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Controls of eustasy and diagenesis on the 238U/235U of carbonates and evolution of the seawater (234U/238U) during the last 1.4 Myr

Published on Dec 1, 2018in Geochimica et Cosmochimica Acta4.26
· DOI :10.1016/j.gca.2018.08.022
F. L. H. Tissot9
Estimated H-index: 9
(U of C: University of Chicago),
Cindy Chen2
Estimated H-index: 2
(U of C: University of Chicago)
+ 5 AuthorsNicolas Dauphas47
Estimated H-index: 47
(U of C: University of Chicago)
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Abstract
Using a leaching protocol designed for the study of U isotopes in recent carbonates, we measured the U isotope composition, both ^(238)U/^(235)U and ^(234)U/^(238)U, of modern and ancient corals (n = 6), a limestone and a dolostone, as well as 43 shallow-water carbonate sediments from the ODP Leg 166 Site 1009 drill core, on the slope of the Bahamas platform. Although bulk corals record the seawater δ^(238)U value within ±0.02‰, differences of up to 0.30‰ in the δ^(238)U of individual leachates suggest a control of the coral structure and a more positive ^(238)U/^(235)U ratio in the centers of calcification. The drill core δ^(238)U data shows that the ^(238)U/^(235)U ratio of shallow-water carbonates is controlled mainly by (1) variations in sea-level through the mixing of different amounts of platform-derived sediments (with δ^(238)U ∼0.50–0.60‰ heavier than seawater) and pelagic sediments (with seawater-like δ^(238)U values), (2) authigenic U enrichment via pore-watercirculation and U reduction both on the platform and down to ∼5 m below the surface (mbsf) after deposition of the sediment, and, to a lesser extent, by (3) early diagenetic processes (i.e., carbonate dissolution and/or recrystallization) during sediment burial. The global effect of these processes leaves the δ^(238)U values of shallow-water carbonates offset relative to that of seawater by Δ_(Carbonates-SW) = +0.24 ± 0.06‰ (95% CI, including all samples). This shift can be used in seawater paleoredox reconstructions based on carbonates deposited on shallow-water platform, shelf and slope environments (i.e., most of the carbonate sedimentary record prior to the Mesozoic) to account for the average effect of carbonate diagenesis. Assuming that the ^(238)U/^(235)U ratio of carbonate platform sediments directly records the seawater ^(238)U/^(235)U ratio would underestimate the extent of ocean-seafloor anoxia by at least a factor 10. The rapid fluctuations in δ^(238)U values due to sea-level changes (i) is a factor that should be considered before interpreting δ^(238)U variations as reflecting changes in oceanic paleoredox conditions and (ii) reinforces the need for statistically meaningful data sets. The δ(^(234)U) data suggest that the (^(234)U/^(238)U) ratio of the seawater has remained within ∼20‰ of the modern seawater value during the last 1–1.4 Myr. Furthermore, we find that small-scale (1–15‰) variations in seawater δ(^(234)U) mirror sea-level changes during the penultimate glacial-interglacial period (∼140 to ∼200 ka), thus confirming the record of lower δ(^(234)U)_(SW) during periods of low sea-level stand and expanding it to at least the last two glacial-interglacial events (i.e., ∼0.23 Ma). Such fluctuations in δ(^(234)U)_(initial) values should be taken into account when screening carbonate sediments U-Th ages on the basis of the initial (^(234)U/^(238)U) ratios of the samples.
  • References (133)
  • Citations (3)
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References133
Newest
Published on Jul 1, 2018in Geochimica et Cosmochimica Acta4.26
Ashleigh v.S. Hood10
Estimated H-index: 10
(Yale University),
Noah J. Planavsky36
Estimated H-index: 36
(Yale University)
+ 1 AuthorsXiangli Wang17
Estimated H-index: 17
(Yale University)
Abstract Metal and metal isotope records in carbonates have the potential to provide novel insights into ancient ocean–atmosphere redox conditions, paleoenvironmental conditions, and biogeochemical cycling. However, trace element geochemical signatures in carbonates can record either diagenetic or depositional signatures. Here we explore the variability in uranium isotopes, trace metal and rare earth element + yttrium (REY) concentrations in carbonate successions that have undergone several comm...
Published on Jul 1, 2018in Geology5.01
Guangyi Wei1
Estimated H-index: 1
(Yale University),
Noah J. Planavsky36
Estimated H-index: 36
(Yale University)
+ 4 AuthorsLINGHongfei28
Estimated H-index: 28
(NU: Nanjing University)
Rick Bartlett1
Estimated H-index: 1
(LSU: Louisiana State University),
Maya Elrick19
Estimated H-index: 19
(UNM: University of New Mexico)
+ 3 AuthorsYemane Asmerom35
Estimated H-index: 35
(UNM: University of New Mexico)
Widespread marine anoxia is hypothesized as the trigger for the second pulse of the Late Ordovician (Hirnantian) mass extinction based on lithologic and geochemical proxies that record local bottom waters or porewaters. We test the anoxia hypothesis using δ 238 U values of marine limestones as a global seawater redox proxy. The δ 238 U trends at Anticosti Island, Canada, document an abrupt late Hirnantian ∼0.3‰ negative shift continuing through the early Silurian indicating more reducing seawate...
Published on Jun 1, 2018in Science Advances
Feifei Zhang6
Estimated H-index: 6
(ASU: Arizona State University),
Shuhai Xiao51
Estimated H-index: 51
(VT: Virginia Tech)
+ 6 AuthorsAriel D. Anbar56
Estimated H-index: 56
(ASU: Arizona State University)
Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).
Published on Apr 1, 2018in Science Advances
Feifei Zhang6
Estimated H-index: 6
(ASU: Arizona State University),
Stephen J. Romaniello13
Estimated H-index: 13
(ASU: Arizona State University)
+ 7 AuthorsAriel D. Anbar56
Estimated H-index: 56
(ASU: Arizona State University)
Explaining the ~5-million-year delay in marine biotic recovery following the latest Permian mass extinction, the largest biotic crisis of the Phanerozoic, is a fundamental challenge for both geological and biological sciences. Ocean redox perturbations may have played a critical role in this delayed recovery. However, the lack of quantitative constraints on the details of Early Triassic oceanic anoxia (for example, time, duration, and extent) leaves the links between oceanic conditions and the d...
Matthew O Clarkson8
Estimated H-index: 8
(University of Otago),
Claudine H. Stirling29
Estimated H-index: 29
(University of Otago)
+ 6 AuthorsTimothy M. Lenton53
Estimated H-index: 53
(University of Exeter)
Oceanic Anoxic Event 2 (OAE 2), occurring ∼94 million years ago, was one of the most extreme carbon cycle and climatic perturbations of the Phanerozoic Eon. It was typified by a rapid rise in atmospheric CO2, global warming, and marine anoxia, leading to the widespread devastation of marine ecosystems. However, the precise timing and extent to which oceanic anoxic conditions expanded during OAE 2 remains unresolved. We present a record of global ocean redox changes during OAE 2 using a combined ...
Published on Mar 1, 2018in Geochimica et Cosmochimica Acta4.26
Peter M. Chutcharavan2
Estimated H-index: 2
(UF: University of Florida),
Andrea Dutton15
Estimated H-index: 15
(UF: University of Florida),
Michael J. Ellwood29
Estimated H-index: 29
(ANU: Australian National University)
Abstract U-series dating of corals is a crucial tool for generating absolute chronologies of Late Quaternary sea-level change and calibrating the radiocarbon timescale. Unfortunately, coralline aragonite is susceptible to post-depositional alteration of its primary geochemistry. One screening technique used to identify unaltered corals relies on the back-calculation of initial 234 U/ 238 U activity (δ 234 U i ) at the time of coral growth and implicitly assumes that seawater δ 234 U has remained...
Published on Mar 1, 2018in Geochimica et Cosmochimica Acta4.26
Carli A. Arendt5
Estimated H-index: 5
(UM: University of Michigan),
Sarah M. Aciego14
Estimated H-index: 14
(UW: University of Wyoming)
+ 3 AuthorsEmily I. Stevenson5
Estimated H-index: 5
(University of Cambridge)
Abstract We present the first published uranium-series measurements from modern Greenland Ice Sheet (GrIS) runoff and proximal seawater, and investigate the influence of glacial melt on global seawater δ 234 U over glacial-interglacial (g-ig) timescales. Climate reconstructions based on closed-system uranium-thorium (U/Th) dating of fossil corals assume U chemistry of seawater has remained stable over time despite notable fluctuations in major elemental compositions, concentrations, and isotopic...
Published on Feb 9, 2018in Geology5.01
Feifei Zhang6
Estimated H-index: 6
(ASU: Arizona State University),
Thomas J. Algeo28
Estimated H-index: 28
(UC: University of Cincinnati)
+ 4 AuthorsAriel D. Anbar56
Estimated H-index: 56
(ASU: Arizona State University)
Published on Feb 1, 2018in Geochimica et Cosmochimica Acta4.26
Thai T. Phan5
Estimated H-index: 5
(University of Pittsburgh),
James B. Gardiner2
Estimated H-index: 2
(University of Pittsburgh)
+ 1 AuthorsBrian W. Stewart22
Estimated H-index: 22
(University of Pittsburgh)
Abstract We investigate sediment sources, depositional conditions and diagenetic processes affecting the Middle Devonian Marcellus Shale in the Appalachian Basin, eastern USA, a major target of natural gas exploration. Multiple proxies, including trace metal contents, rare earth elements (REE), the Sm-Nd and Rb-Sr isotope systems, and U isotopes were applied to whole rock digestions and sequentially extracted fractions of the Marcellus shale and adjacent units from two locations in the Appalachi...
Cited By3
Newest
Tais Wittchen Dahl14
Estimated H-index: 14
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James N. Connelly33
Estimated H-index: 33
+ 5 AuthorsMartin Bizzarro33
Estimated H-index: 33
The proliferation of large, motile animals 540 to 520 Ma has been linked to both rising and declining O2 levels on Earth. To explore this conundrum, we reconstruct the global extent of seafloor oxygenation at approximately submillion-year resolution based on uranium isotope compositions of 187 marine carbonates samples from China, Siberia, and Morocco, and simulate O2 levels in the atmosphere and surface oceans using a mass balance model constrained by carbon, sulfur, and strontium isotopes in t...
Published on Sep 1, 2019in Earth and Planetary Science Letters4.64
Geoffrey J. Gilleaudeau6
Estimated H-index: 6
(ASU: Arizona State University),
Stephen J. Romaniello13
Estimated H-index: 13
(ASU: Arizona State University)
+ 9 AuthorsWang Zheng7
Estimated H-index: 7
(ASU: Arizona State University)
Abstract Reconstructing Earth's oxygenation history is key to deciphering environmental controls on early biospheric evolution. During the mid-Proterozoic Eon, low (but potentially variable) atmospheric p O 2 led to highly heterogeneous marine redox conditions, with most studies indicating a relatively shallow depth of oxygen penetration. The relative proportion of oxic, anoxic and iron-rich (ferruginous), and anoxic and sulfide-rich (euxinic) conditions on the global seafloor is difficult to qu...
Published on Sep 1, 2019in Palaeogeography, Palaeoclimatology, Palaeoecology2.62
Guang-Yi Wei3
Estimated H-index: 3
(NU: Nanjing University),
LINGHongfei28
Estimated H-index: 28
(NU: Nanjing University)
+ 6 AuthorsZHUMaoyan32
Estimated H-index: 32
Abstract The emergence and radiation of metazoans have been widely attributed to a progressively more oxidizing surface environment through the Ediacaran–Cambrian transition interval. However, the root causes for atmospheric and oceanic oxygenation are still disputed. Long-term tectonic changes could possibly have led to atmospheric oxygenation but geochemical evidence for this linkage remains elusive. In this study, we analyzed the radiogenic Nd isotopic compositions (eNd) of shallow-marine car...
Kimberly V. Lau6
Estimated H-index: 6
,
Stephen J. Romaniello13
Estimated H-index: 13
,
Feifei Zhang6
Estimated H-index: 6
Published on Oct 1, 2018in Earth-Science Reviews9.53
Feifei Zhang1
Estimated H-index: 1
(Yale University),
Thomas J. Algeo28
Estimated H-index: 28
(UC: University of Cincinnati)
+ 5 AuthorsAriel D. Anbar56
Estimated H-index: 56
Abstract The Smithian-Spathian boundary (SSB) was an interval characterized by a major global carbon cycle perturbation, climatic cooling from a middle/late Smithian boundary hyperthermal condition, and a major setback in the recovery of marine necto-pelagic faunas from the end-Permian mass extinction. Although the SSB has been linked to changes in oceanic redox conditions, key aspects of this redox variation (e.g., duration, extent, and triggering mechanisms) and its relationship to coeval clim...
Published on 2019in Geobiology4.10
Feifei Zhang6
Estimated H-index: 6
,
Shuhai Xiao51
Estimated H-index: 51
(VT: Virginia Tech)
+ 7 AuthorsTimothy M. Lenton53
Estimated H-index: 53
(University of Exeter)
Published on Apr 1, 2019in Geochimica et Cosmochimica Acta4.26
Anne M. Gothmann5
Estimated H-index: 5
(Princeton University),
J.A. Higgins37
Estimated H-index: 37
(Princeton University)
+ 7 AuthorsMichael L. Bender70
Estimated H-index: 70
(Princeton University)
Abstract We measured U/Ca ratios, 4 He concentrations, 234 U/ 238 U, and 238 U/ 235 U in a subset of well-preserved aragonitic scleractinian fossil corals previously described by Gothmann et al. (2015). Comparisons of measured fossil coral He/U ages with the stratigraphic age demonstrate that well-preserved coral aragonite retains most or all of its radiogenic He for 10’s of millions of years. Such samples must be largely or entirely free of alteration, including neomorphism. Measurements of 234...
Published on 2019in Journal of Analytical Atomic Spectrometry3.65
F. L. H. Tissot9
Estimated H-index: 9
,
Mauricio Ibanez-Mejia11
Estimated H-index: 11
+ 4 AuthorsT. Mark Harrison77
Estimated H-index: 77
Owing to the challengingly small amounts of uranium (U) they contain, the isotopic composition (238U/235U) of single zircon grains has never been measured. Leveraging methods we designed for analysis of small sample loads and modern MC-ICPMS instruments, we show that precise (±0.04 to ±0.25 ‰) single-zircon 238U/235U measurements are now possible. We report data for 31 single grains from the Jack Hills conglomerate, and 3 reference zircon localities (FC-1, R33 and Temora). Consistent with the re...
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