CRYPTOTEPHRA DATING OF A PALEOENVIRONMENTAL RECORD FROM APPLEMAN LAKE, INDIANA, USA

The melting and retreating of the continental ice sheet at the end of the Wisconsin Glacial period influenced the geomorphology and paleoenvironment of much of the Great Lakes Region and northern Indiana, including Appleman Lake, a small kettle-pond in Lagrange County, Indiana. A 2009 paleoecological study of sediment cores retrieved from Appleman Lake in 2005 established an age model of several meters of lake sediments (Gill, 2009). By using tephrochronology, a more precise age model may be established for lake sediments, and correlations can be made between sites allowing precise paleoenvironmental and paleoecological comparisons to be made over a greater region. To assess Appleman Lake sediments for the presence of trace accumulations of volcanic ash (cryptotephra), the sediment cores used in the 2009 study were sub-sampled in 5 cm depth intervals. These samples were then subjected to several phases of separation, both by particle size and density, to concentrate the tephra glass for geochemical analysis. The geochemical signatures of the tephra glass characterized by electron microprobe analyses allow for tephra found within the core to be traced to specific volcanic eruptions, establishing precise dates to the core intervals in which they are found.