Which soil order exhibits minimal horizon development, mostly retaining the A horizon?

Entisols are characterized by minimal horizon development and often primarily display an A horizon. This soil order typically forms in environments where soil formation processes are limited, such as steep slopes, recent floodplains, or areas with unstable surfaces. Because of these conditions, Entisols do not develop deeper layers or significant vertical stratification, which is a defining feature of more mature soils.

In contrast, Inceptisols show some degree of horizon development and have a more established structure, indicating they have undergone more weathering and formation than Entisols. Gelisols are associated with permafrost and exhibit distinct horizons that reflect the cold climate conditions they form in. Histosols, primarily composed of organic material, have a saturated, thick O horizon rather than a well-defined A horizon. Hence, they represent a different type of soil development entirely, focused on organic material accumulation.

Overall, the primary distinguishing factor for Entisols is their tendency to maintain only the A horizon with little to no evidence of further horizon development.