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Geochronology Advances in geochronological science
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Preprints
https://doi.org/10.5194/gchron-2020-20
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gchron-2020-20
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  03 Jul 2020

03 Jul 2020

Review status
A revised version of this preprint is currently under review for the journal GChron.

A Sample Characterization Toolkit for Carbonate U-Pb Geochronology

E. Troy Rasbury1, Theodore M. Present2, Paul Northrup1, Ryan V. Tappero3, Antonio Lanzirotti4, Jennifer M. Cole5, Kathleen Wooton1, and Kevin Hatton1 E. Troy Rasbury et al.
  • 1Department of Geosciences, FIRST, Stony Brook University, 100 Nichols Rd, Stony Brook, NY 11794, USA
  • 2Division of Geological and Planetary Sciences, California Institute of Technology, 307 North Mudd Laboratory, Pasadena, CA 91125, USA
  • 3NSLS-II, Brookhaven National Laboratory, Upton NY 11973, USA
  • 4Center for Advanced Radiation Sources, Randall, Chicago, IL 60637
  • 5Department of Science, West Los Angeles College, Culver City, CA 90230, USA

Abstract. Laser ablation U-Pb analyses of carbonate (LAcarb) samples has greatly expanded the potential for U-Pb dating to a variety of carbonate producing settings. Carbonates that were previously considered impossible to date using isotope dilution methods may preserve domains that are favorably interrogated when using spatially resolved laser ablation geochronology techniques. Work is ongoing to identify reference materials and to consider best practices for LAcarb. In this study we apply standard and emerging characterization toolsets on three natural samples with the dual goal of enhancing the study of carbonates and in establishing a new set of precisely characterized natural standards for LAcarb studies. We start with the existing carbonate reference material WC-1 from the Permian Reef Complex of Texas, building on the published description to offer a deeper look at U and fluids. We consider a tufa sample from the Miocene Barstow Formation of the Mojave Block, California, as a possible secondary calcite reference material due to its well-behaved U/Pb systematics. There are currently no natural dolomite standards. We present an unusual dolomite sample with very well-behaved U-Pb systematics from the Miocene of the Turkana Basin of Kenya as a possible dolomite reference material for LAcarb dating. In addition to using XRF mapping and spectroscopy to better understand U in these natural samples, we have analyzed multiple aliquots of each of them for 87Sr/86Sr. The Sr isotope compositions are reasonably homogeneous in all three samples, so that these could be used as Sr isotope standards as well. This combination could streamline split stream analyses of 87Sr/86Sr and U/Pb geochronology.

E. Troy Rasbury et al.

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E. Troy Rasbury et al.

E. Troy Rasbury et al.

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Latest update: 19 Oct 2020
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Short summary
We characterize three natural carbonate samples with elevated uranium/lead (U/Pb) ratios to demonstrate techniques for characterizing carbonates for U/Pb dating. With the rapidly accelerating application of laser ablation analyses, there is a great need for well-characterized standards. The three samples we describe have good potential as standards. In addition to U/Pb data, we present strontium (Sr) isotope analyses to demonstrate that these could be dual standards for U/Pb and Sr isotopes.
We characterize three natural carbonate samples with elevated uranium/lead (U/Pb) ratios to...
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