LAKE AGASSIZ BEACH MAMMOTHS: NEW DATES FOR SOME OLD BEACH BUMS

Remains of at least four mammoths have been recovered from Herman stage beach deposits of Glacial Lake Agassiz in North Dakota and Minnesota. These discoveries were reported in the scientific literature between 1895 and 1986. Geologic ages for these mammoths are either non-existent or were assigned, based simply on their context, as equivalent to the age of the Herman beach. My laboratory has been successful in applying optically stimulated luminescence (OSL) dating methods to Lake Agassiz beach deposits. Because of these successes and the enthusiasm generated by the hairy, hulking proboscideans, I have been able to involve several students over the past few years in researching the mammoth discovery sites, revisiting them, collecting samples of beach ridge sediments, and conducting laboratory work for OSL dating. This presentation will review the rediscovery process, the nature of the fossils and their current disposition, if known, as well as present direct contextual ages determined by OSL dating for the deposits at or very near the specimen recovery locations. Our age results range from 14.0 ± 0.3 ka to 14.3 ± 0.3 ka, with a very high degree of inter-sample consistency (indistinguishable at the ± 1 std err level). These results demonstrate that OSL dating can be used to help strengthen the correlation of Herman beach deposits over great distances. The results also indicate the potential utility of OSL dating to help correlate other beach ridge complexes of Lake Agassiz over similarly large distances.