Testing the applicability of vacuum-encapsulated 40Ar/39Ar geochronology to pedogenic palygorskite and sepiolite |
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| Institution: | 1. W.M. Keck Science Department, Claremont McKenna, Pitzer, and Scripps Colleges, 925 N. Mills Ave, Claremont, CA 91711, USA;2. UNLV Department of Geoscience, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010, USA;3. UNLV Department of Chemistry, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010, USA;1. Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China;2. Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA;3. China Conservation & Research Centre for the Giant Panda, Wolong 623003, China;1. Department of Bioengineering, University of California, Riverside, CA 92521, USA;2. Materials Science & Engineering Program, University of California, Riverside, CA 92521, USA;3. School of Materials and Metallurgy, Northeastern University, Shenyang 110004, People’s Republic of China;4. Department of Chemical Engineering, University of California, Riverside, CA 92521, USA;5. Stem Cell Center, University of California, Riverside, CA 92521, USA;1. Department of Bioengineering, University of California, Riverside, CA 92521, USA;2. Department of Microbiology, University of California, Riverside, CA 92521, USA;3. Materials Science and Engineering Program, University of California, Riverside, CA 92521, USA;4. Stem Cell Center, University of California, Riverside, CA 92521, USA;1. Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John''s, NL, A1B 3X7, Canada;2. Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA, USA;1. ZMT – Leibniz Center for Tropical Marine Ecology, Bremen, Germany;2. MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany;3. BGR – Federal Institute for Geosciences and Natural Resources, Hannover, Germany;4. AWI – Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany |
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| Abstract: | The difficulty of isolating intact, mineralogically pure pedogenic crystals from cemented soil is one of the most significant obstacles to quantifying rates of soil formation, geomorphic processes, and climate change in arid regions. We evaluate the applicability of vacuum encapsulated 40Ar/39Ar geochronology to pedogenic palygorskite and sepiolite extracted from the 4 to 5 Ma, extant Mormon Mesa petrocalcic soil-geomorphic surface of southern Nevada, and from the 780 ka to 2 Ma Jornada Experimental Range La Mesa soil-geomorphic surface near Las Cruces, New Mexico. Selective dissolution of cements using NaOAc and Tiron, accompanied by particle size fractionation, was used to isolate the pedogenic Mg-phyllosilicates. Scanning electron microscopy, inductively-coupled plasma spectrometry, X-ray diffraction, gas chromatograph mass spectrometry, and Ar isotope analysis were used to determine whether extraction impacted palygorskite/sepiolite suitability for 40Ar/39Ar geochronology. We found no adverse morphological or mineralogical effects, but meaningful ages could not be obtained due to small amounts of old, detrital phyllosilicates in the samples. While the potential of pedogenic palygorskite and/or sepiolite for geochronology now seems limited, results from this study may prove relevant for samples from other, non-pedogenic surface environments. It is hoped that this work will encourage further research towards successful 40Ar/39Ar geochronology of pedogenic phyllosilicates, as well as inform future geochemical or isotopic studies of individual pedogenic mineral species. |
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