Genesis and morphology of soils in and around large depressions in Clay County, Nebraska

The soil survey of Clay County, Nebraska identified soils within and on uplands surrounding some large depressions with the same soil map unit. In theory, soils found on such contrasting landscapes should be different. Three hypotheses pertaining to the genesis and morphology of these soils and their parent materials were tested. Soil and stratigraphic investigations were carried out along transects across breached (naturally drained) depressions within two sample areas in Clay County, Nebraska. Soil data indicated that within each sample area the depression floor soils had genesis and morphology similar to upland soils. However, soil data indicated the depression floor and upland soils from one sample area did not have the same genesis and morphology as the depression floor and upland soils from the other sample area. This difference was attributed to the difference in distance each of the sample areas was from the source of the loess parent material. Stratigraphic data indicated that eight to twenty-eight feet of loess, covered old landscapes that were marked by buried paleosols dating from 19,890 to 26,670 years before present. The soil parent materials above the paleosols were identified as Peoria and Bignell loesses. Data suggested that these parent materials had not been subjected to the depression forming processes because the depressions predated the Peoria and Bignell loess deposition. Particle size and mineralogic data indicated the possibility of a lithologic discontinuity at a depth of approximately 60 cm in all of the pedons studied. This discontinuity suggested the presence of the contact between Bignell and Peoria loesses within the upper part of the pedons. The results of this research indicated that the collection of detailed laboratory and stratigraphic data should be combined with the field observation of soils within a soil survey program