calcareous adj : composed of or containing or resembling calcium carbonate or calcite or chalk [syn: chalky]
Calcareous refers to a sediment, sedimentary rock, or soil type which is formed from or contains a high proportion of calcium carbonate in the form of calcite or aragonite.
Calcareous rock also refers to sediments derived near land. The carbon content is high due to life-derived sediments. The farther from land sediments fall, the less calcareous they are, usually. There are of course exceptions. Some areas can have inter bedded calcareous sediments due to storms or changes in ocean currents.
It is also used to refer to relatively alkaline soil. Frequently this is indeed due to a high calcareous content but there are other causes for a high soil pH.