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Heterogeneity in the Ediacaran-Cambrian coastal oceans; a sulphur isotope perspective

Ying Lin, Nanping Wu, Li Da and Ling Hongfei
Heterogeneity in the Ediacaran-Cambrian coastal oceans; a sulphur isotope perspective
Geological Magazine (July 2020) 157 (7): 1112-1120


Multiple sulphur isotope compositions of sedimentary pyrites across the Ediacaran-Cambrian (Ed-C) transition and into the early Cambrian from the Xiaotan section, Yunnan, South China, are presented to explore the evolution of the sulphur cycle. The values of delta (super 34) S (sub py) range from 13.5 ppm to 35.8 ppm, and the values of Delta (super 33) S (sub py) range from -0.044 ppm to 0.063 ppm. The first-order observation of highly positive delta (super 34) S (sub py) is consistent with sulphur isotope records from other sedimentary successions (with various degrees of enrichment in (super 34) S), reflecting a common feature in cycling of sulphur among ocean basins. The positive values suggest that pyrite was formed in a depositional setting with limiting availability of sulphate that suppressed the expression of microbial fractionations. The first-order observation of a 10-million-year period of negative Delta (super 33) S (sub py) beginning around the Ed-C boundary likely reflects changes in isotopic compositions of sulphur influx to the oceans. Such changes are suggested to be linked to a pulse of preferred weathering of sulphides (with negative Delta (super 33) S) relative to sulphate, which may reflect enhanced exposure of pyrites in continental margins due to reorganization of continents at this time. Both delta (super 34) S (sub py) and Delta (super 33) S (sub py) data imply low seawater sulphate levels, and possibly heterogeneity in sulphate concentrations in the world's coastal oceans. The predictions about sulphur isotope signatures of evolved seawater (with highly positive delta (super 34) S and negative Delta (super 33) S) at the Xiaotan section are testable with future measurements of carbonate-associated sulphate (CAS), a proxy of ancient oceanic sulphate that carries information about the operation of sulphur cycling on a global scale.

ISSN: 0016-7568
EISSN: 1469-5081
Coden: GEMGA4
Serial Title: Geological Magazine
Serial Volume: 157
Serial Issue: 7
Title: Heterogeneity in the Ediacaran-Cambrian coastal oceans; a sulphur isotope perspective
Affiliation: University of California, Riverside, Department of Earth and Planetary Sciences, Riverside, CA, United States
Pages: 1112-1120
Published: 202007
Text Language: English
Publisher: Cambridge University Press, London, United Kingdom
References: 74
Accession Number: 2020-063288
Categories: Isotope geochemistryStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. col., 1 table, geol. sketch map
N28°07'17" - N28°07'17", E103°28'16" - E103°28'16"
Secondary Affiliation: University of Maryland, USA, United StatesNanjing University, CHN, China
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, Copyright, Cambridge University Press. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202018
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