Neoproterozoic sulfur-isotope variation in Australia and global implications

P. Gorjan, J. J. Veevers, M. R. Walter*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    91 Citations (Scopus)

    Abstract

    Seven sulfur-isotope stages are apparent in Australian Neoproterozoic sections. (1) From 840 Ma to the Sturtian glaciation (700 Ma) δ34S(sulfate) varied little (+19 to +17.5‰) and δ34S(sulfide) ranged from -20 to +23‰. (2) The Sturtian glaciation was followed by (3) a rise in δ34S(sulfide) to an average of +30‰ (seen also in China, Namibia and Canada) and in δ34S(sulfate) at least to +26‰ and possibly to +45‰. The sharp rise in δ34S of all sulfur fractions (sulfate, sulfide, and organic) leads us to speculate that sulfide depleted in 34S was deposited on the abyssal plain and that residual sulfate enriched in 34S remained beneath a stagnant, ice-covered ocean during the Sturtian glaciation and was brought to the shallow continental margin during the post-glacial transgression. (4) δ34S(sulfide) and δ34S(sulfate) fall from 640 to 607 Ma (δ34S(sulfate) down to +17‰) probably from oxygen excess (through massive organic carbon burial), which causes weathering of sulfide depleted in 34S continental sulfide and previously deposited sulfide on the abyssal plain. (5) The oxic environment of the Marinoan (605-595 Ma) glaciation minimises sulfate-reduction (unlike the Sturtian) so that δ34S(sulfate) is unvarying. (6) The post-glacial environment has sulfide depleted in 34S (average δ34S(sulfide) < -30‰). Burial of a substantial quantity of organic-carbon causes extensive bacterial reduction of sulfate and a rise in δ34S(sulfate) to a peak of at least +32‰ (7) around the Neoproterozoic-Cambrian boundary and a corresponding rise in δ34S(sulfide), explained by release of methane gas from clathrate and a subsequent heatwave causing ocean stagnation and oxygen depletion. (C) 2000 Elsevier Science B.V. All rights reserved.

    Original languageEnglish
    Pages (from-to)151-179
    Number of pages29
    JournalPrecambrian Research
    Volume100
    Issue number1-3
    DOIs
    Publication statusPublished - Mar 2000

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