Poinsett Silty Clay Loam: Its Genetic Factors

The Poinsett soils of eastern South Dakota present a problem in soil classification and mapping because of local profile textural variations. Although these soils have a silty matrix which in some profiles appears to be loess, profiles only a few feet away contain admixtures of gravel, cobble, and stone. Moreover, their substrate are mottled and often stratified by color and texture. The silty materials from which the Poinsett soils are developed are more friable and appear to be more permeable than glacial till, but the admixtures of gravel, cobble, and stone make them less desirable than loess as a soil forming material. The purpose of this study is to investigate the mode of origin of the parent materials of the Poinsett soils and to compare the Poinsett soils with the Moody soils which are developed from loess, and the Vienna soils which are developed from glacial till. A comparison of field observations and laboratory analyses of profiles of Moody, Vienna, and Poinsett soils show that the parent materials of the Poinsett appear to be neither loess nor glacial till. The stratified substrata, admixture of gravel and stone, and included bodies of till indicate that the Poinsett parent materials were deposited primarily by melt waters of stagnated glacial ice. This is borne out by the abrupt textural changes in the Poinsett substrata which is characteristic of materials that have been sorted and deposited by water