Origin

Carbonates are dominantly derived directly from the parent material and occasionally they are formed by weathering of minerals present in the parent material (in both cases they are said to be autochthonous). In other cases the carbonates originate from external sources, e.g. transported by wind or water (allochthonous).

Soil carbonates are subject to mobilization processes which leach them from the surface horizons. From a genetic point of view it is of great interest to distinguish a possible pedogenic origin (i.e. a vadose origin) of these accumulations from a geological provenance (i.e. freatic) of the carbonates of the parent material.

On a microscopic level some characteristic features may be reconized:

Very irregular distributions A very irregular distribution of soil carbonates is evident: some voids have a thick coatings, others a very thin or none at all. In the case of ground water deposits on the contrary the carbonate accumulations are much more uniform (all the voids bear similar coatings, very homogeneous inside a same pore).
Discontinous coatings The coatings of soil carbonates are sometimes interrupted, giving rise to discontinuous coatings.
Pendants Drying of the soil results in a larger retention of soil moisture below gravels, giving rise to the formation of pendants.
Bridged grains As a result of desiccation, soil solutions concentrate in the meniscs between grains, and carbonates precipitate, forming bridges.
Carbonates coating other pedofeatures In some cases the presence of carbonates covering other pedofeatures (e.g. clay coatings) is sufficient to prove their pedogenic origin.

Cappings Sometimes de pedology carbonates form a capping. The capping is a coating on the top of the grains or aggregates .

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