@article{fdi:010075337,
  title = {{M}ineralogy and genesis of smectites in an alkaline-saline environment of {P}antanal wetland, {B}razil},
  author = {{F}urquim, {S}. {A}. {C}. and {G}raham, {R}. {C}. and {B}arbi{\'e}ro, {L}aurent and {N}eto, {J}. {P}. {D}. and {V}alles, {V}.},
  editor = {},
  language = {{ENG}},
  abstract = {{S}mectite formation in alkaline-saline environments has been attributed to direct precipitation from solution and/or transformation from precursor minerals, but these mechanisms are not universally agreed upon in the literature. {T}he objective of this work was to investigate the mineralogy of smectites in the soils surrounding a representative alkaline-saline lake of {N}hecolandia, a sub-region of the {P}antanal wetland, {B}razil, and then to identify the mechanisms of their formation. {S}oils were sampled along a toposequence and analyzed by {X}-ray diffraction, transmission electron microscopy-energy dispersive {X}-ray analysis, and inductively coupled plasma-mass spectrometry. {W}ater was collected along a transect involving the studied toposequence and equilibrium diagrams were calculated using the databases {PHREEQC} and {AQUA}. {T}he fine-clay fraction is dominated by smectite, mica, and kaolinite. {S}mectites are concentrated at two places in the toposequence: an upper zone, which includes the soil horizons rarely reached by the lake-level variation; and a lower zone, which includes the surface horizon within the area of seasonal lake-level variation. {W}ithin the upper zone, the smectite is dioctahedral, rich in {A}l and {F}e, and is classified as ferribeidellite. {T}his phase is interstratified with mica and vermiculite and has an {F}e content similar to that of the mica identified. {T}hese characteristics suggest that the ferribeidellite originates from transformation of micas and that vermiculite is an intermediate phase in this transformation. {W}ithin the lower zone, smectites are dominantly trioctahedral, {M}g-rich, and are saponitic and stevensitic minerals. {I}n addition, samples enriched in these minerals have much smaller rare-earth element ({REE}) contents than other soil samples. {T}he water chemistry shows a geochemical control of {M}g and saturation with respect to {M}g-smectites in the more saline waters. {T}he {REE} contents, water chemistry, and the presence of {M}g-smectite where maximum evaporation is expected, suggest that saponitic and stevensitic minerals originate by chemical precipitation from the water column of the alkaline-saline lake.},
  keywords = {{C}hemical {P}recipitation ; {F}erribeidellite ; {M}g-smectite ; {M}ica-smectite ; lnterstratification ; {N}eoformation. {T}ransformation ; {T}rioctahedral ; {S}mectite ; {S}aline {L}ake ; {BRESIL}},
  booktitle = {},
  journal = {{C}lays and {C}lay {M}inerals},
  volume = {56},
  numero = {5},
  pages = {579--595},
  ISSN = {0009-8604},
  year = {2008},
  DOI = {10.1346/ccmn.2008.0560511},
  URL = {https://www.documentation.ird.fr/hor/fdi:010075337},
}