Monday, November 5, 2007
115-4
Mineralogy and Stratigraphy of Polygenetic Soils on Different Geomorphic Surfaces of the Bluestem Hills of East-Central Kansas.
Upland soils in east central Kansas have a complex genesis, are polygenetic and often contain one or more paleosols. These soils form in multiple parent materials including loess, colluvium, and residuum. Quaternary loess/paleosol investigations have largely ignored this region of Kansas, as the total loess thickness on uplands is <2 m thick. In this study, the objectives are to examine the stratigraphy and mineralogy of the soils of interest and how these characteristics vary within soil profiles and across landscapes. Three pedons were sampled and described on different geomorphic positions in the Lower Cottonwood River watershed in Chase County, Kansas. This study area is within the Bluestem Hills Major Land Resource Area of east-central Kansas. The mineralogy of the total silt and clay fractions were semi-quantitatively determined for selected horizons with X-ray diffraction spectrometry. Accelerator mass spectrometry (AMS) was used for numerical dating and determination of stable carbon isotope values for selected paleosols. Mineralogy varied within profiles and between landscape positions. The two upland pedons were similar as the horizons sampled in the modern soil contained approximately 50% smectite, and the paleosol horizons contained approximately 25% smectite and were generally more mixed. In contrast, the pedon sampled on the terrace position was dominated by smectite throughout the profile. Radiocarbon ages ranged from 24,500 to 19,000 yr BP and δ13C values were between -19 and -17 ‰ (PDB), indicating that the paleosols were formed in Gilman Canyon aged loess or Severance Formation colluvium or alluvium, under a mix of C3 and C4 vegetation. In conclusion, differences in mineralogy may have been inherent to the parent materials, or they may have resulted from the different soil forming factors acting upon the modern soil and the paleosol during pedogenesis. Results from this study will contribute to Quaternary loess/paleosol knowledge in east-central Kansas.
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