532
Climatic Geomorphology
Many bauxites can be considered as derived from leaching of old laterites. Tardy and
Roquin (1992) indicated that some aluminic laterites present two layers with gibbsite
enrichment: one near the saprolite profile base, almost in contact with the parent rock, and
the other at the profile top, near the soil surface.
Bauxitization increases with fluvial incision. It has also been observed that bauxites
show a better development along fault lines, which facilitate leaching processes. In many
cases the bauxite outcropping on an escarpment laterally wedges towards the lateritic
mass. This indicates that the bauxite does not form a continuous layer and is genetically
related to the escarpment evolution (McFarlane, 1983).
About 10% of the bauxites belong to the karstic type (Ollier and Pain, 1996). In these
cases the bauxite fills fissures, depressions, and cavities of the karstified carbonate rock.
Initially bauxites were thought to constitute insoluble residues from the dissolution of
calcareous massifs. It is difficult, however, to explain the source of important aluminium
quantities. Following Bardossy (1981), karstic depressions produced by differential
dissolution receive aluminium-rich sediments supplied from surrounding zones. Moreover, bauxitization is favoured by the good drainage conditions of these zones, which
are normally protected against erosion. Bardossy also indicated that, while the karstic
depression progressively grows in size due to carbonate dissolution, aluminium content
increases by leaching of the renewed external supplies.
Bauxites appear in the geological record of a great many sites in the world (Valeton,
1972). In Spain, bauxites have a karstic origin and are mainly located in the JurassicLower Cretaceous limit of the South Pyrenees, in Late Triassic sediments of the central
Catalonian Coastal Ranges and in the Lower Cretaceous of the northeastern Maestrazgo
region (Combes, 1969).
Formation of karstic bauxites has progressively increased since Paleozoic times
(Bardossy, 1981), with a notable increment during the Cenozoic probably related to an
increase in carbonate rocks. Neogene karstic bauxites constitute the fourth part of the total
existing in the world.
Climatic Geomorphology
Many bauxites can be considered as derived from leaching of old laterites. Tardy and
Roquin (1992) indicated that some aluminic laterites present two layers with gibbsite
enrichment: one near the saprolite profile base, almost in contact with the parent rock, and
the other at the profile top, near the soil surface.
Bauxitization increases with fluvial incision. It has also been observed that bauxites
show a better development along fault lines, which facilitate leaching processes. In many
cases the bauxite outcropping on an escarpment laterally wedges towards the lateritic
mass. This indicates that the bauxite does not form a continuous layer and is genetically
related to the escarpment evolution (McFarlane, 1983).
About 10% of the bauxites belong to the karstic type (Ollier and Pain, 1996). In these
cases the bauxite fills fissures, depressions, and cavities of the karstified carbonate rock.
Initially bauxites were thought to constitute insoluble residues from the dissolution of
calcareous massifs. It is difficult, however, to explain the source of important aluminium
quantities. Following Bardossy (1981), karstic depressions produced by differential
dissolution receive aluminium-rich sediments supplied from surrounding zones. Moreover, bauxitization is favoured by the good drainage conditions of these zones, which
are normally protected against erosion. Bardossy also indicated that, while the karstic
depression progressively grows in size due to carbonate dissolution, aluminium content
increases by leaching of the renewed external supplies.
Bauxites appear in the geological record of a great many sites in the world (Valeton,
1972). In Spain, bauxites have a karstic origin and are mainly located in the JurassicLower Cretaceous limit of the South Pyrenees, in Late Triassic sediments of the central
Catalonian Coastal Ranges and in the Lower Cretaceous of the northeastern Maestrazgo
region (Combes, 1969).
Formation of karstic bauxites has progressively increased since Paleozoic times
(Bardossy, 1981), with a notable increment during the Cenozoic probably related to an
increase in carbonate rocks. Neogene karstic bauxites constitute the fourth part of the total
existing in the world.