Decatur County, pre-Illinoian till, clast pavements, Pleistocene stratigraphy
The Pleistocene stratigraphy and sedimentology of two quarry exposures near Grand River and Decatur City in Decatur County, Iowa document a sequence of Pleistocene sediments overlying striated Pennsylvanian limestone which represent at least two pre-Illinoian glacial advances into the ancestral Grand River valley. Two pre-Illinoian diarnictons separated by a clast pavement were observed at the Decatur City quarry; a single diarnicton was present at the Grand River quarry. At both quarries, the diarnictons exhibit comparable lithologic properties and are genetically interpreted as basal tills. The pre-Illinoian tills are tentatively correlated with the Alburnett Formation in eastern Iowa, primarily on the basis of clay mineralogy data. Fluvial erosional and depositional processes succeeded till deposition at both quarry sites. The tills are overlain by a fining-upward fluvial sequence upon which a well developed Yarmouth-Sangamon paleosol is developed. Sangamon Soil developed upon a pebbly diarnicton overlies the fluvial sediments. The pebbly diarnicton probably originated as colluvium from pre-Illinoian tills at higher landscape positions during late Sangamonian pedimentation. Lastly, periglacial conditions during mid-to-late Wisconsinan time resulted in multiple episodes of loess deposition corresponding to, in ascending order, the Pisgah Formation, Farmdale Soil and Peoria Loess, all Wisconsinan stratigraphic units.
Journal of the Iowa Academy of Science
© Copyright 1993 by the Iowa Academy of Science, Inc.
Schilling, Keith E. and Stewart, Robert A.
"The Pleistocene Glacial Record at Two Quarries in Decatur County, Iowa,"
Journal of the Iowa Academy of Science: JIAS, 100(3-4), 65-71.
Available at: https://scholarworks.uni.edu/jias/vol100/iss3/3