@article{fdi:010045597,
  title = {{C}hemical and physical erosion rhythms of the {W}est {A}frican {C}enozoic morphogenesis : the {A}r-39-(40) {A}r dating of supergene {K}-{M}n oxides},
  author = {{B}eauvais, {A}nicet and {R}uffet, {G}. and {H}enocque, {O}. and {C}olin, {F}abrice},
  editor = {},
  language = {{ENG}},
  abstract = {{C}hemical weathering and mechanical erosion are first-order processes of long-term tropical morphogenesis, which is still poorly deciphered for lack of time constraints. {W}e address this issue by laser probe {A}r-39-(40) {A}r dating of generations of cryptomelane [{K}1-2{M}n8{O}16, n{H}(2){O}] from the manganese ore deposit of {T}ambao in northern {B}urkina {F}aso. {T}his {M}n deposit results from the supergene weathering of carbonate and silicate {M}n protores underneath lateritic palaeolandsurfaces. {I}t consists of an upper cryptomelane-rich domain and a lower domain where pyrolusite (beta-{M}n{O}2) is the dominant {M}n oxide. {T}he oldest {A}r-39-(40) {A}r ages (59 - 45 {M}a) are obtained on surface outcrops while the youngest ones characterize deep oxidation fronts ( 3.4 - 2.9 {M}a). {A}pparent correlations of {A}r-39-(40) {A}r age groups with delta {O}-18 and eustatic curves allow definition of the different stages of morphogenesis. {P}aleocene-{E}ocene ages (59 - 45 {M}a) bracket a greenhouse period propitious to bauxitic weathering. {T}he lack of significant ages between similar to 45 and 29 {M}a characterizes a period dominated by mechanical erosion, during which detrital sediments, including lateritic materials, were accumulated in intracratonic basins allowing the exhumation of a new lateritic landsurface. {T}wo major weathering periods separated by a second erosion episode ( 24 - 18 {M}a) are also depicted at the end of {O}ligocene ( 29 - 24 {M}a) and lower to mid-{M}iocene ( 18 - 11.5 {M}a) in the upper domain, during which newly shaped land surfaces conspicuously weathered. {T}he shorter-weathering and erosion episodes recorded in the lower domain from similar to 18 to similar to 2.9 {M}a led to the final geomorphic changes that were conducive to the formation of glacis. {T}he preservation of old cryptomelane ( 59 - 45 {M}a) in the upper part of the ore deposit indicates a {C}enozoic denudation limited to the erosion of previous bauxites, and partly, of ferricretes.},
  keywords = {{BURKINA} {FASO}},
  booktitle = {},
  journal = {{J}ournal of {G}eophysical {R}esearch - {E}arth {S}urface},
  volume = {113},
  numero = {{F}4},
  pages = {art. no. {F}04007},
  ISSN = {0148-0227},
  year = {2008},
  DOI = {10.1029/2008jf000996},
  URL = {https://www.documentation.ird.fr/hor/fdi:010045597},
}