Geochemical and C, O, Sr, and U-series isotopic evidence for the meteoric origin of calcrete at Solitario Wash, Crater Flat, Nevada, USA |
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Authors: | L A Neymark J B Paces B D Marshall Z E Peterman J F Whelan |
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Institution: | (1) US Geological Survey, Denver Federal Center, Box 25046, M.S. 963 Denver, CO 80227, USA |
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Abstract: | Calcite-rich soils (calcrete) in alluvium and colluvium at Solitario Wash, Crater Flat, Nevada, USA, contain pedogenic calcite
and opaline silica similar to soils present elsewhere in the semi-arid southwestern United States. Nevertheless, a ground-water
discharge origin for the Solitario Wash soil deposits was proposed in a series of publications proposing elevation-dependent
variations of carbon and oxygen isotopes in calcrete samples. Discharge of ground water in the past would raise the possibility
of future flooding in the unsaturated zone at Yucca Mountain, Nevada, site of a proposed high-level nuclear waste repository.
New geochemical and carbon, oxygen, strontium, and uranium-series isotopic data disprove the presence of systematic elevation-isotopic
composition relations, which are the main justification given for a proposed ground-water discharge origin of the calcrete
deposits at Solitario Wash. Values of δ13C (−4.1 to −7.8 per mil ‰]), δ18O (23.8–17.2‰), 87Sr/86Sr (0.71270–0.71146), and initial 234U/238U activity ratios of about 1.6 in the new calcrete samples are within ranges previously observed in pedogenic carbonate deposits
at Yucca Mountain and are incompatible with a ground-water origin for the calcrete. Variations in carbon and oxygen isotopes
in Solitario Wash calcrete likely are caused by pedogenic deposition from meteoric water under varying Quaternary climatic
conditions over hundreds of thousands of years. |
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Keywords: | Calcrete C O Sr and U-series isotopes Nuclear waste repository Crater Flat Yucca Mountain Nevada |
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