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 d evelopment in order to establish the presence of fragipans. Thin-secti on observations indicated that Btx horizons contain common void argill ans and clay bridges. This contrasts with the Cd horizons, which conta in few and mostly poorly developed argillans. Skeleton grains in the b leached Btx horizon prism faces are relatively clean and occur in a si lty matrix. Ferrans and ferriargillans occur along the prism boundarie s 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 pr edominantly skelsepic, while that of Cd horizons is dominantly insepic to asepic. BCd horizons are similar to Btx horizons but with less wel l developed argillans and lacking bleached prism faces. The transition from the well-developed Btx horizon fabric to the poorly developed ag rillans and plasma separations of the underlying parent materials (Cd horizons) indicates pedogenic development within the fragipans.