Paleoclimatic Interpretation of the Moorhead Low Water Phase of Glacial Lake Agassiz in the Southern Basin based on Fossil Coleoptera Assemblages
Rock, Jessie Lee
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See submission document for full abstract.Detrital peats of the Poplar River Formation were deposited in the Lake Agassiz basin during the Moorhead Low Water Phase (MLWP). Two new fossil sites, in Moorhead, Minnesota (MS28) and Fargo, North Dakota (UPC), provide a wealth of information about the chronology, paleoenvironment, and paleoclimate of the southern basin of lake Agassiz. Sediments at both sites were deposited as part of a delta which prograded into Lake Agassiz. The insect and plant taxa represent a biological community that existed during a time when the southern basin of Lake Agassiz experienced subaerial exposure. Eight AMS radiocarbon dates were obtained from these deposits and range from 11,178 ± 49 cal yr BP (9,737 ± 53 ^14C yr BP) to 11,467 ± 107 cal yr BP (10,011 ± 35 ^14C yr BP). The large number of insect and plant taxa identified from fossils at the sites indicates that the environment was a biologically rich, complex wetland that developed in situ on the delta top. This wetland included rivers, ponds, marshes, and swamps and supported wooded areas with stands of Picea (spruce), Larix laricina (larch), Salix (willow), and Populus (poplar). The paleotemperature in the Fargo-Moorhead region during the MLWP, based on a modified Mutual Climatic Range analysis, had a mean July temperature of l7°C, approximately 4°C cooler than the region at the present day. This estimate of mean July temperature is at least 2°C lower than previous estimates.