Self-organization in chemical lateritic weathering

Abstract Ferruginous laterites consist of different superposed horizons characterized by their mineralogical and structural composition. Climatic changes are foremost among the parameters used to explain variations of mineralogy and structures. However, several types of structures can be explained as the spontaneous and autonomous change of the geochemical soil system without the intervention of external factors such as climate or tectonics. Two examples illustrate this self-organization of lateritic horizons: formation of a ferruginous nodular horizon and formation of a conglomeratic iron crust. Self-organization results from reaction-transfer feedbacks between permanently precipitated and dissolved minerals and continuously percolating solutions allowing the geochemical soil system to be in constant search of equilibrium.

[1]  D. Nahon,et al.  Petrological and geochemical differentiation of lateritic iron crust profiles , 1986 .

[2]  D. Nahon,et al.  The epigenetic replacement of kaolinite by hematite in laterite — petrographic evidence and the mechanisms involved , 1986 .

[3]  V. Farmer.  The Infrared spectra of minerals , 1974 .

[4]  Enrique Merino,et al.  Geochemical self-organization I; reaction-transport feedbacks and modeling approach , 1987 .

[5]  Y. Tardy,et al.  Recherches sur les mécanismes du concrétionnement. Coefficients d'activité des ions, solubilité des sels et de la silice dans les pores de petite taille , 1983 .

[6]  D. N. Hinckley.  Variability in “crystallinity” Values among the Kaolin Deposits of the Coastal Plain of Georgia and South Carolina , 1962 .

[7]  F. Trolard,et al.  The stabilities of gibbsite, boehmite, aluminous goethites and aluminous hematites in bauxites, ferricretes and laterites as a function of water activity, temperature and particle size , 1987 .

[8]  H. Paquet,et al.  Genèse des phosphates alumineux à partir des sédiments argilo-phosphatés du Tertiaire de Lam-Lam (Sénégal). Suite minéralogique. Permanences et changements de structures , 1977 .

[9]  D. Nahon,et al.  MINERALOGY, PETROGRAPHY AND STRUCTURES OF IRON CRUSTS (FERRICRETES) DEVELOPED ON SANDSTONES IN THE WESTERN PART OF SENEGAL , 1977 .

[10]  D. Nahon,et al.  Geochemistry of laterites, stability of Al-goethite, Al-hematite, and Fe (super 3+) -kaolinite in bauxites and ferricretes; an approach to the mechanism of concretion formation , 1985 .