HR: 0800h
AN: B41D-0223    [Abstracts]
TI: Eolian Additions to Late Quaternary Alpine Soils, Indian Peaks Wilderness Area, Colorado Front Range
AU: * Muhs, D R
EM: dmuhs@usgs.gov
AF: U.S. Geological Survey, MS 980, Box 25046, Federal Center, Denver, CO 80225 United States
AU: Benedict, J B
B41D-0223 AF: Center for Mountain Archeology, 8297 Overland Road, Ward, CO 80481 United States
AB: Surface horizons of many alpine soils on Quaternary deposits in high-mountain settings are enriched in silt. The origin of these particles has been debated, particularly in the Rocky Mountain region of North America. The most common explanations are frost shattering of coarser particles and eolian additions from distant sources. We studied alpine soil A horizons on moraines of late-glacial age (about 11,000 to 10,000 radiocarbon years old) in the Colorado Front Range. Surface horizons of soils on these moraines are enriched in silt and have a particle size distribution that resembles loess and dust deposits found elsewhere. The compositions of sand and silt fractions in the soils were compared to possible local source rocks, using immobile trace elements Ti, Nb, Zr, Ce, and Y. The sand fractions of soils have a wide range of trace element ratios, similar to the range of values in the local biotite gneiss bedrock. In contrast, silt fractions have narrower ranges of trace element ratios that do not overlap the range of these ratios in biotite gneiss. The particle size and geochemical results support an interpretation that silts in these soils were derived from airborne dust. Based on similar geochemistry, eolian silts were most likely derived from distant sources, such as the semiarid North Park and Middle Park basins to the west. Although eolian silt additions may be an ongoing process, we hypothesize that much of the eolian influx to soils of the Front Range occurred during an early-to-mid-Holocene warm and dry period, when sediment availability in semiarid source basins was at a maximum.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0486 Soils/pedology (1865)
DE: 0718 Tundra (9315)
SC: Biogeosciences [B]
MN: Fall Meeting 2005