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Parent Material Uniformity and Origin of Silty Soils in Northwest Arkansas Based on Zirconium-Titanium Contents¹

ABSTRACT

Uniformity of parent material studies were made of 15 soils overlying various geologic materials, utilizing petrographic and X-ray spectographic techniques. Zr and Ti contents were used as tests for a "loess" versus a "residual silt" hypothesis for the origin of silty soils in northwestern Arkansas. The lack of significant deviations with depth in Zr and Ti contents and ratios points to an absence of lithologic discontinuities in soils suspected of having an upper loess parent material. It is concluded that these soils are formed in local materials and not from extra-regional loess. It is proposed that prolonged weathering of local rocks together with reworking by mass movements, water, and wind on a local basis has resulted in a rather homogeneous regolith on the older gently sloping landscapes over cherty limestones and siltstones. The local nature of the soil parent materials is also indicated by the fact that Zr and Ti contents in the very fine sands were found to be related to underlying rocks being highest (ZrO₂, 0.30%; TiO₂, 0.26%) in soils over sandstone and lowest (ZrO₂, 0.03% TiO₂, 0.10%) in soils over cherty limestone. Zr was most abundant in coarse silts except for two soils over sandstone in which it was most abundant in the very fine sands. Ti increased as particle size decreased. In several soils Ti was present as leucoxene coatings on quartz and chert grains of very fine sand size. This indicates the probable translocation of Ti in soils and its general unsuitability as a stable constituent in soil genesis studies.

¹ Contribution from the Department of Agronomy, University of Arkansas, Fayetteville. Approved for publication by the Director of the Arkansas Agr. Exp. Sta. Part of a thesis submitted by the senior author in partial fulfillment of the requirements of the M. S. degree at the University of Arkansas. Presented before Div. S-5, Soil Science Society of America, Still-water, Okla., Aug. 25, 1966.

² Former Research Assistant, and Associate Professor of Agronomy, respectively, Department of Agronomy, University of Arkansas. Senior author now Graduate Research Assistant in Soils, University of Wisconsin.

Received for publication January 30, 1967. Accepted for publication November 21, 1967.