HR: 1340h
AN: B23B-1268    [Abstracts]
TI: Mineral Occurrence, Translocation, and Weathering in Soils Developed on Four Types of Carbonate and Non-carbonate Alluvial Fan Deposits in Mojave Desert, Southeastern California
AU: * Deng, Y
EM: ydeng@ag.tamu.edu
AF: Texas A&M University, Department of Soil and Crop Sciences, College Station, TX 77843, United States
AU: McDonald, E V
EM: Eric.McDonald@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, United States
AB: Soil geomorphology and mineralogy can reveal important clues about Quaternary climate change and geochemical process occurring in desert soils. We investigated (1) the mineral transformation in desert soils developed on four types of alluvial fans (carbonate and non-carbonate) under the same conditions of climate and landscape evolution; and (2) the effects of age, parent materials, and eolian processes on the transformation and translocation of the minerals. Four types of alluvial-fan deposits along the Providence Mountains piedmonts, Mojave Desert, southeastern California, USA were studied: (1) carbonate rocks, primarily limestone and marble (LS), (2) fine-grained rhyodacite and rhyolitic tuff mixed with plutonic and carbonate rocks (VX), (3) fine- to coarse- grained mixed plutonic (PM) rocks, and (4) coarse-grained quartz monzonite (QM). These juxtaposed fan deposits are physically correlated in a small area (about 20 km by 15 km) and experienced the same climatic changes in the late Pleistocene and Holocene. The soils show characteristic mineral compositions of arid/semiarid soils: calcite is present in nearly all of the samples, and a few of the oldest soils contain gypsum and soluble salts. Parent material has profound influence on clay mineral composition of the soils: (1) talc were observed only in soils developed on the volcanic mixture fan deposits, and talc occurs in all horizons; (2) palygorskite occur mainly in the petrocalcic (Bkm) of old soils developed on the LS and VX fan deposits, indicating pedogenic origin; (3) chlorite was observed mainly in soils developed on VX fan deposits (all ages) and on some LS deposits, but it is absent in soils developed on PM and QM fan deposits; and (4) vermiculite was common throughout soils developed on plutonic rock fan deposits. These mineralogical differences suggest that minerals in the soils are primarily inherited from their parent materials and that mineral weathering in this area was weak. Except the abundance of palygorskite, soils developed on alluvial fans with different ages (4,000 to 200,000 yrs old) did not show other distinct mineralogy difference as a function of age or soil development, which supports the weak weathering of the soils. The results suggest that the clays in the argillic horizons are primarily derived from the accumulation of desert dust, and with time, are translocated into subsoil horizons. The pedogenic accumulation of dust is a soil-geomorphic process common to the Mojave Desert, as well as other deserts in the world.
DE: 0486 Soils/pedology (1865)
DE: 1865 Soils (0486)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting