REDOXIMORPHIC FEATURES IN SOILS OF THE TRIASSIC CULPEPER BASIN1

Abstract

Conflicting observations have been reported about redoximorphic features in soils derived from red Triassic sediments. Previous laboratory research has shown that development of redoximorphic features is sometimes inhibited in these sediments. Soil morphological descriptions made under the auspices of The National Cooperative Soil Survey, however, include redoximorphic features consistent with their drainage status. The objective of this study was to examine the relationship between soil characteristics and development of redoximorphic features in these soils. Eleven pedons located along two topohydrosequences in the Triassic Culpeper Basin of Maryland were described and characterized. In addition, water table depths were measured biweekly over a 2-year period at each pedon during the wet season. Similarly drained, yet morphologically different pedons were observed occupying the lower backslope, footslope, and toeslope positions of both topohydrosequences. Differences in organic carbon content and soil temperature did not explain the observed morphological differences among these similarly drained soils. The nature of the parent material, however, appears to control the development of redoximorphic features in the soils of the Triassic Culpeper Basin of Maryland. Lithological discontinuities were observed at the boundary between horizons with yellow and red hues (i.e., 5YR) in soils that occupy the footslope and toeslope positions. These discontinuities are believed to represent the incorporation of alluvial debris in these soils. Within pedons whose upper sola were influenced by alluvial additions and a persistent seasonally high water table, substantial development of redoximorphic features was observed. Within hydrologically-similar pedons derived mainly from Triassic residuum, redoximorphic features were weakly expressed. Hydromorphological features are formed by redox processes, but the particular expression may be affected by the nature of the parent materials. These results may be useful to field soil scientists for their assessment of the correct drainage class of these soils.