Soil Genesis in a Developmental Sequence of Soils Formed in Sillimanite Mica Schist Residuum

Abstract

AbstractDystochrepts formed in mica schist residuum occur on steeply sloping sideslopes, whereas associated Hapludults are found on gently sloping ridgetops in the Piedmont province of Georgia. In this study, morphological, physical, chemical, and mineralogical properties of Dystrochrepts and associated Hapludults were examined to determine the influence of weathering intensity differences within the pedon and across the Dystrochrept → Hapludult developmental sequence. More intense weathering at the soil surface has resulted in higher exchangeable Al contents, lower pH values, and a relative accumulation of total Si, quartz, sillimanite, opaque minerals, and clay‐sized mica and vermiculite. In contrast, biotite was more abundant at depth. Total Al was closely related to clay distribution within the pedon. Less intense weathering in the Dystrochrepts, apparently related to shorter development time, has led to coarser textured sola with higher base saturations, higher total Mg, K, and Na contents, and a greater abundance of fine sand‐sized biotite and K‐feldspar. Quartz in the fine sand fraction was concentrated in the Hapludult. Kaolinite was the dominant clay mineral in the Hapludult. Regularly interstratified mica‐vermiculite was identified in subsurface horizons of the Dystrochrept and is believed to be a transitory intermediate in the transformation of mica to vermiculite.