Partial Dissolution of Glauconitic Samples: Implications for the Methodology of K-Ar and Rb-Sr Dating

Abstract

The K-Ar dating of glauconite has been used as an important stratigraphic tool for many decades. The application of this technique is limited to pure glauconites, free of detrital contamination by K-bearing phases, often not easy to detect. This study extends the application of isotope dating to the contaminated glauconites and offers a precise technique for detecting the detrital contamination of glauconites.The most common K-bearing detrital contaminants have smaller (K-feldspars, Al-rich dioctahedral micas) or greater (trioctahedral micas) dissolution rates than glauconite in extremely low pH solutions. The differences in the dissolution rates can be applied to evaluate the purity of the glauconite and its crystallization age.The interlaboratory GLO glauconite standard and grain-size fractions separated from glauconitic sandstones of the Paleogene (sample GL) and Jurassic (sample GW8) ages were treated with acid (3M HCl, at 99±2°C) for different reaction times (0.5–7 h) and measured for their apparent isotopic ages.Microporous amorphous silica with large specific surface area is the solid product of the reaction and its content increases with reaction time. The K-Ar dates (apparent ages) of the solid residues increase significantly with reaction time: from 44.6 to 107 Ma for the GL sample and from 125.7 to 394.7 Ma for GW8. The increase is negligible in the case of the GLO standard. The Rb-Sr data of the GL sample were modeled using initial 87Sr/Sr ratios of 0.707–0.709, which resulted in a 29.9–35.8 Ma date for the untreated portions of GL, and ∼42.6 Ma after 7 h of treatment.The increase of isotopic K-Ar date with increasing time of dissolution is interpreted to be a result of increasing concentration of detrital, acid-resistant, K-bearing minerals, observed also with the electron microscope and X-ray diffraction. Probabilistic modeling based on single (K-Ar) or double (K-Ar and Rb-Sr) isotopic systems evaluated the isotopic ages of the detrital and authigenic minerals, and their K2O and Rb concentrations. The crystallization ages computed using these two methods are: 24.0, 26.5, and 32.3 Ma for the GL material, and 117.3–121.8 Ma for the GW8 series.The proposed method based on partial dissolution is a potential tool for evaluating the reliability of glauconite dating.

Mono and Poly-Cationic Adsorption of Heavy Metals Using Natural Glauconite

“…The total mass loss reached 9.5%. Two last, weak, and blurred thermal effects might be attributed to the young geological age (tertiary period) and ordered crystallographic structure of the glauconite, which has been confirmed by radiometric studies [26].…”

“…The total mass loss reached 9.5%. Two last, weak, and blurred thermal effects might be attributed to the young geological age (tertiary period) and ordered crystallographic structure of the glauconite, which has been confirmed by radiometric studies [26]. The DTA/TG thermal analysis revealed a clear endothermic effect associated with the presence of molecular water at a temperature range of 100 to 200 °C, with a maximum temperature at 145 °C ( Figure 3).…”

K-Ar Age Constraints on the Origin Of Micaceous Minerals in Savannah River Site Soils, South Carolina, USA

“…Thompson and Hower (1973) and Aronson and Douthitt (1986) found that extraction with dilute acid at 80ºC removes strongly bound K from micaceous interlayers of glauconite and illite only very slowly. Derkowski et al (2009) showed that authigenic Fe clays (glauconitic) are removed by stronger acid treatments (3 mol dm À3 HCl at~100ºC), which causes the age values of the residues to be greater than the glauconite age values when acid-resistant, older Al-rich detrital material is present. That is consistent with the effect of Vol.…”

Sorption of Heavy Metal Ions of Chromium, Manganese, Selenium, Nickel, Cobalt, Iron from Aqueous Acidic Solutions in Batch and Dynamic Conditions on Natural and Synthetic Aluminosilicate Sorbents

“…Then they were expanded and three fractions were chosen for the research—super fine (SF—to 1mm), fine (F—1–2 mm) and medium (M—2–4 mm). Glauconite was magnetically separated from tertiary sandy sediments of the Lublin Upland (Poland)—Nowodwór Mine (63–125 µm) [ 42 ]. Bentonite was a commercial product purchased form Sigma-Aldrich (St. Louis, MO, USA) and had particles diameter <0.2 mm.…”