HR: 1340h
AN: PP33B-1279    [Abstracts]
TI: Cosmogenic ¹⁰Be Dating of Early and Latest Holocene Moraines on Nevado Salcantay in the Southern Peruvian Andes
AU: * Licciardi, J M
EM: joe.licciardi@unh.edu
AF: University of New Hampshire, Department of Earth Sciences, Durham, NH 03824, United States
AU: Schaefer, J M
EM: schaefer@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Division of Geochemistry, Palisades, NY 10964, United States
AU: Lund, D C
EM: dlund@gps.caltech.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109, United States
AB: A two-fold sequence of nested lateral and end moraines was mapped in a glacial trough emanating from the southwest flank of Nevado Salcantay (6271 m; ~13°S latitude), the highest peak in the Cordillera Vilcabamba of southern Peru. The field area is situated 25 km due south of the archaeological site of Machu Picchu. Outer and inner moraines in the sequence were deposited by valley glaciers that terminated ~5 km and ~3 km, respectively, from their headwall on the Salcantay summit massif. Cosmogenic ¹⁰Be surface exposure dating of granitic boulders sampled on the Salcantay moraines is underway and has provided the first numerical ages for these deposits. Initial results indicate ages of 8.1 ± 0.1 ¹⁰Be ka for the outer moraine and 200 ± 20 ¹⁰Be years for the sharp-crested inner moraine. These ages are derived using the CRONUS-Earth ¹⁰Be exposure age calculator (version 2.0) and expressed with respect to the Lal- Stone production rate scaling scheme using the standard atmosphere. The outer and inner moraine ages correspond to glacial events during the early and latest Holocene, respectively. Further ¹⁰Be dating of the mapped moraines and similar deposits observed in adjacent drainages on Nevado Salcantay is anticipated to yield a high-resolution chronology of valley glaciation in this segment of the southern Peruvian Andes. The new results bridge an important gap between existing Andean glacier records to the north and south, and complement available ice core and lacustrine paleoclimate records in the vicinity, thereby expanding spatial and temporal coverage for identifying patterns of Holocene climate change in the tropical Andes. Notably, the inner moraine age correlates with the timing of the Little Ice Age as defined in northern mid- and high latitude glacier records, and suggests considerable expansion of valley glaciers in the southern Peruvian Andes during this climatic minimum. Apart from their paleoclimatic significance, the initial results also demonstrate the utility of ¹⁰Be exposure dating for historical surface deposits.
DE: 0720 Glaciers
DE: 1105 Quaternary geochronology
DE: 1130 Geomorphological geochronology
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting