Postglacial environments in relation to landscape and soils on the Cary drift, Iowa

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Vol: 35, Issue: 549

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Patrick H. Walker
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The objectives of this study were to evaluate environmental and time factors in the genesis of soils and soil landscapes on the Cary drift in Iowa, with special reference to soils of the Clarion toposequence.The stratigraphy of five bogs along the Des Moines lobe was studied in detail; and as a result, a general bog stratigraphy was established for the Cary drift in Iowa. The stratigraphic zones and appropriate radiocarbon dates are as follows: upper muck zone (UM), 0-3,000 years; upper silt zone (US), 3,000- 8,000 years; lower muck zone (LM), 8,000-10,500 years; lower silt zone (LS) , 10,500-13,000 years; Cary sediments, >13,000 years. Pollen and macro-fossil data indicated that forest vegetation was prominent on the landscape until 8,000 years ago; and subsequently, herbaceous prairie flora dominated the landscape up to the time of settlement. Erosional rates for hillslopes and depositional rates for bog areas were calculated for each of the stratigraphic zones given. The muck zones represent relatively slow hillslope erosion and a preferential accumulation of organic matter in the bog; the silt zones represent relatively rapid erosion and a preferential mineral sedimentation in the bog. Hillslope erosion 8,000 to 3,000 years ago was the greatest of all the intervals and removed an average of 1.7 feet of soil from the upper slopes of the Colo bog watershed and 5.3 feet from the upper slopes of the Jewell Watershed. The extent of erosion and deposition during this interval insures that most soils of the Colo and Jewell watersheds developed on relatively young surfaces under prairie vegetation. Many soils of the Webster, Harpster and Glencoe series developed the upper part of their solum in surficial sediment rather than the drift, and their profile properties relate to the last 3,000 years of prairie environment.