Which term describes Mollisols that are rich in organic matter?

Mollisols are a specific order of soil found primarily in grassland regions, characterized by a thick, dark surface horizon rich in organic matter, known as the mollic epipedon. The term "Mollic" specifically refers to this type of horizon. This horizon is typically more than 25 centimeters thick, dark in color (due to high organic content), and has a high base saturation, which contributes to the soil's fertility and ability to support plant growth.

In contrast, the other terms relate to different soil characteristics or horizons. "Udic" refers to a soil moisture regime that is relatively moist, "Argillic" refers to a horizon characterized by clay accumulation, and "Cambic" refers to a weakly developed horizon indicative of soil formation processes without significant clay accumulation or organic matter enrichment. Thus, "Mollic" is the appropriate term to describe those particular Mollisols that are rich in organic matter, reflecting the key characteristic that defines this soil order.