Field and mineralogical investigations of ferricretes, silcretes and red-brown hardpans across a wide range of arid and semiarid landscapes in Australia reveal a variety of ferruginous and siliceous horizons and crusts, referred to herein as “Fe-Si-duricrusts. Their geomorphic and stratigraphic relationships with bedrock, sediments and soils indicate formation throughout long intervals of geological time in landscapes, which are also characterised by various zones of bleached and iron-mottled materials.  

Ferricretes have traditionally been interpreted as evidence of former tropical climates under so-called humid tropical climates.  Silica is generally leached from profiles while iron and aluminium is retained and concentrated. In recent years this interpretation has been challenged based on current studies involving the contemporary geochemistry and mineralogy of Acid Sulfate Soils and acid groundwaters, which are important for understanding: (i) accelerated weathering and (ii) precipitation of cementing minerals that form Fe-Si-duricrusts in Australian arid and semiarid landscapes.  It may be that Fe-Si-duricrusts can form as the result of weathering processes in Acid Sulfate Soils under temperate climates like those of the very present day.

The characteristics of Acid Sulfate Soils, which are common in the contemporary landscapes, provide the framework for models involving likely multiple stages in the development of these Fe-Si-duricrusts.