Late Quaternary history and paleoecology of a small oxbow wetland on glaciated terrain were investigated using sediment lithology (cores, bulk samples, backhoedug trenches), ground-penetrating radar, vascular plant and moss macrofossil stratigraphies, and accelerator mass spectrometric radiocarbon dating. A nearly complete mastodon skeleton was recovered from late Pleistocene detrital peat and peaty marl near the top of the sediment sequence. Sedimentation in the basin began with silt and clay over dense cobble outwash transported southward from the nearby Hyde Park Moraine. Overbank sediment deposition occurred between ∼13,000 and 12,220 yr B.P. during a period of tundra vegetation, which ended with a sharp rise in spruce needle abundance and a shift to autochthonous marl and finally peat deposition. Fossils of aquatic and wetland plants began to accumulate before the tundra-spruce transition and increased after it. Rich fen wetland began to infill the pond with peat, while the upland supported open white spruce and later white spruce–balsam fir–tamarack forest. The mastodon, 11,480 ± 40 radiocarbon years old, was contemporaneous with spruce–balsam fir–tamarack forest and rich fen wetland. Many mastodon bones were articulated or nearly so, indicating that the animal died in the basin and that postmortem bone dispersal was slight.

Fourteen consecutive field seasons of scientific excavations of alluvial deposits of the lower Pomme de Terre Valley, southeastern Missouri, have provided a radiocarbondated (154 analyses) chronostratigraphic sequence in four terraces reflecting five major episodes of aggradation and degradation. Probably all of Wisconsinan time and the Holocene is represented. A sixth alluvial deposit is probably Illinoian and possibly older Pleistocene alluvium. Spring deposits within the terraces contain bone beds associated with peat lenses containing pollen, plant, and beetle remains, all of which have provided paleoecological data. The springs appear to have erupted initially, in response to either tectonic disturbance or hydrostatic pressure near the peak of a glacial maximum. Subsequent episodes may correlate with later maxima. Peat deposits correlate with interstadials on the bases of fauna, flora, and radiocarbon dating. Gravel deposits of spring conduits contain bones and plant remains that are considerably older than overlying peat deposits. Some of these older elements have been redeposited in younger spring deposits via spring action. Other evidence suggests that some animals may have fallen into springs and intruded older deposits. A developmental sequence for the origin of concentric spring deposits in alluvium is proposed. None of the six spring deposits excavated contained any associated archaeological remains older than 10,500 B.P., which marks the first appearance of artifacts in the stratigraphic record at Rodgers Shelter. Extinction of the Pleistocene big-game animals occurred sometime between then and 16,000 B.P. A major episode of degradation occurring between 10,500 and 13,000 B.P. probably coincides with similar episodes occurring approximately 12,000 B.P. on many if not most streams in the United States. With some exceptions, subsequent epicycles of cutting and filling appear to correlate generally over the same area.