Testing Urey's carbonate-silicate cycle using the calcium isotopic composition of sedimentary carbonates

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doi: 10.1016/j.epsl.2017.09.033
Author(s): Blattler, Clara L.; Higgins, John A.
Author Affiliation(s): Primary:
Princeton University, Department of Geosciences, Princeton, NJ, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.479, p.241-251. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Includes appendix. 53 refs.; illus.
Summary: Carbonate minerals constitute a major component of the sedimentary geological record and an archive of a fraction of the carbon and calcium cycled through the Earth's surface reservoirs for over three billion years. For calcium, carbonate minerals constitute the ultimate sink for almost all calcium liberated during continental and submarine weathering of silicate minerals. This study presents >500 stable isotope ratios of calcium in Precambrian carbonate sediments, both limestones and dolomites, in an attempt to characterize the isotope mass balance of the sedimentary carbonate reservoir through time. The mean of the dataset is indistinguishable from estimates of the calcium isotope ratio of bulk silicate Earth, consistent with the Urey cycle being the dominant mechanism exchanging calcium among surface reservoirs. The variability in bulk sediment calcium isotope ratios within each geological unit does not reflect changes in the global calcium cycle, but rather highlights the importance of local mineralogical and/or diagenetic effects in the carbonate record. This dataset demonstrates the potential for calcium isotope ratios to help assess these local effects, such as the former presence of aragonite, even in rocks with a history of neomorphism and recrystallization. Additionally, 29 calcium isotope measurements are presented from ODP (Ocean Drilling Program) Site 801 that contribute to the characterization of altered oceanic crust as an additional sink for calcium, and whose distinct isotopic signature places a limit on the importance of this subduction flux over Earth history.
Year of Publication: 2017
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 06 Petrology, Sedimentary; Alkaline earth metals; Aragonite; Ca-44/Ca-40; Calcium; Carbon cycle; Carbonate rocks; Carbonate sediments; Carbonates; Crust; Diagenesis; Geochemical cycle; Isotope ratios; Isotopes; Marine environment; Mass balance; Mass spectra; Metals; North Pacific; Northwest Pacific; ODP Site 801; Ocean Drilling Program; Oceanic crust; Pacific Ocean; Pigafetta Basin; Precambrian; Preservation; Sedimentary rocks; Sediments; Silicates; Sinks; Spectra; Stable isotopes; Steady-state processes; Submarine environment; Weathering; West Pacific
Coordinates: N183831 N183835 E1562136 E1562134
Record ID: 2018012570
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands