NEW INSIGHTS INTO THE AGE AND GEOLOGICAL CONTEXT OF THE WALHALLA NORTH DAKOTA MAMMOTH

Glacial Lake Agassiz was formed ~14,000 years ago during the recession of the Laurentide Ice Sheet in North America. Over time, this massive lake deposited a series a beach ridges as the water level receded to the north. Within these ridges, several different fossils have been discovered including the remains of mammoths. The Herman beach ridge is the earliest of the well-developed ridges of Lake Agassiz and four mammoth specimens have reportedly been found in association with this ridge but none have been documented from younger ridges. One of the four specimens was found near Walhalla, North Dakota but during examination of past scientific records, we have been left with a discrepancy in the location of the site at which it was found. One reported location would place the fossil within floodplain deposits along the Pembina River, in which case the river would have reworked the fossil, therefore making its stratigraphic connection to Lake Agassiz impossible. The other location is consistent with a Lake Agassiz beach ridge deposit, however, our analysis suggests that this ridge correlates with the Norcross, in which case, the Walhalla mammoth would stratigraphically be the youngest Agassiz beach mammoth ever found. Sediment samples from the beach ridge site have been collected and preparations for OSL dating are underway. Determining the geologic context for this mammoth is vital to establishing if this specimen should be considered a genuine “beach mammoth” and if so, its depositional age will be important in understanding the relation of this beach mammoth with others across the glacial lake beach system.