Chemical input-output analyses were used to evaluate the rate of rock weathering and soil development on a granitic inselberg of the Dragoon Mountains in southeastern Arizona. Soil genesis relationships were investigated through field and laboratory study of the soil profile, parent rock, microclimate and vegetation, on different catena positions and hillside aspects. Precipitation and runoff water qualities were determined, with increased summer acidity. Precipitation volume was estimated by extrapolating data from a nearby recording station. Runoff volume was estimated by the U.S.D.A.-S.C.S. Curve Number Method (1972). These data enabled the quantitative determination of cationic solution loss. The indicated decreasing order of cation mobility is calcium, sodium, potassium and magnesium. Cations of higher mobility are relatively depleted in the hillcrest soils, while transported to the footslope or beyond. Calcium, and to a lesser extent sodium, have experienced more extensive off-site removal. Differences resulting from the transformation of parent material to soil were analyzed by field morphology, X-ray analysis, laser light-scattering particle size analysis, and chemical analyses. The study site was surveyed, mapped and the spatial arrangement of soil taxa and their compositional variation were studied. Nearly all pedons on the crest or transport slope are Lithic Ustic Torriorthents; whereas footslope soils show greater development, as exemplified by the occurrence of various Haplargids, Haplustolls and Argiustolls. Weathering rates were calculated using a methodology similar to that of F. W. Barth (1961). Potassium and magnesium provided the most reasonable data of 350 and 430 Kg ha⁻¹ yr⁻¹, respectively. (equivalent to 13.5 and 16.5 mm of rock weathered per 1000 years). Two serrated projectile points were found inbedded on the clayey soil surface of an adjacent ancient pond site. These artifacts resemble another projectile point found in southeastern Arizona which has been radiocarbon dated ~7,000 yr B.P. A minimum age for the pond and immediate surrounding topography is suggested to correspond with the end of the western subhumid pluvial period. The assessment of the geochemical budget provided a valuable framework for quantification of the various processes which interactively determine the rates of weathering and soil formation.

Important pedogenic processes of soils formed on dolomitic limestones are affected by the degree of in-situ weathering of the underlying bedrock. Decalcification and silicate clay illuviation of Haplustalfs and Calciustolls of the Colorado Plateau in northwestern Arizona results from the establishment of effective porosity in the parent rock. The underlying carbonate strata, the Kaibab Formation, are a complex limestone-dolomite-chert marine sediment of Permian age. Diagenetic processes have modified the initial porosity present at the time the sediment was deposited. Pleistocene meteoric waters, percolating downward, have resulted in the solutioning and partial removal of the calcium carbonate and the establishment of a porous dolomitic framework. Under these conditions, soils forming in residuum are able to decalcify and to form argillic horizons. However, in more resistant limestones, compaction during burial has resulted in a nonporous micrite which retards calcite removal by meteoric waters. Under these conditions, soil profiles maintain a high CaCO₃ content and silicate clay illuviation does not occur. Micaceous clay minerals of residual origin are converted to montmorillonite in the Alfisols. A probable sequence of events for this transformation to occur is: (1) the removal of calcite from the dolomitic limestone bedrock and the formation of a dolomitic framework, (2) the slow dissolution of dolomite and release of Mg⁺⁺ into solution, (3) the incorporation of Mg⁺⁺ into the octahedral layer of the mica and the release of K⁺ from the mica interlayer position, and (4) the illuviation of montmorillonite to form the argillic horizon. Eolian dust is also important to soil genesis on the Colorado Plateau. In particular, quartz in the coarse silt fraction (31-44 um) and quartz and biotite in the very fine and fine silt fractions (2.0-16 um). Two alluvial soils of Pleistocene age shows important morphological differences. Thick carbonate accumulations of ground water origin are present in the older soil. The effects of the Pleistocene-Holocene climatic change on this area are: (1) modification of karst topographic features, (2) aggradation of valley bottoms, and (3) the influence of Holocene slope wash Pleistocene soil properties such as calcite, dolomite and organic matter.

No description available.

The objective of this study was to determine whether the properties of four soils of the Silverbell Desert Biome could be attributed solely to the parent material or alternately reflect the nature of contributions, if any, from eolian dust. The Anklam, Lajitas and Chimenea soils, classified as fine-loamy, mixed, thermic Lithic Haplargids and the Greyeagle (coarse-loamy, mixed, thermic, Lithic Torriorthent) soil formed an andesite, basalt, granite and basalt, respectively. They occur on gently sloping, stable terrain in Pima County, Arizona. The four soils were studied through field descriptions, particle size analysis, mineralogical analyses of light and heavy sand fractions and clay mineral identification. The light mineral fraction of all four soils is directly affected by the parent material and is influenced much less, if at all by eolian activities due to the larger particle sizes. It is concluded that the genesis of soils was influenced by both the underlying rock and the input of eolian particulates. (Abstract shortened with permission of author.)

No description available.

No description available.