difference between A-horizon and B-horizon
Answers
Soil horizons form when a surface is stable and sedentary (i.e., not affected by active fluvial, pluvial, or aeolian processes).
The O horizon is the top layer and contains almost exclusively organic material.
The A horizon is directly beneath the O horizon and is usually what you'd call topsoil, being heavily enriched by decaying organic material but also depleted of other mineral deposits (such as calcium carbonate).
The E horizon is found between the A and B horizons only in well developed soils and has been depleted of mineral deposits but not enriched by organic material like the A horizon.
The B horizon is below the A (or sometimes E) horizon and is where all of the minerals accumulate. In particularly well-developed B horizons, you'll sometimes see a sub-horizon called a BK horizon, which is a well developed layer of calcium carbonate (especially in the southwest United States). This layer is often very hard and can be a hinderance to subsurface detection strategies like GPR.
The C horizon is simply the parent material that has not been affected by soil development.
The R horizon, as it's sometimes called, is the bedrock beneath any sediment present.