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Soil Science Society of America Journal

V.57,No.4

(July-August 1993)

P.1041-1050

Reprinted from the Soil Society of America Journal

Aridisols,Soil -- types -- polyentic,Soil micromorphology

Soils in arid regions are often polygenetically related to climatic variation.On a dissected alluvial fan in the western Mojave Desert, a Typic Durorthid (loamy,mixed,thermic,shallow;Alko series)and two Typic Haplargids (fin-loamy,mixed,thermic,Neuralia and Garlock series) were selected for micromorphological investigation to determine the sequence of pedogenic events.The micromorphology of pedogenic silica,carbonate and clay is described for duripans,duric horizons (Btqk),and underlying buried Bt horizons in these soils.In the Alko and Neuralia soils,rodent bioturbation has transported subsurface calcareous fragments, thereby enriching the soil surface with silica and CaCO3.These fragments are not completely removed from the surface by leaching under the present - day climate.Clay illuviation and silicification occurred simultaneously in the lower duripan (40-150cm)of the Alko,with subsequent accumulation of CaCo3 in seams and root channels.Silicification of the Btqk and buried Bt horizons in the Neuralia and Garlock soils occurred after clay illuviation.The complete cementation of the lower duripan in the Alko soil has apparently isolated the buried Bt,but the buried Bt horizons in the Neuralia and Garlock soils have undergone further calcification and silicfication.We speculate that the polygenesis of soils in the study area is related to climatic fluctuations since the mid-Pleistocene and to bioturbation of surface horizons.Development of carbonate-free argillic horizons probably occurred during pluvial periods,whereas calcification occurred during drier periods.Silicification appears to have been contemp..

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Ghasemi

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