Geomorphic Relationships in the Fragi Taxon across Pennsylvania: Clues to Genesis and Cementation Mechanisms

NRCS Soil Survey data indicates that there are 33,081 km2 of soils with fragipans occurring in every county of Pennsylvania (28% of the state's area). The horizon is known to limit development and production potential for land uses dependent on good drainage and deep rooting. Previous research in Pennsylvania has found that fragipans form primarily in transported parent materials, are more dense and thicker in areas of poor drainage, and are present deeper in the soil profile in areas of steep slopes. However, the criteria used to identify the horizon are based on subjective-non-laboratory based measures that make absolute recognition impossible and the likelihood of the taxon representing gradations of occurrence more likely. The completion in 2007 of Pennsylvania's SSURGO mapping provides the opportunity to examine models of fragipan development with high resolution digital mapping data. We selected soil mapping units with a dominant fragi taxon (soil associations, mine land, urban land areas removed from analysis) to examine taxon distribution within physiographic provinces. Within provinces, NRCS Official Series Description data and surficial geology (Pennsylvania Geologic Survey data) was also used to discern relationships in fragipan density between parent material and elevation, aspect, slope and geomorphology (potential peri-glacial influence of loess contributions) with fragi taxon distribution. We also examine differences in taxons by physiographic province at the sub-order, great group and sub-group levels.