Time as a Factor in the Genesis of Four Soils Developed in Recent Alluvium in Pennsylvania

Abstract

AbstractFour soils developed in recent alluvium in the Ridge and Valley physiographic region of central Pennsylvania were studied in an attempt to relate chronologic age to pedologic age. Wood or charcoal found at the boundary between a recent and a buried soil profile at each site was radiocarbon dated. These dates were as follows: (i) < 205, (ii) 320 ± 80, (iii) 470 ± 80 and (iv) 1955 ± 80 years B. P., and indicate the maximum age of the alluvium in which the recent soil profiles developed. The relative distinctness of horizons evaluated by a field morphology rating scale, the volume (in cross section) of oriented illuvial clay films and the in situ weathering of clay minerals in these soil profiles indicate that morphological properties are effective in distinguishing chronologic age differences in alluvial soils which differ by approximately 1,500 years in age, but are not effective when the age differences are only a few hundred years. The data also indicate that cambic horizons can develop in <200 years and are still present after 2,000 years of soil formation.