NEW DATA FROM LOESSES AND PALEOSOLS OF THE US MIDWEST

Loess/paleosol series of the US Midwest provide long-term proxy records of Quaternary sedimentation, climate and environments south of the glacial limits of North America. Three key sections were investigated at Wittsburg Quarry (Arkansas), Missouri Valley (Iowa) and Eustis Ash Pit (Nebraska) by geochemical, paleomagnetic and micromorphological analyses. Below the surface soil at each section, four loesses are present. They are separated by three well-developed paleosols.

The Crowley's Ridge loess is the oldest loess unit at the sections under study. At Wittsburg, it lies on Pliocene gravel, at Eustis it immediately overlies the Lava Creek B ash layer, and at Missouri Valley it lies directly on the Pre-Illinoian till surface. A well-developed paleosol modifies this loess at all three sections. This paleosol has not previously been reported in western Iowa or eastern Arkansas. At all three sites, it is immediately overlain by the Sangamon paleosol solum which itself represents pedologically-altered Loveland loess. This means that the Loveland loess is much thinner than previously suggested. The Sangamon paleosol is well developed and readily correlated between Wittsburg and Missouri Valley, but is probably partly eroded at Eustis. It has luvisolic properties but with much more clayey pedogenic texture than modern luvisols, and has no clear eluvial horizon. The overlying Roxana loess at Wittsburg and its equivalents at Eustis and Missouri Valley are mostly altered by soil formation. At Wittsburg and Missouri Valley, this soil is called the Farmdale paleosol. On the basis of its pedogenic features it correlates to the Gilman Canyon Formation paleosol at Eustis. This soil has chernozemic properties at all three sections, but at Wittsburg it is less developed. At all three sections, this soil has ancient krotovinas, hence the gley features observed must be interpreted as post-burial changes. In the upper part of all the sections, the thickest Peoria loess is developed and shows the properties most typical of loess. From the Peoria loess to the Loveland loess, the correlations proposed are well corroborated by numerous published TL and 14C dates. Below the Loveland loess, only a few TL dates are available. Mass-specific magnetic susceptibility and its frequency-dependence correlate well with lithology and have maxima at the top of each paleosol.