PAST WIND DIRECTION IN ROCK COUNTY, MINNESOTA, AS INDICATED BY EROSIONAL FEATURES IN THE SIOUX QUARTZITE

Rock County, south western Minnesota, has been unglaciated since 550-640ka. Outcrops of Sioux Quartzite in Rock County contain evidence of aeolian erosion in the form of pits, grooves, and faceted and polished surfaces. The goal of this study was to determine past wind direction using the orientation of these erosional features. Additionally, the effect of the attitude of the bedrock on the orientation of these features was also determined.

Outcrops of the Sioux Quartzite were located with aerial photographs and a surficial geologic map. Aeolian erosional features were located and identified and orientations were measured. Pits were about 0.5cm wide and 1.0cm long and grooves were larger, around 1.0cm wide and up to 4.0cm long. Pit orientations are roughly parallel and assumed to be parallel to past wind direction. Measurements indicate that the dominant wind direction has been between N48W and N57W at some time since the area was glaciated.

In this region bedding dips shallowly toward the center of a basin. Data suggest that the orientation of the pits are not affected by the attitude of the bedding.

Future work includes: investigating the potential relationship between orientations of pits and joints; determining the effects of lichen on polished surfaces; dating eroded surfaces with cosmogenic isotopes to better constrain timing of wind erosion; and correlating these results with other paleo-wind data to gain a better understanding of regional atmospheric dynamics. Research for this study was funded by a grant from the National Science Foundation - Research Experiences for Undergraduates (REU) Program (NSF-EAR 9820249).