In the Rochester section, the Sangamon Soil is developed directly in Illinoian glacial till and overlain by Roxana Silt, the oldest of the two regional Wisconsinan loesses.
[2][4][5] Although it includes the same time span, the Sangamonian Stage (sensu lato) is not temporally equivalent to the Eemian in Europe.
In its much less common usage, the Sangamonian Stage (sensu stricto) is equivalent to Marine Isotope Substage 5e and the Eemian.
[2][4][3] The start of the Sangamonian Stage is constrained by optically stimulated luminescence (OSL) dates obtained from fluvial deposits of the Pearl Formation and Illinoian glacial tills of the Glasford Formation, which fill an ancient and buried Mississippi River valley in north-central Illinois.
The age of fluvial sediments overlying the youngest glacial till (Radnor Member) of the Glasford Formation yield optically stimulated luminescence (OSL) dates that averaged 131,000 BP.