EXPLORING ISSUES OF VARIABLE OSL AGES IN THE STUDY OF QUATERNARY DUNE HISTORY IN UPPER MICHIGAN, USA

OSL has been used to identify periods of Holocene dune activity in Upper Michigan over the past decade. All studies have employed SAR protocol but reported ages of dune activity differ by as much as several thousand years. Earliest efforts employed only a few sample sites/ages (5/10) and returned ages ranging from 7 to 5.5 ka; more recent work employing ~40 sites and over 100 ages suggests ages of 10.5-8.0 ka. The areal extent and geomorphic settings of studies are similar; several areas are covered in both earlier and later studies.

We explored possible reasons for the age disparity between the two sample sets by returning to Upper Michigan and resampling five dune sites. We collected side-by-side samples at multiple depths within the deposits. Of the 24 samples collected, a duplicate set of 12 was sent to each of two independent labs where samples were assessed using state of the art SAR protocol. In addition to retesting the age of the dunes, a secondary goal of this study is to assess the impact of interlab variability on ages from samples collected from the same sites and depths.