carbonate sample and the effects of diagenesis. These data can be explained by the formation of these cap dolostones involving two chemically distinct solutions, a glacial meltwater plume enriched in radiogenic Sr, and a saline ocean residue with relatively lower 87Sr/86Sr ratios. Model simulations suggest that these water bodies remained dynamically stratified during part of cap-dolostone deposition, most likely lasting for ∼8 thousand years. Our results can potentially reconcile previous conflicts between timescales estimated from physical mixing models and paleomagnetic constraints. Geochemical data from cap carbonates used to interpret the nature of Snowball Earth and its aftermath should be recast in terms of a chemically distinct meltwater plume.
Original languageEnglish
Pages (from-to)22-32
Number of pages11
JournalEarth and Planetary Science Letters
Volume404
Early online date7 Aug 2014
DOIs
Publication statusPublished - 15 Oct 2014

Keywords

  • Cap dolostones
  • Sr isotopes
  • Mg isotopes
  • Snowball Earth
  • Plumeworld
  • SNOWBALL EARTH
  • SOUTH-AUSTRALIA
  • ISOTOPIC COMPOSITION
  • DOLOMITE PRECIPITATION
  • DOUSHANTUO FORMATION
  • MICROBIAL MEDIATION
  • EDIACARAN SYSTEM
  • DEEP-OCEAN
  • CARBONATE
  • CONSTRAINTS

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