Surficial Sediments on Undulating Cary Ground Moraine in Central Iowa

摘要

A post-glacial surficial sediment 0.3 to 3.6 m or more thick overlies the Cary till in central Iowa, and is usually separated from the till by a discontinuous, often weakly-expressed stone line. In the areas studied, the surficial sediments cover more than 90 per cent of the present landscape and form a major soil parent material. Although deposition of the surficials has caused a reduction in topographic relief on the Cary ground moraine, thickness of the surficials is not predictable from the present topography due to burial of channels and alluvial drowning of highs. The surficials were found to be mineralogically similar to the underlying till, but more homogeneous, indicative of mixing. X-ray data suggest that clay minerals in the surficials are slightly more weathered than those in the underlying till. Carbonate contents are variable due to leaching, secondary enrichment and the local abundance of aquatic and pulmonate fossils. The surficial sediment gradually becomes finer textured from the crest of a swell to the bottom of a swale. (Author)