Subdivision of glacial deposits in southeastern Peru based on pedogenic development and radiometric ages

The Cordillera Vilcanota and Quelccaya Ice Cap region of southern Peru (13 degrees 30'-14 degrees 00'S; 70 degrees 40'-71 degrees 25'W) contains a det ailed record of late Quaternary glaciation in the tropical Andes, Quantific ation of soil development on 19 moraine crests and radiocarbon ages are use d to reconstruct the glacial history. Secondary iron and day increase linea rly in Quelccaya soils and clay accumulates at a linear rate in Vilcanota s oils, which may reflect the semicontinuous addition of eolian dust enriched in secondary iron to all soils. In contrast, logarithmic rates of iron bui ldup in soils in the Cordillera Vilcanota reflect chemical weathering; high concentrations of secondary iron in Vilcanota tills may mask the role of e olian input to these soils. Soil-age estimates from extrapolation of field and laboratory data suggest that the most extensive late Quaternary glaciat ion occurred >70,000 yr B.P. This provides one of the first semiquantitativ e age estimates for maximum ice extent in southern Peru and is supported by a minimum-limiting age of similar to 41,520 C-14 yr B.P. A late glacial re advance culminated similar to 16,650 cal yr B.P. in the Cordillera Vilcanot a, Following rapid deglaciation of unknown extent, an advance of the Quelcc aya Ice Cap occurred between similar to 13,090 and 12,800 cal yr B.P., whic h coincides approximately with the onset of the Younger Dryas cooling in th e North Atlantic region. Moraines deposited <394 cal yr B.P. in the Cordill era Vilcanota and <300 cal yr B.P. on the west side of the Quelccaya Ice Ca p correlate with Little Ice Age moraines of other regions. (C) 2001 Univers ity or Washington.