Local structure of Zn in Cretaceous-Tertiary boundary clay from Stevns Klint

Abstract

The local structure around zinc atoms in Cretaceous-Tertiary (K-T) boundary clay from Stevns Klint, Denmark, was studied by Zn Kedge XAFS spectroscopy. XAFS measurements were performed at the BL-12C and BL-9C beamlines at the Photon Factory in the High Energy Accelerator Research Organization (KEK), Japan. The local structure around Zn in the K-T clay resembles the framework structure of the tetrahedral ZnO 4 site in the zinc silicate willemite, judging from first shell Zn-O and second shell Zncation distances [1.953(3) and 3.51(2) Å, respectively], Xray absorption near edge structure (XANES) spectra, and radial structure function. The Debye-Waller factor σ 2 of the K-T clay sample is similar to those for the tetrahedral sites in crystalline phases, where Zn occupies mainly tetrahedral sites. The local structure of Zn in the K-T clay is peculiar and differs from that found in many clay minerals.

XAFS study of Zr in Cretaceous–Tertiary boundary clays from Stevns Klint

“…It should be suggested that local structures of Zr in K-T clays maintain the glass structure (not crystalline because of high forming temperature for many Zr minerals) and remain the thermal quenching records at meteorite impact of K-T boundary age. Since local structure of Zr in K-T clays kept glass structure, the recrystallization by the weathering, precipitation and diagenesis are not observed on the local structure around Zr ions, which different from previous researches on the local structure around As and Zn (Sakai et al, 2007;Okube et al, 2012). This may relate to existence of stable hydrate phase for Zr.…”

“…Glass structure is affected by pressure and temperature condition existing during the glass formation process (Stebbins and McMillan, 1989;Paris et al, 1994;Mysen and Neuville, 1995;Yarger et al, 1995). Sakai et al (2007) and Okube et al (2012) presented interesting results on the local structure around As and Zn in K-T clays by XAFS experiments, respectively. XANES and EXAFS studies of the local structure around Zr in K-T boundary clays will be expecting to provide more comprehensive data such as forming temperature, pressure and quenching history on the impact and extinction event.…”

“…Analytical point was the same layer as that studied by Okube et al (2012). In order to study the local structure around Zr atoms in K-T boundary clays, we prepared several reference natural zirconium minerals and glasses such as, zircon (ZrSiO 4 ), PbZrO 3 , SrZrO 3 , volcanic glasses (obsidian and pitch stone), tektite (indochinite) and impact-related glasses [suevite and libyan desert glass (LDG)].…”

XAFS study of Sb and As in Cretaceous–Tertiary boundary sediments: an index of soiling of the global environment with dust and ashes from impact ejecta falls

“…However, the origins, concentration processes, and the geochemical and environmental behaviors of Sb are not well known. Sakai et al (2007) and Okube et al (2012) clarified the local structures around As and Zn atoms in K-T boundary sediments from Stevns Klint using XAFS analyses. They proposed that As occupies the tetrahedral AsO 4 site in ferrihydrite and Zn occupies the tetrahedral ZnO 4 site in a willemite-like framework structure.…”

“…They proposed that As occupies the tetrahedral AsO 4 site in ferrihydrite and Zn occupies the tetrahedral ZnO 4 site in a willemite-like framework structure. Okube et al (2012) also proposed that precipitation of Zn took place under high pH conditions, such as in seawater. Furthermore, Miyano et al (2016) determined the local structures of Ca, Cr, Mn, Fe, and Ni atoms in K-T boundary sediments and clarified the effects of weathering, diagenesis, and life activity under the sedimentation.…”