STRATIGRAPHIC, HYDROLOGY AND GEOPHYSICAL INVESTIGATION ON A POSSIBLE FEN UNIT LOCATED ON THE NACHUSA GRASSLANDS, FRANKLIN GROVE, ILLINOIS

The Nachusa Grasslands is approximately 4000 acres of undisturbed and seeded tall grass prairie and contains numerous spring-fed wetlands, one of which is a hypothesized fen. The peat area is 0.6m in thickness near the center with sandstone at the base and near the edges. The purpose of this research is to determine if this area of Nachusa Grasslands is a fen with a deep source water supply. The conduited sandstone springs runoff fluctuates very little and is not dependent on precipitation. The first four months of 2012 had higher than normal precipitation in the form of snow and rain and the last 8 months were classified as a moderate drought. The outlet flume water level fluctuated less than 2 cm while the average level upstream of weir dams remained between 15 cm and 17 cm. Using well log completion reports available from USGS for private wells within 5000 m of the spring and geo-spatial analysis of local outcrops a conceptual stratigraphic model was produced. Conductivity measurements and seismic surveys show an offset in the subsurface structure beneath the fen channeling water to the fen from depths in excess of 21 m. This is believed to be a lateral extension of other structural features already identified in the area: the Sandwich Fault Zone, Ashton Arch and LaSalle Anticline.