Which horizon is typically characterized by illuvial accumulation of materials like clay?

• A. B horizon is typically characterized by illuvial accumulation of materials like clay.
• B. A horizon is typically the top mineral horizon with humus.
• C. C horizon is partially weathered parent material.
• D. O horizon is the organic surface litter layer.

Answer: (A)

Materials moving down through the soil profile tend to collect in a deeper mineral layer, creating an illuvial horizon. This is the B horizon, where clay and other fine materials that were leached from above accumulate, giving it a denser texture and distinct color compared with the layers above. The A horizon is the top mineral layer rich in organic matter, the E horizon (if present) is an eluviation layer where materials are removed, the O horizon is the surface organic litter, and the C horizon is the partially weathered parent material. So the horizon typically showing illuvial accumulation of clay is the B horizon.