02667nam a2200361 a 450000100080000000500110000800800410001910000150006024500810007526000160015630000100017250000620018252017070024465000110195165000150196265000150197765000320199265000190202465000120204365000200205565000160207565000090209165300110210065300210211165300210213265300310215365300300218465300230221465300120223765300150224965300240226465300170228815478842016-09-20       1986    bl uuuu  m   00u1 u    #d1 aMACEDO, J.  aMorphology, mineralogy, and genesis of a hydrosequence of oxisols in Brazil.  a1986.c1986  a73 p.  aThesis (Master of Science) -- Cornell University, Ithaca.  aResearch was conducted to establish the genetic relationship between soil color patterns and natural drainage characteristics in a hydrosequence of Oxisols formed in Tertiary/Quaternary sediments of the Cerrado (Savanna) Region in the Central Plateau of Brazil. The soils classify as Acrustoxs and Pilinthaquoxs in Soil Taxonomy and as Dark-Red Latosols, Red-Yellow Latosols, and Hydromorphic Laterite in the Brazilian classification scheme. In addition to standard soil classification analyses, x-ray diffraction and sodium citrate-bicarbonate-dithionite extractions were used to determine soil mineralogy. Precipitation was recorded and weekly positions of the water table at sampling sites were measured in observation wells for a period of one year. Kaolinite, gibbsite, quartz and iron oxides are the dominat minerals in all sites. Relative amounts of theses minerals show similar desilication trends with depth at all sites in the hydrosequence. Well drained soils with water tables below 3 meters had reddish hues (2.5 YR or 5 YR) reflecting and oxidizing environment and a co-dominant hematite and goethite iron mineralogy. The upper organic rich solum in sites with seasonally high water tables (&lt2m) had yellowish hues (10 YR or 7.5 YR) and dominantly goethitic iron mineralogy. In the deeper perennially saturated zones of all profiles the matrix color has reddish hues (2.5 YR or 10R) and a dominantly hematitic iron mineralogy. Stratigraphic, geomorphic, and pedogenic evidence supports the hypothesis that the observed soil colors and corresponding differences in iron mineralogy are a pedogenic adjustment to change in the hydrology of these soils brought about by landscape evolution.  aBrazil  aFerralsols  amineralogy  asoil morphological features  asoil sequences  aCerrado  aGênese do Solo  aMineralogia  aSolo  aBrasil  aDark-red latosol  aDistrito Federal  aLatossolo vermelho-amarelo  aLatossolo vermelho-escuro  aMorfologia do solo  aOxisolo  aPlanaltina  aRed-yellow latossol  aSoil genesis