Upcoming talk: Sept 9, 3:05, UofA Geosciences Colloquium, Gearhart Hall 26.

Association for Women Geoscientists Distinguished Lecture:

Older than Dirt? Or Older than the Hills? New findings on the Quaternary History of the Buffalo National River

Amanda Keen-Zebert, DRI

Abstract: Although the Buffalo River was the first US designated National River, has the highest topography between the Appalachians and the Front Range of the Rockies, and is one of the few remaining undammed rivers, its Quaternary and geomorphic history is largely unknown. To help better define the rate of landscape evolution in the Buffalo River watershed, cosmogenic nuclide, U-series disequilibrium, paleomagnetism, and OSL measurements are being used to find the ages of cave sediments, speleothems, and stream terraces and to define surface erosion rates. Cosmogenic nuclide burial ages for coarse clastic material in higher passages in Fitton Cave suggest multiple phases of sediment aggradation beginning at ~2.2 My. Quartz OSL signals from the same sediments are saturated and thus broadly support these ages.  Maximum U-series ages for flowstones overlying the clastic sediments provide minimum ages for the underlying deposits ranging from 400–700 ka and are consistent with cosmogenic dating results. Paleomagnetism results from fine sediment overlying the oldest basal gravel and cobbles dated by cosmogenic nuclides show normal polarity and suggest deposition during the Brunhes chron (<0.78 My) or Olduvai subchron (1.77-1.95 My). Stream terrace depositional ages vary with elevation above the main channel and range from 5-15 ka for the lowest terraces to > 100 ka for higher units. Surface erosion rates average ~13 m/My but range from ~4-27 m/My and vary with lithology. The timing of sediment aggradation in Fitton Cave corresponds to climate changes associated with major advances of the Laurentide ice sheet several hundred km to the north.  Results presented here are in broad agreement with findings from other systems that are part of the larger Mississippi River drainage basin.