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USGS · 70038294

Extension of 239+240 Pu sediment geochronology to coarse-grained marine sediments

Steven A. Kuehl·Michael E. Ketterer·Jennifer L. Miselis
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Abstract

Sediment geochronology of coastal sedimentary environments dominated by sand has been extremely limited because concentrations of natural and bomb-fallout radionuclides are often below the limit of measurement using standard techniques. ICP-MS analyses of 239+240 Pu from two sites representative of traditionally challenging (i.e., low concentration) environments provide a "proof of concept" and demonstrate a new application for bomb-fallout radiotracers in the study of sandy shelf-seabed dynamics. A kasten core from the New Zealand shelf in the Southern Hemisphere (low fallout), and a vibracore from the sandy nearshore of North Carolina (low particle surface area) both reveal measurable 239+240 Pu activities at depth. In the case of the New Zealand site, independently verified steady-state sedimentation results in a 239+240 Pu profile that mimics the expected atmospheric fallout. The depth profile of 239+240 Pu in the North Carolina core is more uniform, indicating significant sediment resuspension, which would be expected in this energetic nearshore environment. This study, for the first time, demonstrates the utility of 239+240 Pu in the study of sandy environments, significantly extending the application of bomb-fallout isotopes to coarse-grained sediments, which compose the majority of nearshore regions.

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Steven A. Kuehl, Michael E. Ketterer, Jennifer L. Miselis. 2012. Extension of 239+240 Pu sediment geochronology to coarse-grained marine sediments. https://doi.org/10.1016/j.csr.2012.01.016

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