Silty mantles and fragipans in Pennsylvania soils

Open Access
Author:
Lindeburg, Katherine S.
Graduate Program:
Soil Science
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Patrick Joseph Drohan, Thesis Advisor
Keywords:
  • SEM
  • grain microfeature
  • particle size distribution
  • windblown sediment
  • eolian
  • surface texture
Abstract:
The physical, mineralogical, elemental, and micromorphological properties of loess and non-loessial soil pedons were evaluated in order to evaluate the potential presence of eolian materials in the non-loessial pedons, formed predominately from pre- and late Wisconsinan aged glacial till, colluvium, and/or residuum. In addition, potential timing of eolian deposition was investigated based on the hypothesized timing of fragipan prism morphology formation. A combination of physical, chemical, mineralogical, and descriptive imaging techniques were used.<P>Characteristics of eolian contributions to Pennsylvania soils were based on data from known loess pedons. Loess pedons were found to exhibit a uniform, silt-rich particle size distribution with depth, the presence of an abrupt lower boundary with underlying sediment of different parent material age or type, and grains with microfeatures diagnostic of multiple transport processes. Additionally, the surface properties of quartz coarse silt and very fine sand grains in loess pedons indicate only minor grain alteration from an eolian environment. The more common and better expressed surface features diagnostic of fluvial and glacial environments indicate a complex transport history of the sediment prior to eolian deposition. The small number of diagnostic eolian features and abundance of fluvial and glacial features observed on particle surfaces of the loess pedons may reflect a brief duration and/or short distance of wind transportation prior to deposition. The colluvial and/or residual hillslope pedons and the pre-Wisconsinan glacial till pedon exhibit the general trends and properties observed in the loess pedons. Silty mantles in the non-loessial pedons were attributed to an eolian origin based on the following observations and pedon properties: presence of a lithological discontinuity; abrupt differences in morphology, various physical properties, and grain micromorphology in the silt-rich surface and shallow subsurface horizons compared to the deeper less silty horizons; and a moderate degree of grain surface imprints of diagnostic glacial and eolian environments in silty surface and shallow subsurface soil horizons.<P>Eolian materials were observed in some but not all fragipan horizons of the non-loessial pedons. Results suggest the timing of vertical cracking and initial development of the prism structure occurred during the early part of the late-Wisconsinan. In the pre-Wisconsinan glacial till soil, results suggest that the deposition of external, eolian materials followed the last glacial period. This suggests that eolian deposition occurred sometime after the formation of prismatic structural units in the fragipan horizons.