The correct option is Illuviation.
Explanation
Soil formation (pedogenesis) involves the vertical movement of materials within the soil profile. This process, known as translocation, leads to the differentiation of soil horizons through the removal and accumulation of minerals and organic matter.
Detailed Analysis:
- Eluviation Eluviation (Incorrect): This refers to the removal or washing out of soil materials (such as clay, humus, or iron oxides) from the upper layers of the soil to the lower layers. It typically occurs in the upper horizons (often labeled the E horizon).
- Illuviation Illuviation (Correct): This is the process of deposition or accumulation of soil materials in the lower layers of the soil profile. Materials leached from the upper horizons (via eluviation) are deposited here, typically forming the B horizon (subsoil).
- Carbonation Carbonation (Incorrect): This is a type of chemical weathering where carbon dioxide dissolves in water to form carbonic acid, which then reacts with carbonate minerals (like limestone). It is a weathering process, not a soil deposition process.
- Humification Humification (Incorrect): This is the process of decomposition of organic matter to form humus. It relates to the biological breakdown of plant and animal residues, not the vertical transport and deposition of mineral particles.
Key Takeaway:
Eluviation is the exit (loss) of material from a soil layer, while Illuviation is the accumulation (gain) of material in a lower layer. A helpful mnemonic is: Eluviation = Exit; Illuviation = In.