palaeosols

Palaeosols are ancient soils preserved within the geological record. They form when a surface capable of soil formation is buried by subsequent sedimentation, volcanism, or evaporites, so that pedogenic features are preserved rather than erased by erosion. Paleosols can be found in sandstone, mudstone, coal beds, volcanic ash layers, and other sedimentary rocks. Burial and low disturbance are required to maintain horizon integrity over time.

Diagnostic features include preserved soil horizons (often an A or E-like surface overlain by a Bt-like horizon with clay illuviation, or caliche and other cemented horizons), root traces, burrows, and soil aggregates typical of pedogenesis. Paleosols may also show geochemical and mineralogical changes such as iron oxide coatings, clay mineral transformations, and pedogenic carbonates. Not all features survive in every case, and many paleosols are partially recrystallized or deformed by subsequent burial.

Paleosols provide records of past environments and climates because pedogenic processes respond to moisture, temperature, and vegetation. Well-developed horizons and caliche nodules can indicate particular climatic conditions, while carbonate nodules or strong illuviation relate to hydrological regimes. Isotopic and mineralogical analyses of paleosols can yield quantitative constraints on past temperatures and precipitation.

Paleosols occur worldwide in the sedimentary record, from ancient shield regions to basins, across a broad temporal range from the Paleozoic to the Cenozoic. They are studied in paleopedology and sedimentology and have applications in reconstructing past environments as well as in petroleum geology and groundwater history.