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

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.