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Primary U distribution in scleractinian corals and its implications for U series dating

Robinson, Lauren F. and Adkins, Jess F. and Fernandez, Diego P. and Burnett, Donald S. and Wang, S.-L. and Gagnon, Alexander C. and Krakauer, Nir (2006) Primary U distribution in scleractinian corals and its implications for U series dating. Geochemistry, Geophysics, Geosystems, 7 (5). Q05022. ISSN 1525-2027. http://resolver.caltech.edu/CaltechAUTHORS:ROBggg06

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Abstract

In this study we use microsampling techniques to explore diagenetic processes in carbonates. These processes are important as they can affect the accuracy of U series chronometry. Fission track maps of deep-sea scleractinian corals show a threefold difference between the minimum and maximum [U] in modern corals, which is reduced to a factor of 2 in fossil corals. We use micromilling and MC-ICP-MS to make detailed analyses of the [U] and δ234Uinitial distributions in corals from 218 ka to modern. Within each fossil coral we observe a large range of δ234Uinitial values, with high δ234Uinitial values typically associated with low [U]. A simple model shows that this observation is best explained by preferential movement of alpha-decay produced 234U atoms (alpha-recoil diffusion). Open-system addition of 234U may occur when alpha-recoil diffusion is coupled with a high [U] surface layer, such as organic material. This process can result in large, whole-coral δ234Uinitial elevations with little effect on the final age. The diagenetic pathways that we model are relevant to both shallow-water and deep-sea scleractinian corals since both exhibit primary [U] heterogeneity and may be subject to U addition.


Item Type:Article
Additional Information:Copyright 2006 by the American Geophysical Union. Received 6 September 2005; accepted 10 March 2006; published 24 May 2006 We gratefully acknowledge The Comer Foundation for Abrupt Climate Change and the helpful comments of two anonymous reviewers.
Subject Keywords:uranium; diagenesis; coral; dating; Radiogenic isotope geochemistry; geochronology; isotopic disequilibrium dating; paleoceanography
Record Number:CaltechAUTHORS:ROBggg06
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:ROBggg06
Alternative URL:http://dx.doi.org/10.1029/2005GC001138
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3959
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:20 Jul 2006
Last Modified:26 Dec 2012 08:57

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