Chronology of Soils

A timetable for an evolving soil on a geologic time scale, apart from recent anthropic (man‐made) modification, depends on:

• a. Parent material (which may be the geological bed‐rock, or wind‐blown cover such as loess or sand dunes, or littoral accumulations such as beachridges, or alluvial deposits associated with flood plains).

• b. Zonal climate (which may be roughly stated as “latitude”, but more precisely modified by oceanicity, or maritimicity, continentality, altitude and aspect, i.e., exposure to insolation, fetch, and prevailing wind).

• c. Geomorphic history (which generally spans the period of time since the latest ice ages, thus in North America and Europe since about 12 000 years ago, but in South America, South Africa, India and Australia, about 265 Myr. ago. Even more for North Africa and much of Arabia, where it is 445 Myr).

Study of these three variables is integral to what constitutes “Soil Stratigraphy”, a science that for understandable reasons found its birthplace in...