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

A combined ultrasonic treatment, with de-ionized H2O, dilute HAc or HCl, of three Mid-Miocene glauconite samples was applied to K–Ar date the different separates in order compare results those obtained by Rb–Sr method using same and that were analyzed strictly way. Two aliquots yield opposite elemental trends, which suggests initial mineral compositions for various pellets. The data two untreated leached L7 L8 are almost within analytical uncertainty from 17.3 ± 0.6 Ma 19.6 0.7 (2σ), while third L10 sample slightly higher at 22.1 1.2 (2σ). Comparatively, earlier published ages gave similar an isochron 18.1 3.1 (2σ) age 1.8 Ma, aliquot yields a very high 42.1 1.6 Ma. This fraction contains blödite, Sr-rich carbonate impacted isotopic systems differently. Generally, HCl acids dissolve carbonates, sulfates, sulfites oxides, they do not affect clay-type crystals such as glauconites. These soluble minerals can be identified indirectly, here, X-ray diffraction amounts Na2O, CaO Fe2O3 contents. Together leaching some metallic trace elements, NaO confirm metals blödite both hosted occurrence this Sr-enriched explains differences non-treated systematic any separate before isotope determination and, possibly, comparison results. Ultrasonic shaking appears appropriate physical disaggregation contaminating grains may remain pellets, even after preliminary H2O wash, remove but H2O-insoluble silicates. study completed here complement previous highlights, again, importance preparation step studies glauconite-type extension, clay material, all occurring interfere final determinations therefore, differently assemblages. All equilibrium need removed analysis, including Sr alkali-enriched ones.