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 K-edge 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 ZnO₄ site in the zinc silicate willemite, judging from first shell Zn-O and second shell Zn-cation distances [1.953(3) and 3.51(2) Å, respectively], X-ray absorption near edge structure (XANES) spectra, and radial structure function. The Debye-Waller factor σ² 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.