Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/1996
Publication Date: N/A
Interpretive Summary: In order to understand the development of fragipan horizons in loess (fine textured, windblown) soils, the contribution of the different loess layers must be understood. Past research has suggested that fragipan layers represent pre-existing erosional surfaces in one specific loess layer that were subsequently buried, and their formation is not related to landscape features. Our findings show conclusively that fragipan horizons can incorporate the boundary between different loess layers, indicating their formation is controlled by landscape rather than depositional features. Thus, a soil formation approach can be used to explain their occurrence and assist natural resource personnel (NRCS, extension service) in the design of management systems specific for soils with fragipan horizons
Technical Abstract: The upland areas adjacent to the modern day Mississippi River floodplain are mantled by up to several meters of loess overlying coastal plain or alluvial sediments. Several loess deposits have been identified in the southern or lower Mississippi River Valley (LMRV) and are thought to have a direct relation to fragipan occurrence and development. Previous investigations in western Tennessee have led to the conclusion that fragipans in the region are the result of pre-Peoria weathering of the Roxana Silt. The current study investigates the stratigraphic relationships between loess units and fragipans throughout the LMRV. Five sites located in the loess uplands from northwestern Tennessee to southeastern Louisiana were studied. At each site, a Memphis (Typic Hapludalf)- Loring (Typic Fragiudalf)-Grenada (Glossic Fragiudalf) catena was sampled. In the field preliminary stratigraphic breaks were identified by changes in texture, particularly an increase in sand or clay content, and by color changes. Soil samples from each horizon of each pedon, plus augered samples from up to 6 m depth, were analyzed in the laboratory for clay-free particle size distribution and mass magnetic susceptibility. In addition, the coarse silts (50-20 um) from all Memphis pedon horizons were separated and analyzed for total Fe, K, Mg, Ca, Ti, and Zr. The data were analyzed by k-means cluster analysis to identify stratigraphic breaks in the loess and underlying coastal plain or alluvial material deposits.