SOURCE AND PALEOCLIMATIC SIGNIFICANCE OF LOESS IN SOUTHEAST SOUTH DAKOTA

The Great Plains region of North America is covered by some of the most extensive loess deposits in the world. In South Dakota, loess deposits reach their maximum thickness in the extreme southeastern corner of the state. Loess can provide valuable paleoclimate information including paleowind patterns, and may provide clues to the timing of glacial retreat. Geochemical analysis via XRF and grain size analysis were performed to determine the character and provenance of South Dakota loess, and optically stimulated luminescence (OSL) dating was performed to determine the timing of deposition. Initial study results indicate that South Dakota loess has a similar character to Peoria Loess in Nebraska. The South Dakota loess samples exhibit a relative uniformity in grain size and geochemistry, and show a similar grain size distribution and K/Rb ratios to Peoria Loess. Ti/Nb ratios are slightly higher in South Dakota loess, possibly due to a dust source from Missouri River sediment. Results from OSL dating will confirm if South Dakota loess is time equivalent to the Peoria Loess. In addition, ages of loess mantling till may provide a minimum age for the retreat of the James Lobe of the Laurentide ice sheet in southeastern South Dakota during the Late Wisconsinan glaciation.