Exceptional halite speleothem variety in a limestone environment: Goat Cave, Nullarbor (Western Australia)

Major discoveries in Goat Cave (6N-745, Hampton Tableland, Nullarbor, Western Australia) between 2022 and 2025 have brought this limestone cave, originally a doline with underlying large entrance chamber and passages totalling 300 m long and 40 m deep, to reach a development of 9.7 km and depth of 94 m. It is a complex carbonate cave system with a lateral extent of about 1800 m from WSW to ESE and several close-to-horizontal levels. Despite being a cave carved in fossiliferous Tertiary limestones with some calcite speleothems, it hosts a large variety of halite speleothems, along with minor gypsum and calcite speleothems. The halite and gypsum salts derive from meteoric waters brought inland by rainfall enriched in Na+ , Cl− , and SO4 2− , and other ions, as shown by historic rainfall analyses and as indicated by sulphur isotope analyses. The uplift of seawater-derived (sea salt) aerosols high into the troposphere increases the concentration of ions in rainwater, and brings these dissolved salts into the continent, with generally decreasing amounts at increasing distance from the coastline. The salt and sulphate ions resulting from rainfall since the Nullarbor limestones emerged from the ocean ~14 Ma were gradually brought deeper into the limestone during infiltration events. These salts re-appear as halite and gypsum speleothems in the currently dry caves of the Nullarbor. Goat Cave arguably hosts the most abundant and diverse display of halite speleothems in the Nullarbor. Despite being in a limestone cave, the speleothems of Goat Cave rival the secondary salt deposits of the famous halite caves of Iran, Israel and Atacama in Chile. Moreover, the dry and salty deep subterranean environment has allowed the preservation of a stunning abundance and variety of mummified invertebrates and mammals.