OSL DATING OF GLACIAL LAKE AGASSIZ STRANDLINES IN WESTERN CASS COUNTY, NORTH DAKOTA

Freshwater releases from glacial Lake Agassiz may have served as a trigger for abrupt climate change at the close of the Pleistocene. Lake Agassiz strandlines preserve paleo-water level records that are critical to understanding the volume and timing of potential freshwater releases; however, chronologic controls for the strandlines are limited or lacking. Optically Stimulated Luminescence (OSL) dating provides a means to directly determine the depositional age of glacial Lake Agassiz beach ridges. This study is concerned with an area of multiple NNE trending linear features located in western Cass County, North Dakota that are interpreted as Lake Agassiz strandlines. The four most topographically prominent strandlines along a five mile transect of Cass County Hwy 10 were sampled for OSL dating. In addition to topographic expression, soil classification mapping was used to identify sample sites as detailed by Brevik and Fenton (Paleolim. 22:253-257, 1999). Based on elevation and latitude, these four strandlines can be correlated with the Herman, Norcross, Tintah, and Campbell beach ridges (Teller and Thorleifson, Geol. Assc. Can. Spec. Pap. 26:261-290, 1983). Two grain-size fractions (vfs: 90-150µm and fs:150-250µm) from each sample site were dated using single-aliquot regenerative dose data collection procedures as well as dose distribution analysis methods. This presentation will compare the dating results from the two grain-size fractions along with geomorphic and physiographic attributes of the study area. The depositional ages obtained for the Herman and Norcross ridges are consistent with work done by Lepper et al. (Geology 35:667-670, 2007) on beach ridges at the southern outlet of glacial Lake Agassiz.