Questioning the age of the Moorhead Phase in the glacial Lake Agassiz basin

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The stratigraphy of sites within the Lake Agassiz basin that constrain the timing of the onset of the Moorhead low-water Phase is reexamined. Stratigraphic interpretation of the oldest date (10,960 14C yr BP) from cross-bedded sand of the Ojata Beach is questioned, particularly in light of demonstrated long-distance transport and reworking of older organic material from elsewhere in the basin. A maximum onset age for the Moorhead Phase is suggested from a 10,675±60 14C yr BP age from wood in gravel from the base of the southern outlet, whereas radiocarbon dates from in situ peat indicate a later minimum onset age of 10,340±100 14C BP.