Abstract This field guide describes four exposures of glacigenic sediment along the Missouri River bluffs east of Omaha, Nebraska. Field trip stops include Loveland, Iowa, which is the type section of the Loveland Silt and Pisgah Formation (Illinoian and Early Wisconsinan loess) and Crescent Quarry, which exposes the type Nebraskan till. Additionally we will examine core samples of the Kennard Formation, a new stratigraphic unit consisting of multiple pre-Illinoian loesses. We also present recent results on the pre-Illinoian till stratigraphy in the Missouri River valley region. A variety of evidence indicates that the present location of the Missouri River valley originated sometime between deposition of the youngest (pre-Illinoian) till and the (Illinoian) Loveland Silt. The spatial distribution of the youngest pre-Illinoian till further suggests that this reach of the Missouri River (along the Iowa-Nebraska border) was established as an ice-marginal stream along the western terminus of the last pre-Illinoian glaciation.

ABSTRACT The Driftless Area is a region of roughly 22,000 km 2 almost entirely in southwestern Wisconsin and adjacent northwestern Illinois that contains no evidence for glaciation during the Quaternary. Both in terms of topography and geomorphic process, it stands in stark contrast to the surrounding glaciated landscapes of the Midwestern United States. The nearly flat-lying Paleozoic sedimentary rocks in the region are deeply incised by the dendritic drainage system of the upper Mississippi and lower Wisconsin Rivers and numerous of their tributaries. Records of geologic processes that predate the Quaternary glaciations are exposed at the near-surface. The landscape is blanketed by loess of the Kieler Formation and was affected by mass wasting and a range of periglacial processes that were pervasive during permafrost conditions that existed between 33 and 14 ka. Post-glacial fluvial systems preserve myriad examples of channel adjustment to changes in sediment supply from the transition of glacial to interglacial conditions, changes in discharge across periods of Holocene climate change, and responses to Euro-American settlement of the landscape.

ABSTRACT Loess mantles upland summits across much of the Driftless Area of southwestern Wisconsin and its origin and paleoenvironmental significance has been a focus of research since the nineteenth century. Although the Driftless Area was ice free through the many glaciations of the Quaternary, long-term preservation of loess was limited by post-depositional erosion across much if not all of this highly dissected landscape, erosion that was likely accelerated under periglacial conditions during glaciations when ice sheets were nearby. Loess preserved today includes four members of the Kieler Formation and two older loesses known only from one locality. The Peoria Member, the youngest, thickest, and most extensive member of the Kieler Formation, was deposited during and just after the peak of the last glaciation. Its main sources include both the Mississippi River valley and the Iowan Erosion Surface and glacial outwash surfaces farther west in Iowa and Minnesota. More research is needed on the relative contribution from each of these sources to the Peoria Member, and on the sources of older loess units. Eolian sand, often forming dunes, covers extensive low-relief landscapes in the northern Driftless Area, the Mississippi and Wisconsin River valleys, and smaller areas elsewhere in the region, overlying sandstone bedrock, stream terraces, and the former bed of Glacial Lake Wisconsin. These sands are stabilized by vegetation today but were active during and just after the period of Peoria Member deposition. Thus, large areas of eolian sand acted as surfaces of transport where loess did not accumulate but rather was conveyed far downwind of its sources. Colluvium that is a mixture of bedrock-derived sediment and loess covers bedrock slopes throughout the Driftless Area. A variety of geochronologic, geomorphic, and stratigraphic evidence supports the hypothesis that this colluvial mantle formed mainly in the cold, periglacial environment of the last glaciation, with only limited modification during the Holocene. A new research effort, incorporating modern geochemical and geochronological techniques, could provide important insights on the processes that originally produced the colluvial mantle and those that are acting on it today.