The New and Ancient Landscape: A story of soil-landscape evolution in the karstic regions of southwest Wisconsin
Wednesday, November 2, 2005
4:00 - 5:00 pm
LFG 102, UNLV Campus
Dr. Cynthia Stiles
Assistant Professor - Pedology
Departments of Soil Science and Geology/Geophysics and the Nelson Institute for Environmental Studies
University of Wisconsin, Madison
http://www.soils.wisc.edu/soils/people/faculty/stiles.htm
Abstract
One of the most interesting topics in weathering systems is deciphering systematic evolution of soils forming in karst. Humid region weathering of carbonate bed rock is sensitive to environmental impacts, such as changing climate regimes and human perturbations. Karst locations with large influxes of glacial material provide a chance to evaluate the influence of external materials on weathering intensity and to establish a conceptual model of soil processes involved in thick soil accumulations.
Physical and micromorphological assessment of soils forming on dolomite-rich bedrock in the southern Driftless Area (sDA) of Wisconsin reveals a pattern of complex pedogenesis dominated by surficial additions/transformations and dolostone epikarst degradation. Observations of landscape trends reveal an attenuated rill and valley morphology dictated by ancient regional deformation and localized hydrogeologic patterns, in both the vadose and groundwater zones. Examinations of soil profiles in watershed transects show morphologies with strong differentiation between the upper portion of these soils (quartz-rich silt loams) and underlying redder hued clay-rich subsoils (also called the Rountree Formation) abruptly contacting bedrock. The high clay contents of these subsoils (41-83 wt%) suggests that the relatively high purity dolomite cannot be the sole parent material for sDA soils, but rather serve as a foundation that provides karst sediment accumulation zones and high base saturation through gradual dissolution. Thin sections supports this concept by showing pervasive intergranular clay intercalation between dolomite grains of the saprolite, suggesting replacement of calcite cements from the original bedrock by pedogenic clays (sandy loam horizons with clay component dominated by fine to very fine clays) derived from the overlying silty materials. Geochemical analyses of soil compositions indicate long-term multi-generational pedogenic clay accumulations were the main mechanism of formation. The stratigraphy, spatial discontinuity and time-transgressive nature of the Rountree Formation suggest it is a product of long-term pedogenic inputs into the epikarst interface and subsequent dissolution of the carbonate foundation over long episodes of weathering.
Updated September 14, 2005