A FORMAL LITHOSTRATIGRAPHY FOR THE QUATERNARY OF MINNESOTA

The Minnesota Geological Survey has created a formal lithostratigraphy for the Quaternary deposits of Minnesota that will be published on-line and in-print, fall 2011. We followed guidelines of the North American Commission on Stratigraphic Nomenclature (2005) to create a framework for establishing formal lithostratigraphic units in Minnesota, and we evaluated the approximately 120 lithostratigraphic names and units that have been identified and used in Minnesota since the time when geologic mapping of glacial deposits began. Of these, eighty-one (81) units are considered to be useful lithostratigraphic units of formation and member rank, and these are formally accepted in this open-file report or will be in future volumes. These 81 units include previously named formal lithostratigraphic units that are recognized and accepted as originally defined, but also formally defined units that we have revised or redefined to better fit into our stratigraphic framework. The remaining lithostratigraphic units have been used informally in earlier reports or are newly named. Twenty-three units are no longer considered valid as lithostratigraphic units are abandoned even though some of these are well-known among state geologists. These units include previously used units of both formal and informal status. Many units, especially in the subsurface, are undefined at the present time because their character and extent are poorly known.