[1] Gleysols occur within a wide range of unconsolidated materials, mainly fluvial, marine and lacustrine sediments of Pleistocene or Holocene age, having basic to acidic mineralogy.
Wetness is the main limitation on agriculture of virgin gleysols;[citation needed] these are covered with natural swamp vegetation and lie idle or are used for extensive grazing.
An estimated 200 million hectares of gleysols are found in the tropics, mainly in the Amazon region, equatorial Africa, and the coastal swamps of Southeast Asia.
On exposure, as the iron in the soil oxidizes colors are transformed to a mottled pattern of reddish, yellow or orange patches.
A reducing environment exists in the saturated layers, which become mottled greyish-blue or greyish-brown due to its ferrous iron and organic matter content.