Morphology and Mineralogy of a Pre-Wisconsinan Paleosol in Iowa
1986
Thompson, Michael L.
A paleosol covered by Wisconsinan till was studied to investigate pedological development before burial and to explore the effects of glacial overriding on certain morphological features. Samples of the paleosol were collected from an exposure in a limestone quarry. Particle size distribution, pH, total K₂O content of the clay fraction, and clay mineralogical analyses were conducted on disturbed samples. Undisturbed samples were impregnated with a polyester resin and examined in thin section. The paleosol was divided into three zones that appeared to correlate with lithologic and/or pedologic discontinuities. The upper zone consisted of fine-textured accretionary material that perhaps was deposited ahead of the advancing Wisconsinan ice. A lack of clay films in the field and pore argillans in thin section coupled with evidence of minimal smectite alteration suggested that this segment of the paleosolum was weakly developed. On the other hand, plasma separations, papules, and slickensides indicated that some physical reorganization of the soil had probably occurred. The middle zone, characterized by Al-interlayered smectite in the clay fraction, illuviation argillans, and a sand content higher than the zone above, was interpreted to be an older segment of the paleosol developed in fine-textured erosional debris of Pre-Illinoian age under poorly drained conditions. The lower zone was heterogeneous with respect to both macromorphological and micromorphological features. It was interpreted to be a weakly weathered, Pre-Illinoian till.
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