A characterisation of the coastal tufa deposits of south-west Western Australia

Located in the south-west coastal zone of Western Australia are numerous tufa deposits, which are registered as Threatened Ecological Communities (TEC). The tufas occur in near-shore shallow bedrock settings and are associated with local groundwater discharge. Depositional facies, mineralogy, elemental chemistry and water quality were investigated for five key deposits. Two conceptual environmental models are identified. The first, the cascade to barrage pool model is associated with coastal waterfall zones, the second, a perched spring-line and barrage pool model is located predominantly in the supratidal zone. Tufa morphology, texture, mineral composition and elemental chemistry vary within and between sites. Both phytoclast and lithoclast (allochthonous), and phytoherm forms of tufa are identified depending on location within the facies. Calcite, and to a lesser extent, aragonite and Mg-calcite dominate tufa mineralogy, with diagenetic modifications apparent. Tufa water chemistry is generally Na-Cl-HCO3 dominated; however, Na-Cl concentrations increase at sites situated within the supratidal zone. Currently the most likely potential threat posed to these deposits is increasing nutrient levels in spring waters from agricultural land use within the catchments. This could in the future impact on tufa development.