Articles | Volume 14, issue 6
Biogeosciences, 14, 1721–1737, 2017
Biogeosciences, 14, 1721–1737, 2017

Research article 31 Mar 2017

Research article | 31 Mar 2017

Geochemical and microstructural characterisation of two species of cool-water bivalves (Fulvia tenuicostata and Soletellina biradiata) from Western Australia

Liza M. Roger1,2, Annette D. George1, Jeremy Shaw2, Robert D. Hart2, Malcolm Roberts2, Thomas Becker2,3, Bradley J. McDonald4, and Noreen J. Evans4 Liza M. Roger et al.
  • 1School of Earth Sciences, the University of Western Australia, Crawley 6009, Australia
  • 2Centre for Microscopy, Characterisation and Analysis, the University of Western Australia, Crawley 6009, Australia
  • 3Department of Chemistry, Nanochemistry Research Institute, Curtin University, GPO Box U1987, Perth 6845, Australia
  • 4Department of Applied Geology, John de Laeter Centre, TIGeR, Curtin University, Bentley 6102, Australia

Abstract. The shells of two marine bivalve species (Fulvia tenuicostata and Soletellina biradiata) endemic to south Western Australia have been characterised using a combined crystallographic, spectroscopic and geochemical approach. Both species have been described previously as purely aragonitic; however, this study identified the presence of three phases, namely aragonite, calcite and Mg-calcite, using XRD analysis. Data obtained via confocal Raman spectroscopy, electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) show correlations between Mg ∕ S and Mg ∕ P in F. tenuicostata and between Sr ∕ S and S ∕ Ba in S. biradiata. The composition of the organic macromolecules that constitute the shell organic matrix (i.e. the soluble phosphorus-dominated and/or insoluble sulfur-dominated fraction) influences the incorporation of Mg, Sr and Ba into the crystal lattice. Ionic substitution, particularly Ca2+ by Mg2+ in calcite in F. tenuicostata, appears to have been promoted by the combination of both S- and P-dominated organic macromolecules. The elemental composition of these two marine bivalve shells is species specific and influenced by many factors, such as crystallographic structure, organic macromolecule composition and environmental setting. In order to reliably use bivalve shells as proxies for paleoenvironmental reconstructions, both the organic and inorganic crystalline material need to be characterised to account for all influencing factors and accurately describe the vital effect.

Short summary
The shell compositions of bivalve species from south Western Australia are described here to better understand the factors involved in their formation. The shell composition can be used to reconstruct past environmental conditions, but certain species manifest an offset compared to the environmental parameters measured. As shown here, shells that experience the same conditions can present different compositions in relation to structure, organic composition and environmental conditions.
Final-revised paper