Fragipan Horizons in Soils of the Memphis‐Loring‐Grenada Sequence in West Tennessee

Abstract

AbstractThe distribution of soils on the loess‐mantled landscapes of west Tennessee does not fit the traditional concept that the older, more strongly developed soils occur on the more stable positions in the landscape. The objective of this study was to attempt to ascertain whether the development and distribution of these soils were related to weathering associated with the modern landscape or whether they were in part relict from the earlier period of weathering. Power augers were used along west to east transects to determine the characteristics and thickness of the three identifiable loess sheets involved and to explore their relationship to the distribution of soils within landscapes at different points along the loess thickness sequence. The top of the Roxana loess was everywhere marked by a distinctly brittle zone 1 to 2 m thick. Evidence that the brittle zone in the top of the Roxana is a product of pre‐Peorian weathering is the fact that it occurs under calcareous loess near the bluff and can be traced eastward under the thinning Peoria loess until it grades into the fragipan horizons within the sola of the Loring and Grenada soils. The stratigraphic, geomorphic, and morphologic evidence leads to the conclusion that the fragipan horizon of the Loring and Grenada soils is a relic of pre‐Peorian weathering that has undergone subsequent modification by processes related to the modern surface.