MICROMORPHOLOGY OF SELECTED MASSACHUSETTS FRAGIPAN SOILS

The micromorphology of five till-derived soils presently classified as Dystrochrepts was studied to evaluate the degree of their pedogenic development in order to establish the presence of fragipans. Thin-section observations indicated that Btx horizons contain common void argillans and clay bridges. This contrasts with the Cd horizons, which contain few and mostly poorly developed argillans. Skeleton grains in the bleached Btx horizon prism faces are relatively clean and occur in a silty matrix. Ferrans and ferriargillans occur along the prism boundaries within the fragipan matrix. Mangans and ferrans are the most typical features in the Cd horizons, coating the surfaces of the plates that are characteristic of these horizons. The fabric of Btx horizons is predominantly skelsepic, while that of Cd horizons is dominantly insepic to asepic. BCd horizons are similar to Btx horizons but with less well developed argillans and lacking bleached prism faces. The transition from the well-developed Btx horizon fabric to the poorly developed agrillans and plasma separations of the underlying parent materials (Cd horizons) indicates pedogenic development within the fragipans.