Pomel, S. and Salomon, J. N. (1996): Les Croutes volcaniques aux Canaries Volcanic crusts in the Canary Islands


Pomel, S.
Universite de Bordeaux, Laboratoire Environnement, Talence, France

Salomon, J. N.
Universite Michel de Montaigne-Bordeaux III, Talence, France

Les Croutes volcaniques aux Canaries Volcanic crusts in the Canary Islands
In: Bourrouilh-Le Jan, Francoise G., Carbonates intertropicaux Tropical carbonates
Societe Geologique de France, Paris, France
Encrusted over spaces occupy huge areas all over the world, particularly in arid and semiarid regions. This wide-scale geographical distribution results in a varied range of situations that are not always fully understood. Although a great many calcretes are distributed in the landscape from complex morphopedological processes evoked by various schools (lateral drifts, neoformation, evaporation or biological processes, pedological redistribution and so on), the question of calcium input and thus that of the genesis of carbonates remains. In the Canary Islands these different processes often provide a fairly good explanation for certain microfacies of the crusts but not for the precise distribution of carbonates in the catena. The authors put forward an aeolo-volcanic explanation and for the Canary Islands a mainly pedological evolution (basalt weathering). In fact the terms of "caliche" in the Canary Islands cover very varied formations. The variety of "caliches" hardly conceals the fundamental part played by volcanism in the genesis of the crusting over. A great many calcretes even if they derive from modification of volcanic rocks and have been subjected to an important remobilization of carbonates by pedogenesis, mark out the vitroclastic dustings. Frequent associations of vertisoils and palaeo-vertisoils with multiple carbonated horizons mark out the explosive functioning of the strato-volcanoes during the massive providing of volcanic smectites (beidellites and/or hydrated amphiboles). The silico-carbonated encrustings of La Palma or La Gomera are linked to the formation of their large trachy-phonolitic calderas in the Miocene. This is also the case of El Hierro and Tenerife in the Pliocene and the Quaternary. The Canary Islands thus supply exceptional incidences of carbonated (or gypseous) crusts related to the direct volcanic consequences buried in the elastic colluvium and products of slopes which accompany the explosive functioning and erosion of the large depressions in the sides of basaltic strato-volcanoes. The theory of volcanic wind-borne contributions appears strenghtened to account for the genesis of calcretes. Among the stated arguments, it is demonstrated that calcretes can mould topographies, that carbonates may have cryptocristalline petrographic facies or contain plentiful dated volcanic tracers (tephra, allophanes and zeoliths).
Coverage:Geographic coordinates:
West:-80.0000East: 20.0000

Sedimentary petrology; Atlantic Ocean; Atlantic Ocean Islands; calcrete; calderas; caliche; Canary Islands; carbonate rocks; catenas; Cenozoic; Deep Sea Drilling Project; evaporation; igneous rocks; microfacies; Miocene; Neogene; paleoclimatology; paleosols; Phanerozoic; phonolites; Pliocene; Quaternary; sedimentary rocks; soils; spatial distribution; stratovolcanoes; Tertiary; trachytes; upper Tertiary; Vertisols; volcanic features; volcanic rocks; volcanoes; weathering; wind transport;