W. D. Nettleton, J. E. Witty, R. E. Nelson, J. W. Hawley1
1Asst. Principal Soil Correlator. USDA, SCS, Upper Darby, Pa.; Geologist, USDA, SCS, Lubbock, Texas, respectively.; Research Soil Scientist, USDA, SCS, Riverside, Calif.
Tóm tắt
AbstractWe studied soils and landscapes in the southwestern part of the Lake Lahontan drainage basin in Nevada and soils on alluvial fans near Phoenix and Willcox, Arizona and Mojave, California. The youngest surface is less than 12,000 YBP (years before present), the oldest is pre‐Wisconsin in age. Typic Torripsamments are on surfaces younger than 12,000 YBP, finer textured Haplargids and Paleargids are on surfaces older than 12,000 YBP. The volume of clay skins in a sandy family of Xeralfic Haplargids on a late Wisconsin age, dune‐sand surface is approximately equal to the increase of clay in its B horizon, whereas clay skins are mostly lacking in the fine‐textured Haplargids and Paleargids formed in sandy alluvium. Both the distribution of quartz and total silica in the sand + silt and the distribution of volcanic fragments in the very fine sand show that the A horizons of the finer textured Haplargids and the Paleargid are as weathered as, or more weathered, than their B horizons. This is evidence that the B horizons of Argids were formed at least in part by translocation of clay. Accumulation of total Al2O3 and Fe2O3 in these argillic horizons is more direct evidence that clay translocation occurred. The older Argids have clay maxima below the calculated depth of wetting in most years. These clay maxima are near the depth of wetting expected once or twice each 100 years in the older Argids, but the present climate does not seem adequate to have produced the soils in the time involved. Rather these older Argids are probably products of moister Plestocene climates.
