@inproceedings{fdi:010022371,
  title = {{C}lay minerals of the {E}cuadorian cangahua as products of volcanic tuff weathering},
  author = {{Q}uantin, {P}aul and {D}elaune, {M}ireille},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he {E}cuadorian {C}angahua is an indurated volcanic formation. {F}or geologists it consists of tuff resulting from induration of ash deposits. {F}or pedologists, this induration could be due to weathering products under a subarid climate. {T}he aim of this paper is to confirm the former tuff formation as well as the play of pedogenesis in the clay formation. {O}ur previous studies (chemistry, petrography, mineralogy, sedimentology) have suggested that the {C}angahua originated from pyroclastic flows of dacitic ashes. {T}he deconvolution of grain-size frequency curves (according to {L}iere et al., 1996) demonstrates the depositional process. {E}very pyroclastic event has left a composite deposit including flow and surge deposits, ash falls and hydrovolcanic products. {I}nduration of some layers, early after this deposition, could be due to former hydrothermal alteration of minute glass shards, producing amorphous matrix in the incipient {C}angahua. {N}ow, at the bottom of paleosols the {C}angahua has a matrix made of various clay minerals, which result from subsequent weathering. {I}ndeed, there is a good relationship between the nature of clay minerals and the present climatic conditions. {T}hese minerals are varying with the moisture regime from semiarid to perhumid, according to a toposequence. {W}e observe successively : at semi-arid foot-slope, predominant silica-rich clays like beidellite or poorly crystalline 2:1 clays and small amounts of opal and calcite - at semi-arid mid-slope, abundant hallysite and segregation of iron oxides - at perhumid summit, predominance of allophane and occasionally small amount of halloy site. ({R}{\'e}sum{\'e} d'auteur)},
  keywords = {{ALTERATION} ; {INDURATION} ; {ROCHE} {VOLCANIQUE} ; {ARGILE} ; {PEDOGENESE} ; {PALEOSOL} ; {FACTEUR} {CLIMATIQUE} ; {VOLCAN} ; {ETUDE} {REGIONALE} ; {EQUATEUR} ; {CANGAHUA}},
  numero = {},
  pages = {125},
  booktitle = {{E}uroclay 1999 : conference of the {E}uropean clay groups association : program with abstracts},
  year = {1999},
  URL = {https://www.documentation.ird.fr/hor/fdi:010022371},
}