Extreme Acidic Environments Associated with Carbonate Mound Springs in the Great Artesian Basin, South Australia

A reduction in the piezometric surface of the western part of the Great Artesian Basin in Australia has led to reductions in flow from the iconic travertine mound springs. This has led to oxidation of sub-aqueous sulfidic soils in the discharge zone and in some cases extreme soil acidification (pH < 1). Net acidities are extremely high (>20,000 mol H+/tonne) and oxidation has induced intense weathering of the soils and adjacent carbonate mounds. Concomitant high evaporation rates have led to the development of thick layers of rare hydroxysulfate efflorescent minerals, which are highly soluble stores of acidity and metals. Preliminary Fe isotope data show significant fractionation associated with the oxidation and transport of Fe in soil profiles.