DOI: 10.1016/j.epsl.2021.117002
论文题名: The Ca and Mg isotope record of the Cryogenian Trezona carbon isotope excursion
作者: 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.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2021
卷: 568 语种: 英语
中文关键词: 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
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) Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165394
Appears in Collections: 气候变化与战略
There are no files associated with this item.
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
Recommended Citation:
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]. Earth and Planetary Science Letters,2021-01-01,568