LUMINESCENCE AGES FOR DUNE ACTIVATION ON A PLEISTOCENE TERRACE OF THE KANSAS RIVER VALLEY

Historically, four Quaternary terraces have been recognized within the Kansas River valley from Junction City downstream to Kansas City, Kansas. The terraces, from oldest to youngest, are named the Menoken, Buck Creek, Newman, and Holliday. The Holliday formed within the last 1000 years, and the Newman between about 14 to 4 ka, however no numerical age data exist for the Buck Creek or Menoken terraces due to their limited preservation and poorly documented stratigraphy. The Buck Creek terrace fill may be as young as 15 ka (based on morphology) and the Menoken as old as 640 ka as its fill reportedly contains Lava Creek B ash. In an attempt to constrain terrace chronology, we derived optically stimulated luminescence (OSL) ages on eolian dunes formed on a remnant Menoken tread within the Kansas River valley. Eolian dunes were dated because of their stratigraphic position directly above the previously mapped and presumed Menoken terrace. OSL dates the last period of the eolian dune activation between 35.2 and 31.0 ka, which places dune activation within the latter part of MIS 3. These dune ages chronologically overlap with the Bond Cycle between Heinrich events 4 and 3, a peak in summer insolation, and deposition of the Gilman Canyon Formation (a regional loess deposit). Interdune sediment dated to ~6 ka and may suggest a geomorphic response to Holocene drought. Dune activation between 35.2 and 31.0 ka may have been caused by drought but could have occurred in conjunction with the Buck Creek terrace formation.