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Platinum-group elements (PGE) and rhenium in marine sediments across the Cretaceous–Tertiary boundary: Constraints on Re-PGE transport in the marine environment

Lee, Cin-Ty Aeolus and Wasserburg, Gerald J. and Kyte, Frank T. (2003) Platinum-group elements (PGE) and rhenium in marine sediments across the Cretaceous–Tertiary boundary: Constraints on Re-PGE transport in the marine environment. Geochimica et Cosmochimica Acta, 67 (4). pp. 655-670. ISSN 0016-7037. doi:10.1016/S0016-7037(02)01135-3.

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The nature of Re–platinum-group element (PGE; Pt, Pd, Ir, Os, Ru) transport in the marine environment was investigated by means of marine sediments at and across the Cretaceous–Tertiary boundary (KTB) at two hemipelagic sites in Europe and two pelagic sites in the North and South Pacific. A traverse across the KTB in the South Pacific pelagic clay core found elevated levels of Re, Pt, Ir, Os, and Ru, each of which is approximately symmetrically distributed over a distance of ∼1.8 m across the KTB. The Re-PGE abundance patterns are fractionated from chondritic relative abundances: Ru, Pt, Pd, and Re contents are slightly subchondritic relative to Ir, and Os is depleted by ∼95% relative to chondritic Ir proportions. A similar depletion in Os (∼90%) was found in a sample of the pelagic KTB in the North Pacific, but it is enriched in Ru, Pt, Pd, and Re relative to Ir. The two hemipelagic KTB clays have near-chondritic abundance patterns. The ∼1.8-m-wide Re-PGE peak in the pelagic South Pacific section cannot be reconciled with the fallout of a single impactor, indicating that postdepositional redistribution has occurred. The elemental profiles appear to fit diffusion profiles, although bioturbation could have also played a role. If diffusion had occurred over ∼65 Ma, the effective diffusivities are ∼10^(−13) cm^2/s, much smaller than that of soluble cations in pore waters (∼10^(−6) cm^2/s). The coupling of Re and the PGEs during redistribution indicates that postdepositional processes did not significantly fractionate their relative abundances. If redistribution was caused by diffusion, then the effective diffusivities are the same. Fractionation of Os from Ir during the KTB interval must therefore have occurred during aqueous transport in the marine environment. Distinctly subchondritic Os/Ir ratios throughout the Cenozoic in the South Pacific core further suggest that fractionation of Os from Ir in the marine environment is a general process throughout geologic time because most of the inputs of Os and Ir into the ocean have Os/Ir ratios ≥1. Mass balance calculations show that Os and Re burial fluxes in pelagic sediments account for only a small fraction of the riverine Os (<10%) and Re (<0.1%) inputs into the oceans. In contrast, burial of Ir in pelagic sediments is similar to the riverine Ir input, indicating that pelagic sediments are a much larger repository for Ir than for Os and Re. If all of the missing Os and Re is assumed to reside in anoxic sediments in oceanic margins, the calculated burial fluxes in anoxic sediments are similar to observed burial fluxes. However, putting all of the missing Os and Re into estuarine sediments would require high concentrations to balance the riverine input and would also fail to explain the depletion of Os at pelagic KTB sites, where at most ∼25% of the K-T impactor’s Os could have passed through estuaries. If Os is preferentially sequestered in anoxic marine environments, it follows that the Os/Ir ratio of pelagic sediments should be sensitive to changes in the rates of anoxic sediment deposition. There is thus a clear fractionation of Os and Re from Ir in precipitation out of sea water in pelagic sections. Accordingly, it is inferred here that Re and Os are removed from sea water in anoxic marine depositional regimes.

Item Type:Article
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Wasserburg, Gerald J.0000-0002-7957-8029
Additional Information:© 2003 Elsevier Science Ltd. Received April 22, 2002; accepted in revised form August 7, 2002. Diane McDaniel, Thomas Meisel, associate editor R. Walker, and an anonymous reviewer are thanked for reviews. Discussions with James Chen, Jerome Gaillardet, Damien LeMarchand, Graham Pearson, and Bernhard Peucker-Ehrenbrink are appreciated. Samples from DSDP 465 and DSDP 596 were supplied by Ocean Drilling Program, which is curated with support from the National Science Foundation. Samples SK10 and SM503 were collected and supplied by J. Smit. This study was supported by DOE DF FG03- 88ER13851. This is Caltech contribution 8894 (1096). Associate editor: R. Walker
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-88ER13851
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Caltech Division of Geological and Planetary Sciences 8894
Lunatic Asylum Lab 1096
Issue or Number:4
Record Number:CaltechAUTHORS:20131118-153534558
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Official Citation:Cin-Ty Aeolus Lee, Gerald J. Wasserburg, Frank T. Kyte, Platinum-group elements (PGE) and rhenium in marine sediments across the Cretaceous–Tertiary boundary: constraints on Re-PGE transport in the marine environment, Geochimica et Cosmochimica Acta, Volume 67, Issue 4, 15 February 2003, Pages 655-670, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42540
Deposited By: Ruth Sustaita
Deposited On:18 Nov 2013 23:48
Last Modified:10 Nov 2021 16:24

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