Pedogenesis on the Edwards Plateau, Texas: II. Formation and Occurrence of Diagnostic Subsurface Horizons in a Climosequence

Abstract

AbstractFollowing reconnaissance efforts to minimize differences in parent materials, 15 pedons were sampled across the Edwards Plateau of Texas, which spans a pronounced moisture gradient. Care was taken to minimize differences in topography by choosing sites on relatively stable landscape positions. Statistically significant positive relationships exist between depth to bedrock or petrocalcic horizon and Thornthwaite's P‐E index. Negative relationships occur between carbonate contents and this index. Petrocalcic horizons are common and most strongly expressed in the dry western part of the study area, while argillic horizons are observed in the more humid eastern portion. High shrink swell activity in the argillic horizons (coefficient of linear extensibility [COLE] values 0.09–0.23) caused difficulty in distinguishing illuvial clay from stress oriented clay, both in the field and in thin section. Well‐oriented illuvial clay was best preserved within interconnected pores of sand and gravel size chert fragments.