Structural and Crystal-Chemical Features and Rb–Sr Age of Globular Glauconite in the Ust-Il’ya Formation (Lower Riphean, Anabar Uplift)

• Published in: Lithology and Mineral Resources Vol. 55; no. 6; pp. 468 - 485
• Main Authors: Zaitseva, T. S., Ivanovskaya, T. A., Sakharov, B. A., Zviagina, B. B., Dorzhieva, O. V.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.11.2020; Springer Nature B.V
• Subjects: Analytical methods; Cations; Chemical analysis; Crystal structure; Crystals; Data; Dating; Diagenesis; Distribution; Earth and Environmental Science; Earth Sciences; Friability; Geochronology; Glauconite; Globules; Heterogeneity; Infrared spectroscopy; Isotopes; Lithology; Massifs; Mineral Resources; Mineralogy; Parameter identification; River mouth; River mouths; Rivers; Sedimentology; Sediments; Short range order; Smectites; Stratigraphy; Unit cell; Uplift; Vermiculite; Vermiculites; mineralogy; Anabar; crystal chemistry; glauconite; Rb‒Sr age; Lower Riphean
• ISSN: 0024-4902; 1608-3229; 1573-8892
• DOI: 10.1134/S0024490220060103

For the first time, mineralogical, structural, crystal-chemical and isotope-geochronological data were obtained for a glauconite sample from the Lower Riphean Ust-Il’ya Formation on the Magan River (western slope of the Anabar Massif, northern Siberia). It has been established that glauconite from the lenticular layer of friable glauconitite (glauconite grains ≥80%) contains two populations of mixed-layer crystals, in which mica layers (93%) alternate with either smectite-type (7%) or vermiculite-type layers (7%) with the short-range order factor R = 3. The ratio K Al = ( VI Al / ( VI Fe 3+ + VI Al) equal to 0.45 allows identifying the micaceous mineral as glauconite with the unit-cell parameter b = 9.065 Å and K 2 O content of 8.29%. Comparison of new data with the previously obtained mineralogical and crystal-chemical characteristics of Ust-Il’ya glauconites from the Kotuikan River section (2.5 km above the Il’ya River mouth), located 65 km south of the Magan River section, showed both similarities and differences. Analysis of the crystal-chemical heterogeneity of Kotuikan glauconite samples from rocks of different lithological types revealed peculiarities in the distribution of individual mica varieties composing the glauconite globules. Isotopic dating of glauconite from the Magan River section was performed in combination with simulation of the distribution of octahedral cations and comparison of the results obtained with Mössbauer and infrared (IR) spectroscopy data. Such an approach combined with the mineralogical and crystal-chemical analyses contributes to correct interpretation of the stratigraphic significance of isotope data. The results obtained provide grounds for the conclusion that isotopic dates of glauconite from the Magan section (1474 ± 21 Ma) coincides within the error limit with the earlier Rb–Sr and K–Ar dating of the Ust-Il’ya Formation (1485 ± 13 and 1459 ± 20 Ma, respectively) based on the glauconite in the Kotuikan section (Zaitseva et al., 2016). The former value marks the stage of early diagenesis of sediments and is suitable for estimating the age of this formation.