The only formal morphostratigraphic units recognized in IL are units related to moraines that are called "drifts." Is named for the village of Turpin, 3 mi southeast of Decatur, Macon Co, IL (Illinois basin); is based on the Turpin Moraine (mapped on pl. 1), a sharp morainic ridge about 6 mi long and 1 to 2 mi wide, with a relief of 25 to 50 ft, that extends northeast from Turpin to the front of the Cerro Gordo Moraine. The ridge may mark a temporary stand of the ice front during retreat from the Shelbyville Moraine. However, its orientation normal to the Shelbyville and Cerro Gordo Moraines suggests that it may be a ridge on the Illinoian till plain mantled by Shelbyville Drift, and, if further study indicates that this is the case, the term Turpin Drift will not be needed. Deposited by the Decatur Sublobe of the Erie Lobe. Assigned to Woodfordian Substage of Wisconsinan Stage in Pleistocene Series.

Source: GNU records (USGS DDS-6; Denver GNULEX).