LATE QUATERNARY EOLIAN SAND STRINGERS OF NORTHEAST IOWA

The Iowan Surface of Northeast Iowa is a low relief, extensively eroded, Pre-Illinoian till plain. It is thought to have formed by severe erosion in a periglacial environment during late Quaternary time. Much of the surface is blanketed with loamy sediments of eolian origin. In places, sandy deposits derived from Pre-Illinoian till are also present. These eolian deposits are commonly separated from the underlying till by a stone line with abundant ventifacts present. Extensive deposits of eolian sand occur on the east and southeast side of the Cedar River in Black Hawk and Bremer Counties. County soil surveys refer to these features as dune like, although we choose to call them sand stringers to emphasize their linear orientation and low profiles. A GIS study using soil surveys produced several maps showing the distribution of the stringers, which display a strong northwest-southeast orientation (~310 degrees). They typically rise 3-5 m above the surrounding Iowan Surface, have widths from 20-100 m, and can be traced for up to 20 km. The stringers are continuous across the landscape and in places, they have even blocked small drainageways and caused ponding and the formation of very poorly drained organic soils. Particle size analyses, study of sand surface textures, and other investigations are currently underway in an effort to better understand the characteristics of these sediments. The stringers appear to be very similar to features described from the Iowan Surface of southeastern Minnesota, where formation in a late Quaternary periglacial environment has been suggested. The sand stringers of southeastern Minnesota have yielded thermoluminescence dates of ~15,000-11,000 years before present. Our stringers presumably were deposited during this same time span or perhaps somewhat earlier. The focus of this project is to describe and map the distribution of these geomorphic features using GIS software and to develop a broader paleoclimatological context for the upper Midwest during late Quaternary time.