HOLOCENE EOLIAN ACTIVITY IN THE MINOT DUNE FIELD, NORTH-DAKOTA

Stabilized eolian sand is common over much of the Great Plains region of the United States and Canada, including a subhumid area of similar to 1500 km(2) near Minot, North Dakota. Eolian landforms consist of sa nd sheets and northwest-trending parabolic dunes. Dunes and sand sheet s in the Minot field are presently stabilized by a cover of prairie gr asses or oak woodland. Stratigraphic studies and accelerator mass spec trometry radiocarbon dating of paleosols indicate at least two periods of eolian sand movement in the late Holocene. Pedologic data suggest that all of the dune field has experienced late Holocene dune activity , though not all parts of the dune field may have been active simultan eously. Similar immobile element (Ti, Zr, La, Ce) concentrations suppo rt the interpretation that eolian sands are derived from local glaciof luvial and glaciolacustrine sediments. However, glaciolacustrine and g laciofluvial source sediments have high Ca concentrations from carbona te minerals, whereas dune sands are depleted in Ca. Because noneolian- derived soils in the area are calcareous, these data indicate that the Minot dune field may have had extended periods of activity in the Hol ocene, such that eolian abrasion removed soft carbonate minerals. The southwest-facing parts of some presently stabilized dunes were active during the 1930s drought, but were revegetated during the wetter years of the 1930s. These observations indicate that severe droughts accomp anied by high temperatures are the most likely cause of Holocene eolia n activity.