Late Pleistocene Climate Record in the Eustis Loess Section, Nebraska, Based on Land Snail Assemblages and Magnetic Susceptibility

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Abstract
Based on multivariate analysis of mollusk assemblages and magnetic susceptibility of the Eustis section in western Nebraska, the climate of the Peoria loess steppe was relatively mild and, in terms of annual precipitation, relatively moist during the advance stages of Woodfordian ice. It was cold and dry during ice retreat. The diversity and composition of mollusk species indicates that the extreme cold and dry climate was reached during the late phase of Peoria time, in mollusk zone MZ3. Although soil moisture during the growing season at that time was high, the growing season was short and annual precipitation totals were low. Low values of magnetic susceptibility imply relatively rapid dust deposition during this interval, Judging from the current ecological tolerance of the species, no closed forest existed in the area. Only scattered shrubs or isolated tree stands may have been present. The late Peoria MZ3 assemblage compares favorably with theColumellafauna of Europe. In contrast, the early Peoria mollusk assemblages MZ1 and MZ2 compare well with the European pleniglacialPupillaassociations. Based on available14C dates from the studied region and on assumed relation of magnetic susceptibility to sedimentation rates, the estimated age of the MZ1 and MZ2 zones is 24,000 to 16,000 yr, whereas that of MZ3 is 16,000 to 12,000 yr.