What is Luminescence? Optically Stimulated Luminescence (OSL) Sediment Context Collection Procedures

Late Pleistocene luminescence chronology of loess deposition

Missouri and Mississippi river valleys, United States

luminescence graph

The loess stratigraphy of the mid-continental U.S. is an important proxy record for the advance of the North American ice sheet into the catchment of the Mississippi, Missouri and Ohio rivers. One of the most outstanding problems is deciphering the age of loess deposits in this area during the late Pleistocene. We used multiple-aliquot additive-dose procedures under infrared stimulated luminescence (IRSL) and single aliquot regeneration (SAR) protocals to resolve ages of loess at the Loveland Silt type locality, Iowa, the Pleasant Grove School section, Illinois and the Bonfils Quarry section, Missouri. Radiocarbon dated levels in the Peoria Loess and Roxana Silt were used to test the accuracy of IRSL and SAR methods. SAR on polymineral and quartz extracts yielded underestimates in age by 20 to 55%, whereas IRSL gave concordant ages to the 14C control and was used to date the loess sequences. The oldest loess, the Bonfils Silt, gave IRSL ages between 159 ka and 264 ka and are considered nonfinite estimates because the luminescence response was near saturation with additive beta dose. The Loveland Silt at the type locality exhibited considerable luminescence in growth with additive beta dose and yielded the mean age of 159 14 ka (n= 4). The Teneriffe Silt gave a mean IRSL age of 93 5 ka (n=4) which, overlaps at two sigma with a previous TL age and indicates deposition sometime between 100 and 80 ka. The Roxana Silt yielded stratigraphically consistent IRSL ages between c. 60 ka and 30 ka. Luminescence and radiocarbon dating indicate that there were four distinct periods of loess deposition in the Mississippi and Missouri River basins at c. 180 to 140 ka, 100 to 80 ka, 60 to 30 ka, and 25 to 12 ka which are concordant with periods of meltwater input to the Gulf of Mexico, another proxy of glaciation in mid-continental North America.
S. L. Forman, J. Pierson and E. A. Bettis III (Univ of Iowa, Iowa City)