Pedogenic and lithogenic gravels as indicators of soil polygenesis in the Brazilian Cerrado

摘要: Although particles >2 mm are not considered soil material, gravels composed of resistant secondary minerals can be useful records past environments. We investigated (2–8 mm) from a Plinthic Haplustox in central Brazil order to assess their composition, fabric and genesis. Gravels were initially grouped into six macromorphological types, by mineralogical, micromorphological microprobe analyses. The results suggest that classified as pedogenic or lithopedogenic. Pedogenic comprise indurated materials include black magnetic gravels, non-magnetic red earthy gravels. Magnetic contained mostly quartz, hematite magnetite–maghemite poor kaolinite, gibbsite goethite, whereas had the same surrounding soil. Lithopedogenic fragments rocks impregnated iron (Fe), aluminium (Al) manganese (Mn) oxides, including platy shales, quartzites coarse quartz. latter two showed oxide impregnations around internal pores, shale included considerable mica, which contributed illite potassium clays and, thus, These point multiple cycles formation incorporation cemented soil, well later impregnation Fe, Mn Al oxides. Thus, conventional classification all such ‘ironstone’ is questionable, potential role indicators present environments demonstrated, deserves further investigation.