Furniture alterite zones — Métropole

Areas in which the presence (or absence) of movable altered geological formations has been identified or is assumed. In the broadest sense, altered formation is a geological formation “having undergone, because of the action of water, changes in its original chemical and mineralogical composition but also its physical properties (mechanical, electrical, elastic, hydrogeological)”. These alterations may be: — Subtractives (net exportation of material under the effect of leaching) resulting in lateral profiles and their bauxitic variant on silicated rocks; — Additives (net input of matter) resulting in precipitation forming silcrete-type crusts, calcretes... The area mapped here is limited to the “saprolite”, a generally clay-dominated movable horizon, constituting the upper part of a laterite profile developed on metamorphic, plutonic or volcanic rocks. We are therefore only interested in alteration in its subtractive form and in base context only within the meaning of the BDLISA repository, namely within the magmatic and metamorphic geological formations. (According to Sandre, dictionary of the hydrogeological reference SAQ V 2.2)