Wide but not ubiquitous distribution of glendonite in the Doushantuo Formation, South China: Implications for Ediacaran climate

Wang, Zhou, Chen, Can, Wang, Jiasheng, Suess, Erwin, Chen, Xiaohong, Ma, Xiaochen, Wang, Guangzhe and Xiao, Shuhai (2020) Wide but not ubiquitous distribution of glendonite in the Doushantuo Formation, South China: Implications for Ediacaran climate Precambrian Research, 338 (Article number 105586). DOI 10.1016/j.precamres.2019.105586.

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• Glendonites are widely distributed in Ediacaran Doushantuo Formation of South China.
• Host strata are characterized by positive δ13C and record excursion EP1.
• Calcitic glendonites are characterized by variable and extremely negative δ13C.
• Doushantuo glendonites represent a cooling event prior to EN3 or Shuram excursion.
• Low T°C, phosphate, and anoxic conditions facilitated glendonite/ikaite formation.

Glendonites are pseudomorphs of syndepositional or early authigenic ikaite (CaCO3·6H2O) that often forms at near-freezing temperatures. Silicified glendonite has been reported from inner-shelf deposits of the lower Ediacaran Doushantuo Formation at a single stratigraphic section in South China, where they are stratigraphically associated with the positive δ13C excursion EP1 but predate the negative δ13C excursion EN3 (=Shuram excursion), indicating a period of cool climate somewhere between ~609 Ma and ~551 Ma. This interpretation predicts a wider geographic distribution of Ediacaran glendonites in equivalent strata in the Yangtze Block of South China. To test this prediction, we conducted a regional survey of Doushantuo Formation and found that, although glendonites are not universally present, they occur in expected stratigraphic intervals and in association with EP1 at two new sections representing inner-shelf and intrashelf basin facies. The wide but not ubiquitous distribution of Doushantuo glendonites indicates that ikaite precipitation and glendonite formation was controlled by both regional climatic and local geochemical factors. Glendonites at the new localities are stellate clusters pseudomorphed by calcite spar and sometimes are rimmed with silica. The calcite spar is characterized by highly variable and mostly negative δ13C values as low as −37‰, indicating that diagenetic transformation of precursor ikaite to calcitic glendonite may be related to anaerobic oxidation of organic matter or methane in sediment. The new data suggest an early Ediacaran cold period prior to EN3 or the Shuram excursion and facilitation of glendonite/ikaite formation by both climatic and local geochemical conditions such as redox conditions and phosphate concentrations.

Document Type: Article
Keywords: Carbon isotopes, Climate cooling, Doushantuo Formation, Ediacaran Period, Glendonite, South China
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
Refereed: Yes
DOI etc.: 10.1016/j.precamres.2019.105586
ISSN: 0301-9268
Date Deposited: 07 Jan 2020 12:54
Last Modified: 07 Jan 2020 15:46
URI: http://eprints.uni-kiel.de/id/eprint/48607

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