caliche

Caliche is a hardened layer within soil or regolith that is largely composed of calcium carbonate (CaCO3). It forms when calcium-rich waters move through the profile and precipitate carbonate minerals near or at the surface, creating nodules, crusts, or a continuous hard horizon. In many regions it is referred to as calcrete (especially in Australia) or as a duricrust when it becomes cemented and durable. Caliche horizons are commonly called Bk or Bt horizons in soil profiles and can significantly alter soil properties.

Formation occurs through pedogenic processes driven by aridity. Evaporation concentrates dissolved calcium and carbonate, promoting precipitation. Repeated cycles of dissolution, transport, and precipitation can produce various textures, from nodular aggregates to thick, cemented layers that may cement sand grains and reduce porosity. Caliche can range from shallow to several meters deep and often impedes root growth, water movement, and tillage.

Global distribution is wide in arid and semi-arid regions, including parts of the southwestern United States, northern Mexico, the Andes and other parts of South America, Africa, the Middle East, Central Asia, and Australia. Its presence influences soil management and hydrology by restricting deep rooting and altering permeability. Caliche can also act as a groundwater confining layer in some settings.

Human use and significance vary by region. Caliche deposits have historically provided lime for agricultural or construction purposes in some areas. In geology and soil science, caliche serves as a record of past climatic conditions and soil-forming processes. It is distinct from silica-cemented duripans and other non-carbonate duricrusts.