Abstract
Rock samples representing different soil parent materials from the Jurassic, Cretaceous and Tertiary periods in eastern Saudi Arabia were investigated for their mineralogical and chemical properties. Samples from five soil profiles found on these rocks also were studied. Palygorskite was found to be the dominant mineral in the clay fraction of the Tertiary and upper Cretaceous sediments. Some shales of Tertiary origin contained mainly palygorskite with minor amounts of gypsum and soluble salts. Palygorskite was not found in any sediments of the early lower Cretaceous and Jurassic periods, and kaolinite was the dominant mineral in the clay fraction of those sediments. Soils associated with Jurassic limestone near the Riyadh area also showed a predominance of kaolinite in their clay fractions. However, the clay fractions of the soils found on Tertiary sediments in the eastern part of the country were dominated by palygorskite. The presence of palygorskite in the soils paralleled its presence in the parent materials or the rocks exposed in the area. Eolian transport of palygorskite was found to be a factor for the occurrence of palygorskite in the soils. Thus, the major portion of the soil palygorskite probably originated from the Tertiary sediments in eastern Saudi Arabia.