SOIL CATENA VARIATION ALONG AN ALPINE CLIMATIC TRANSECT, NORTHERN PERUVIAN ANDES

Morphological and chemical properties of soils developed on end moraines of mostly quartzitic and granitic composition in the puna region of the northern Peruvian Andes vary with slope position and climate. Soil development was assessed on two catenas of similar age range (8-12 ka) in two different precipitation zones at summit, backslope, and footslope positions. Soil properties that show trends downslope and with increased rainfall are: greater clay content, greater organic-carbon content, and greater pedogenic Fe content. In addition, pH is lower in the higher rainfall area. Eolian material (mixed loess), forms the surface layer (A horizon) and may be responsible for the remarkable slope stability in the area. It is suggested that mixed loess provided material for chemical alteration and translocation of clay and Fe vertically and downslope in quartz-rich parent materials. Soil data suggest that the amount of climate change during the Holocene is limited; it is doubtful if the climate at the wetter end of the transect ever existed at the drier end.