In pedogenesis, translocations refer to the movement of materials within the soil profile. Which horizon is typically formed by clay illuviation due to translocations?

• A. A horizon
• B. Bt horizon
• C. C horizon
• D. O horizon

Answer: (B)

Clay illuviation occurs when fine clay particles move downward with percolating water and accumulate in a lower mineral layer. When this downward movement concentrates clay in a horizon, that layer becomes enriched in clay and often shows argillan coatings and a distinct boundary with the horizon above. This well-known subsoil layer is the Bt horizon, also called an argillic horizon, signaling clay illuviation. The O horizon is organic material on the surface, the C horizon is largely unweathered parent material, and the A horizon is the upper mineral soil where clay is typically not accumulating but may be lost through eluviation. So the horizon formed by clay illuviation is the Bt horizon.