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Article

Ultrasonic Shaking of Glauconite Pellets with Diverse Reagents for a Comparison of Their K–Ar with Already Published Rb–Sr Results

1
Institut des Sciences de la Terre et de l’Environnement, Université de Strasbourg (UdS/CNRS), 67084 Strasbourg, France
2
Department of Chemistry, Vrije Universiteit Brussel, BE-1050 Brussels, Belgium
3
Department of Geology, Faculty of Engineering, University of Istanbul-Cerrahpasa, Istanbul 34500, Turkey
*
Author to whom correspondence should be addressed.
Academic Editors: Suzanne Golding and Jesus Martinez-Frias
Geosciences 2021, 11(11), 439; https://doi.org/10.3390/geosciences11110439
Received: 28 August 2021 / Revised: 13 October 2021 / Accepted: 18 October 2021 / Published: 25 October 2021
(This article belongs to the Section Geochemistry)
A combined ultrasonic treatment, with de-ionized H2O, dilute HAc or dilute HCl, of three Mid-Miocene glauconite samples was applied to K–Ar date the different separates in order to compare the results with those obtained by the Rb–Sr method using the same three samples and that were analyzed strictly in the same way. Two aliquots yield opposite elemental and K–Ar trends, which suggests different initial mineral compositions for the various pellets. The K–Ar data of two untreated and leached L7 and L8 aliquots are almost within analytical uncertainty from 17.3 ± 0.6 Ma to 19.6 ± 0.7 Ma (2σ), while those of the third L10 sample are slightly higher at 22.1 ± 1.2 Ma (2σ). Comparatively, the earlier published Rb–Sr ages of the three untreated samples and of the leached aliquots gave similar data for the L7 aliquots by an isochron at 18.1 ± 3.1 (2σ) Ma and for the sample L8 by an isochron with an age of 19.6 ± 1.8 (2σ) Ma, while the untreated L10 aliquot yields a very high Rb–Sr date of 42.1 ± 1.6 (2σ) Ma. This untreated L10 glauconite fraction contains blödite, a Sr-rich carbonate that impacted the two isotopic systems differently. Generally, dilute HCl or HAc acids dissolve carbonates, sulfates, sulfites and oxides, while they do not affect the clay-type crystals such as glauconites. These soluble minerals can be identified indirectly, as here, by X-ray diffraction and the amounts of leached Na2O, CaO and Fe2O3 contents. Together with the leaching of some metallic trace elements, those of NaO confirm the leaching of metals and of blödite that are both hosted by the glauconite pellets. The occurrence of this Sr-enriched mineral explains the age differences of the non-treated aliquots and suggests a systematic leaching of any glauconite separate before isotope determination and, possibly, a comparison of the Rb–Sr and K–Ar results. Ultrasonic shaking appears appropriate for physical disaggregation of any contaminating grains that may remain hosted within the pellets, even after a preliminary H2O wash, which may dissolve and remove the soluble minerals but not the H2O-insoluble silicates. The K–Ar study completed here as a complement to a previous Rb–Sr study highlights, again, the importance of the preparation step in isotopic studies of glauconite-type and, by extension, of any clay material, as all occurring minerals can interfere in the final age determinations and, therefore, differently in the mineral assemblages. All those not in isotopic equilibrium need to be removed before analysis, including the soluble Sr or alkali-enriched ones. View Full-Text
Keywords: glauconite pellets; dilute acid leaching experiments; various ultrasonic treatments; various leaching reagents; major and trace chemical compositions; blödite; K–Ar ages; previously published Rb–Sr data glauconite pellets; dilute acid leaching experiments; various ultrasonic treatments; various leaching reagents; major and trace chemical compositions; blödite; K–Ar ages; previously published Rb–Sr data
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MDPI and ACS Style

Clauer, N.; Keppens, E.; Uysal, I.T.; Aubert, A. Ultrasonic Shaking of Glauconite Pellets with Diverse Reagents for a Comparison of Their K–Ar with Already Published Rb–Sr Results. Geosciences 2021, 11, 439. https://doi.org/10.3390/geosciences11110439

AMA Style

Clauer N, Keppens E, Uysal IT, Aubert A. Ultrasonic Shaking of Glauconite Pellets with Diverse Reagents for a Comparison of Their K–Ar with Already Published Rb–Sr Results. Geosciences. 2021; 11(11):439. https://doi.org/10.3390/geosciences11110439

Chicago/Turabian Style

Clauer, Norbert, Edward Keppens, I. T. Uysal, and Amélie Aubert. 2021. "Ultrasonic Shaking of Glauconite Pellets with Diverse Reagents for a Comparison of Their K–Ar with Already Published Rb–Sr Results" Geosciences 11, no. 11: 439. https://doi.org/10.3390/geosciences11110439

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