气候变化领域集成服务门户(CCPortal): Coupled Re-Os and U-Pb geochronology of the Tonian Chuar Group, Grand Canyon

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DOI	10.1130/B31768.1
	Coupled Re-Os and U-Pb geochronology of the Tonian Chuar Group, Grand Canyon
	Rooney A.D.; Austermann J.; Smith E.F.; Li Y.; Selby D.; Dehler C.M.; Schmitz M.D.; Karlstrom K.E.; Macdonald F.A.
发表日期	2018
ISSN	167606
起始页码	1085
结束页码	1098
卷号	130 期号:2021-07-08
英文摘要	Well-preserved strata of the late Tonian Chuar Group exposed in the Grand Canyon host fossil evidence for the development of eukaryotic predation, the presence of unique biomarkers, and large changes in C, S, and Mo isotope chemostratigraphy. Despite the importance of this critical succession, few radioisotopic age constraints are available to place these records into a global context. Here, we couple high-precision U-Pb chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) on zircon crystals with the rhenium-osmium (Re-Os) sedimentary and sulfide geochronometer to refine the temporal framework of this pivotal interval of Earth history. Zircons recovered from a tuff within the uppermost Walcott Member of the Kwagunt Formation yield a weighted mean 206Pb-238U age of 729.0 ± 0.9 Ma (mean square of weighted deviates [MSWD] = 0.86), differing significantly from the previous air-abrasion upper-intercept age of 742 ± 6 Ma on zircons from this same horizon. Organic-rich carbonates from the Carbon Canyon Member of the Galeros Formation yield a model 1 Re-Os age of 757.0 ± 6.8 Ma (MSWD = 0.47, n = 8), and an initial Os isotope (187Os/188Os [Osi]) composition of 1.13 ± 0.02. The radiogenic Osi value from this horizon suggests that the basin was restricted from the open ocean during de- position of the Carbon Canyon Member, in agreement with sedimentological and stratigraphic data. The Re-Os geochronology of marcasite (FeS2) nodules from the Awatubi Member of the Kwagunt Formation yield a model 1 age of 751.0 ± 7.6 Ma (MSWD = 0.37, n = 5), with an Osi of 0.44 ± 0.01. This Re-Os date is interpreted to constrain the growth of the marcasite nodules in the Awatubi Member during deposition. The formation of sulfides and the less radiogenic Osi value are consistent with an influx of sulfate-laden seawater to the basin during deposition of the Kwagunt Formation. Attempts to apply the Re-Os geochronometer to the Walcott and Tanner Members of the Chuar Group failed to yield meaningful ages, despite elevated Re enrichments ( > 20 ng/g). The Re-Os data from these units yielded negative Osi values, which suggest disturbance to the Re-Os system. The low Os abundances (typically < 100 pg/g) relative to the amount expected based on the elevated Re abundances suggest leaching of Os due to oxidative weathering on geologically recent time scales. Finally, the Carbon Canyon Member provides a useful case study for quantifying how input uncertainties in the Re-Os geochronometer propagate into the resulting age uncertainty, and we discuss the protocols that will yield the best improvement in age precision for future studies. The U-Pb and Re-Os geochronology presented here illustrates the power of coupling these systems and the importance of recent improvements in both methods. Our analysis suggests that for our data, the most efficient way of reducing uncertainties in the presented Re-Os dates is through improved precision of measured Os values. © 2018 The Authors.
语种	英语
来源期刊	Bulletin of the Geological Society of America
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/185017
作者单位	Department of Geology and Geophysics, Yale University, New Haven, CT 06511, United States; Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, United States; Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Cambridge, CB3 0EZ, United Kingdom; Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, United States; Department of Earth Sciences, Durham University, Durham, DH1 3LE, United Kingdom; Department of Geology, Utah State University, Logan, UT 84322, United States; Department of Geosciences, Boise State University, Boise, ID 83725, United States; Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, United States
推荐引用方式 GB/T 7714	Rooney A.D.,Austermann J.,Smith E.F.,et al. Coupled Re-Os and U-Pb geochronology of the Tonian Chuar Group, Grand Canyon[J],2018,130(2021-07-08).
APA	Rooney A.D..,Austermann J..,Smith E.F..,Li Y..,Selby D..,...&Macdonald F.A..(2018).Coupled Re-Os and U-Pb geochronology of the Tonian Chuar Group, Grand Canyon.Bulletin of the Geological Society of America,130(2021-07-08).
MLA	Rooney A.D.,et al."Coupled Re-Os and U-Pb geochronology of the Tonian Chuar Group, Grand Canyon".Bulletin of the Geological Society of America 130.2021-07-08(2018).