The Gray Luvisol in this image has a sharp contact between the overlying leaf litter horizon (LFH) and the bleached grayish Ae horizon due to the absence of organisms to mix the organic and mineral layers together. The bleached Ae is underlain by the Bt, which has a higher percentage of clay than the Ae. Because of the higher clay content the Bt often has more strongly developed soil structure (larger and firmer peds) as well . The transitional BC horizon is underlain by a Cca horizon where the calcium carbonate lost from the Ae and Bt has re-precipitated.
Contributor: Darwin Anderson
In the Gray Brown Luvisols the overlying leaf litter (LFH) has been mixed into the uppermost mineral layer by earthworms and other soil-dwelling organisms, creating an Ah horizon. This horizon is underlain by the Ae/Bt sequence diagnostic of the Luvisols. The Ae has lower clay content than the Bt, creating the texture contrast horizon. The thick Bt is underlain by a Ck horizon, which has calcium carbonate levels inherited from the parent material.
Contributor: Soils of Canada slide set