INTRODUCING THE FERTILE DUNE FIELD, MINNESOTA, USA: DUNE TYPES, WIND DIRECTIONS AND SAND CHARACTERISTICS AT AGASSIZ ENVIRONMENTAL LEARNING CENTER

The Fertile Dune Field is located on the Eastern shores of Glacial Lake Agassiz near the town of Fertile, Minnesota. The dune field formed after the Sand Hill Delta, which it overlies, was exposed to eolian mobilization following a significant retreat of Glacial Lake Agassiz from the Herman shoreline. The goal of this project was to begin study of the eolian history of the dune field within the boundaries of the Agassiz Environmental Learning Center. This presentation deals with the dune types and sizes, the wind directions(s) represented in the dune field, grain size distribution of selected sample sites and sand grain surface morphology. The project utilized GIS for spatial analysis, field work including sample collection for lab analysis and SEM grain imaging. Our results indicate that the dune forms in this location could be grouped into small, medium, and large barchan and parabolic forms based on size and slopes. The large barchans had a strong north to south orientation while the small parabolic dunes were dominantly south to north orientation. Sampling pits were excavated in three dunes, with one on the nose and arm at each location. Paleosols were found in three of the five excavations indicating a minimum of two eolian activation episodes. There was a detectable change in grain size distribution between layers separated by a paleosol. In one location no paleosol was found but there was a less distinct change in grain size distribution between subsurface horizons. Predominant grain size was upper fine sand in higher layers and lower medium sand in lower layers. SEM imaging showed that the sand grains exhibited varying degrees of sphericity, roundness, sorting, and eolian weathering textures among samples. Many grains exhibited highly rounded forms with entirely frosted textures, while others were angular with limited frosting. These observations are consistent with short distance eolian transport.