Stratification of parent material in European volcanic and related soils studied by laser-diffraction grain-sizing and chemical analysis

Sedimentary stratification identified by field descriptions of 12 soils derived wholly or partly from volcanic materials was compared with results obtained by chemical analyses (contents and ratios of lithogenic elements, contents of heavy metals) and detailed grain-size data after removal of organic matter and amorphous fractions. The finest sedimentary stratification was indicated by cluster analysis of ratios of lithogenic elements and by the grain-size analyses. Sedimentary stratification in the field is difficult to determine or describe when (1) the deposits are strongly weathered, (2) soil horizon boundaries coincide with stratification boundaries or (3) stratification is very fine. Nevertheless, field descriptions are a reasonably good way of differentiating parent materials, though they often underestimate the number of sedimentary layers. (C) 2003 Elsevier B.V. All rights reserved

Aluminium fractionation of European volcanic soils by selective dissolution techniques

Several selective dissolution methods were used to differentiate Al forms in 12 soils formed from volcanic materials (64 andic, vitric and organic horizons) in Iceland, Azores (Portugal), Tenerife (Spain) and Italy. The soils differ in many properties because of differences in parent materials, climatic conditions, soil age and history of land use. 'Inorganic' fractions of Al were characterized using pyrophosphate (Al-p), acid oxalate (Al-o) and cold NaOH (Al-n) extractions. The difference in Al-o-Al-p, and Si extracted using acid oxalate, shows important differences among soils from different sources: allophane is richer in alumina in the Andosols from Azores and Tenerife than in those from Iceland and Italy. Cold NaOH generally extracted the same quantity of Al as acid oxalate, but in the soils from Tenerife Al-n exceeds Al-o, indicating the presence of gibbsite or poorly ordered halloysite. To characterize the Al bonded to the organic matter fraction, extractions with pyrophosphate, CuCl2 and LaCl3 were used. Except in one soil from Tenerife (N10), CuCl2 extracted less Al than pyrophosphate. In organic-rich mineral horizons, Al-LA, Al-Cu and Al-p increase with organic carbon content. Using unbuffered KCl and LaCl3, the amount of Al extracted increased with decreasing soil pH, but there was no similar relationship with unbuffered CuCl2. The general sequence of efficiency of the extractants was Al-p>Al-Cu>Al(La)greater than or equal toAl(K) in organic matter-rich horizons. Al-Cu constituted 30% of Al-p in all soils, indicating that CuCl2 extracts a very specific Al fraction. Al-p and Al-Cu are positively related to organic C. Al-p/Al-o, and Al-p-Al-Cu in andic horizons also increase with organic C. Phosphate retention and pH in NaF were related to Al-o and Al-n. The soils of Iceland have larger P retention than the others, and vitric horizons from Tenerife have higher pH in NaF and smaller Al pools than the other soils. For many horizons, there is a strong relationship between Al-Cu and components that determine soil CEC (organic matter and allophane), suggesting a possible action of CuCl2 on noncrystalline alummosilicates. This should be taken into account if CuCl2 is used to estimate Al in humus complexes. (C) 2003 Elsevier B.V. All rights reserved

Importance de la fersiallitisation sur les basaltes miocènes du Massif Central : principales caractéristiques de cette pédogenèse

A pedogenesis of f ersial litic type is developed, by generalized way, on basalts of the Massif Central, in the Middle and Upper Miocene , between 21 and 6,5 millions of years. Its main characteristics can been summarized as follows : ochre or red in color in the whole profile, intense désintégration of parent rock, .occurrence of 2/1 and 1/1 clays in < 2 yx phases, and more or less wheathered primary minerals in the 2-50 p fraction, saturation higher than 50 % in all horizons, almost complete leaching of cations Ca, Mg, К and Na. These results exclude their connection with the ferrallitic domain and are compatible with an evo¬ lution of fersiallitic type.Une pédogénèse de type fersialitique s'est développée d'une manière généralisée sur les basaltes du Massif Central au Miocène moyen et terminal entre 21 et 6,5 millions d'années. Ses caractéristiques essentielles sont les suivantes : teinte ocre à rouge sur l'ensemble des profils, ameublissement plus ou moins intense de la roche mère, présence d'argiles 2/1 et 1/1 dans les phases < 2 pm. et de minéraux primaires plus ou moins altérés dans les fractions 2-50pm taux de saturation supérieur à 50 % dans tous les horizons, évacuation quasi totale des cations Ca, Mg, К et Na. Ces données excluent l'appartenance de ces sols au domaine ferrallitique et sont compatibles avec une évolution fersiallitique .Chesworth W., Dejou Jean, De Kimpe C., Macias -Vasquez F., Cantagrel J.M., Larroque P., Garcia-Paz C., Garcia-Rodeja E. Importance de la fersiallitisation sur les basaltes miocènes du Massif Central : principales caractéristiques de cette pédogenèse. In: Pétrologie des altérations et des sols. Vol. III : Pédologie. Pétrologie appliquée aux substances utiles. Colloque international du CNRS, Paris 4-7 juillet 1983. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1983. pp. 53-62. (Sciences Géologiques. Mémoire, 73