2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 4
Presentation Time: 1:30 PM-5:30 PM


HOFFOWER, Heidi L., Department of Geosciences, Univ of Nebraska - Lincoln, 214 Bessey Hall, Lincoln, NE 68588-0340, GOBLE, Ronald J., Department of Geosciences, Univ of Nebraska-Lincoln, 214 Bessey Hall, Lincoln, NE 68588-0340 and BLUM, Michael D., Univ Nebraska - Lincoln, 214 Bessey Hall, Lincoln, NE 68588-0340, hoffowerhl@yahoo.com

While Optically Stimulated Luminescence Dating (OSL) is a well-established and accurate dating technique for mature eolian and fluvial sediments, applications of OSL to glacio-fluvial deposits have remained troublesome. Overestimated luminescence ages of glacio-fluvial sediments have primarily been attributed to inadequate or partial bleaching of sediment in transport due to the attenuation of sunlight through high-suspended sediment concentrations within the water column. Partial bleaching appeared to be the problem with samples collected from Rhône glacio-fluvial deposits in France. Mapped as Late-Würm outwash, the Rhône samples yielded overestimated ages of 75.2 +/- 3.7 to 130.5 +/- 5.4 ka. To investigate the partial bleaching problem and to gain an overall understanding of luminescence characteristics in glacio-fluvial sediments, modern (0-100a) West Greenland sandar were sampled. Sediments from bartop facies were collected to ensure shallow water and thus increased bleaching potential prior to deposition. Other sample characteristics however, such as poor luminescence response, thermal transfer, and feldspar contamination, all of which cause erroneous age-estimates of deposits, also interfered with OSL dating of the West Greenland sediment. Research on these complications, for which there are tests and some corrections, has illuminated additional hurdles and possible triumphs for OSL dating in glacio-fluvial settings. Results of these luminescence tests and corrections, when applied to the Pleistocene glacio-fluvial deposits from the Rhône, could not account for the overestimated ages. Therefore, the Rhône age-overestimates may be attributed to either extreme partial bleaching or suggest that the unit sampled was not latest Würm and additional research in the area must be conducted.