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DOI	10.1016/j.epsl.2021.117002
	The Ca and Mg isotope record of the Cryogenian Trezona carbon isotope excursion
	Ahm A.-S.C.; Bjerrum C.J.; Hoffman P.F.; Macdonald F.A.; Maloof A.C.; Rose C.V.; Strauss J.V.; Higgins J.A.
发表日期	2021
ISSN	0012821X
卷号	568
英文摘要	The Trezona carbon isotope excursion is recorded on five different continents in platform carbonates deposited prior to the end-Cryogenian Marinoan glaciation (>635 Ma) and represents a change in carbon isotope values of 16–18‰. Based on the spatial and temporal reproducibility, the excursion previously has been interpreted as tracking the carbon isotopic composition of dissolved inorganic carbon in the global ocean before the descent into a snowball Earth. However, in modern restricted shallow marine and freshwater settings, carbon isotope values have a similarly large range, which is mostly independent from open ocean chemistry and instead reflects local processes. In this study, we combine calcium, magnesium, and strontium isotope geochemistry with a numerical model of carbonate diagenesis to disentangle the degree to which the Trezona excursion reflects changes in global seawater chemistry versus local shallow-water platform environments. Our analysis demonstrates that the most extreme carbon isotope values (∼-10‰ versus +10‰) are preserved in former platform aragonite that was neomorphosed to calcite during sediment-buffered conditions and record the primary carbon isotope composition of platform-top surface waters. In contrast, the downturn and recovery of the Trezona excursion are recorded in carbonates that were altered during early fluid-buffered diagenesis and commonly are dolomitized. We also find that the nadir of the Trezona excursion is associated with a fractional increase in siliciclastic sediments, whereas the recovery from the excursion correlates with a relative increase in carbonate. This relationship suggests that the extreme negative isotopic shift in platform aragonite occurred in concert with periods of increased input of siliciclastic sediments, changes in water depth, and possibly nutrients to platform environments. Although the process for generating extremely negative carbon isotope values in Neoproterozoic platform carbonates remains enigmatic, we speculate that these excursions reflect kinetic isotope effects associated with CO2 invasion in platform waters during periods of intense primary productivity. © 2021 The Author(s)
关键词	Ca and Mg isotopes carbon cycle diagenesis Snowball Earth Trezona excursion
英文关键词	Calcite; Calcium; Carbon; Carbonate minerals; Glacial geology; Magnesium; Sedimentology; Sediments; Ca and mg isotope; Carbon cycles; Carbon isotope excursions; Carbon isotopes; Cryogenian; Isotope values; Mg isotopes; Siliciclastic sediments; Snowball Earth; Trezona excursion; Isotopes; carbon cycle; carbon isotope; cryogenic fluid; diagenesis; glaciation; global ocean; inorganic carbon; isotopic composition; magnesium; numerical model; Proterozoic
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/203016
作者单位	Princeton University, Guyot Hall, Princeton, NJ 08540, United States; University of Copenhagen, Øster Voldgade 10, Copenhagen K, 1350, Denmark; University of Victoria, School of Earth and Ocean SciencesBC, Canada; University of California, Santa Barbara, Department of Earth ScienceCA 93106, United States; University of St Andrews, Irvine Building, St. Andrews, United Kingdom; Dartmouth College, Fairchild Hall, Hanover, NH 03755, United States
推荐引用方式 GB/T 7714	Ahm A.-S.C.,Bjerrum C.J.,Hoffman P.F.,et al. The Ca and Mg isotope record of the Cryogenian Trezona carbon isotope excursion[J],2021,568.
APA	Ahm A.-S.C..,Bjerrum C.J..,Hoffman P.F..,Macdonald F.A..,Maloof A.C..,...&Higgins J.A..(2021).The Ca and Mg isotope record of the Cryogenian Trezona carbon isotope excursion.Earth and Planetary Science Letters,568.
MLA	Ahm A.-S.C.,et al."The Ca and Mg isotope record of the Cryogenian Trezona carbon isotope excursion".Earth and Planetary Science Letters 568(2021).