Mineralogical Analysis of Aeolian Dune Deposits, White River Badlands, South Dakota

The goal of this study is to test our hypothesis that sand dunes in the White River Badlands (WRB), South Dakota, northern Great Plains, formed during one or more prolonged prehistoric droughts. WRB dune fields are located on tabletops north of the White River in southwestern South Dakota. These parabolic dunes have maximum relief of 30 m and open to the northwest, consistent with the dominant wind direction for the region. Currently, dunes are stabilized by a drought-adapted, mixed grass prairie community.

Sand dunes form when 1) prolonged drought kills prairie vegetation, allowing wind to erode and transport sediment, forming sand dunes in drought conditions, or 2) local stream sediment supplies increase, causing dune formation under nondrought conditions. Thus, if mineralogical compositions of dune sands are equivalent to compositions of nearby stream sands, then dunes formed because of increased sand supplies, as opposed to drought.

To test the hypothesis that WRB dunes formed in drought, the investigators made quantitative and qualitative comparisons of dune and stream sand compositions. Summers of 2015 and 2016, investigators collected representative samples from WRB dunes and the White River channel. Investigators analyzed sand compositions using two methodologies. First, using a petrographic microscope, investigators identified 300 grains in thin section from each sample to produce a statistically valid modal composition based on quartz, feldspar, and rock fragment content. Second, using the petrographic microscope, investigators identified distinct mineralogical associations in each sample for comparison. The presentation will include results of these quantitative and qualitative analyses.