Uranium loss and aragonite–calcite age discordance in a calcitized aragonite stalagmite |
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| Institution: | 1. Department of Geoscience, Mailstop 4022, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154, USA;2. Centro de Geociencias, UNAM, Campus Juriquilla, Blvd. Juriquilla 3001, Juriquilla, Querétaro 76230, Mexico;3. Department of Earth and Planetary Science, University of New Mexico, 200 Yale Blvd. NE, Albuquerque, NM 87131, USA;1. Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland;2. Department of Earth Sciences, Durham University, Durham DH1 3LE, UK;3. Department of Earth Sciences, Cambridge University, Downing Street, Cambridge CB2 3EQ, UK;4. Institute of Environmental Physics, University of Heidelberg, Im Neuenheimer Feld 229, 69129 Heidelberg, Germany;5. Institute of Earth and Environmental Science, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany;6. Department of Physics, Laboratory of Ion Beam Physics, ETH Zurich, 8093 Zurich, Switzerland;7. Scottish Universities Environmental Research Centre (SUERC), East Kilbride, UK;8. Potsdam-Institute for Climate Impact Research,Transdisciplinary Concepts & Methods, Telegraphenberg A 31, 14473 Potsdam, Germany;9. Department of Physics,Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany;10. Dept. of Anthropology, University of New Mexico, Albuquerque, NM 87106, USA;11. Dept. of Anthropology, Institute for Energy and the Environment, The Pennsylvania State University, PA 16802, USA;12. Dept. of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA;1. School of Earth Sciences, University of Melbourne, Victoria, 3010, Australia;2. School of Land and Environment, University of Melbourne, Victoria, 3010, Australia;3. School of Physics, University of Melbourne, Victoria, 3010, Australia;1. Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing, 400715, China;2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an, 710075, China;3. Field Scientific Observation & Research Base of Karst Eco-environments at Nanchuan in Chongqing, Ministry of Land and Resources of China, Chongqing, 408435, China;4. Institute of Global Environmental Change, Xi''an Jiaotong University, Xi''an, 710049, China;5. Department of Earth Sciences, University of Minnesota, Minneapolis, MN, 55455, USA;6. Department of Geosciences, National Taiwan University, Taipei, 10617, Taiwan, ROC;7. Institut für Geologie, Universität Innsbruck, 6020 Innsbruck, Austria;1. Department of Earth Sciences, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455, USA;2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA;3. Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, USA;4. Department of Geosciences, University of Arizona, 1040 E. 4th St., Tucson, AZ 85721, USA;5. Department of Earth and Environmental Sciences, Boston College, 140 Commonwealth Ave., Chestnut Hill, MA 02467, USA;1. Institute for Geosciences, Johannes Gutenberg-University Mainz, J.-J.-Becher-Weg 21, 55128 Mainz, Germany;2. Biogeochemistry Department, Max Planck Institute for Chemistry, P. O. Box 3060, 55020 Mainz, Germany;3. MARUM – Center for Marine Environmental Sciences, University of Bremen, Leobener Str., 28359 Bremen, Germany;4. Geology and Geophysics Department, King Saud University, Riyadh, Saudi Arabia;1. Department of Earth Sciences, Durham University, DH1 3LE, United Kingdom;2. Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, United Kingdom;3. Laboratory for the Analysis of Radiocarbon with AMS (LARA), Department of Chemistry and Biochemistry, and Oeschger Centre for Climate Change Research, University of Bern, Freiestrasse 3, Bern, 3012, Switzerland;4. Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne, NE1 8ST, United Kingdom;5. School of Health & Life Sciences, Teesside University, Middlesbrough, TS1 3BX, United Kingdom;6. Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, United Kingdom;7. School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom;8. National Centre for Atmospheric Science and Department of Meteorology, University of Reading, RG6 6BB, United Kingdom;9. Durham Centre for Academic Development, Durham University, Durham, DH1 1TA, United Kingdom;10. Potsdam Institute for Climate Impact Research, Telegrafenberg, 14473, Potsdam, Germany;11. GFZ German Research Centre for Geosciences, Section ‘Climate Dynamics and Landscape Development’, Telegrafenberg, 14473, Potsdam, Germany |
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| Abstract: | We analyzed uranium-series concentrations and isotopic ratios in a mixed aragonite and calcite stalagmite from Juxtlahuaca Cave, from the Sierra Madre del Sur of Mexico. The U-series data for the aragonite layers return highly precise and stratigraphically correct ages over the past ca. 4300 years. In contrast, age determinations from calcite layers are too old by several hundred years relative to the precise aragonite ages, have analytical uncertainties an order of magnitude larger than aragonite ages, and yield ages that do not overlap the aragonite ages within analytical uncertainties. Based on geochemical and petrographic observations, we interpret the calcite layers to have formed from recrystallization of aragonite soon after primary aragonite deposition. Calcite occurs as discontinuous lenses on and off the growth axis, and laminae can be traced between aragonite and calcite layers, demonstrating that visible growth banding is not effaced in the recrystallization process. Paired aragonite-calcite U-series data from coeval stratigraphic layers demonstrate that uranium concentrations decrease by two orders of magnitude during calcitization, and result in decreased (234U/238U). Uranium loss during diagenesis mimics a need for an age correction using an initial 230Th/232Th ratio one to two orders of magnitude larger than the bulk Earth ratio of 4.4 ± 2.2 × 10−6. A need for apparent high initial 230Th/232Th ratios results from ingrowth of 230Th during 234U decay. |
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