COLLUVIAL SOIL PARENT MATERIAL RELATIONSHIPS IN THE RIDGE AND VALLEY PHYSIOGRAPHIC PROVINCE OF PENNSYLVANIA1

Abstract

We studied seven soil pedons developed in colluvium and located at the base of four primary ridges in Pennsylvania. In these footslope positions much of the colluvium consists of an upper brown layer (UBn layer) overlying a buried red layer (Rd layer). Landforms present at the study areas indicate that the UBn layer accumulated as stone-banked solifluction lobes or benches that flowed over the Rd layer during a periglacial environment. The UBn layer has 10YR to 7.5YR hues, is generally 1 to 3 m thick, and can be separated into sublayers. The Rd layer has mostly 5YR hues and is 1 to 2+ m thick. The color of the Rd layer is related to weathering rather than lithology. Beneath the colluvium is a thin lower brown layer (LBn layer) of residuum over bedrock. These layers represent a distinctive parent material sequence for recent soil development. Recognizing the nature of this sequence leads to a better understanding of pedogenesis of these soils. Color, texture, and the distribution of rock fragments with depth reflect variations in the parent material. The lateral continuity of the layers allows proposal of a parent material stratigraphy for colluvium in these foot-slope positions in the Ridge and Valley Physiographic Province.