Factors contributing to high δ13C values in Cryogenian limestones of western Mongolia

Shields, Graham, Brasier, Martin D., Stille, Peter C., and Dorjnamjaa, Dorj-iin (2002) Factors contributing to high δ13C values in Cryogenian limestones of western Mongolia. Earth and Planetary Science Letters, 196 (3-4). pp. 99-111.

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Abstract

A geochemical study of Cryogenian (late Neoproterozoic) limestones from western Mongolia is presented, including δ¹³C (carbonate and kerogen), δ¹⁸O, ⁸⁷Sr/⁸⁶Sr and rare earth element data. Carbon isotope compositions confirm the existence of anomalously high δ¹³C in Cryogenian seawater with δ¹³C(carb)>+10‰. Positive δ¹³C excursions are explained conventionally by elevated rates of organic carbon burial. However, four additional factors appear likely to have contributed to δ¹³C excursions during the Cryogenian: (1) increased δ¹³C of carbon input (δi) due to the exposure and weathering of carbonate platforms during sea-level falls, (2) increased carbon isotopic discrimination between carbonates and organic carbon (Δδ¹³C) due to microbial reworking of primary organic matter, (3) locally elevated δ¹³C in restricted basins and (4) enhanced vertical gradients in seawater δ¹³C due to redox stratification. All four factors may have contributed to similar positive δ¹³C excursions at other times, and may help to explain the almost ubiquitous association of eustatic regression, and cooling, with high δ¹³C during the late Neoproterozoic and early Palaeozoic.

Item ID: 27422
Item Type: Article (Research - C1)
ISSN: 1385-013X
Keywords: carbon composites, stable isotopes, creium, anomalies, neoproterozoic, Mongolia, limestone
Date Deposited: 04 Jun 2013 01:48
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040299 Geochemistry not elsewhere classified @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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