A near synthesis of pre-Illinoian till stratigraphy in the central United States: Iowa, Nebraska and Missouri
Nearly identical sequences of pre-Illinoian glacial till are present throughout the north-central United States in Iowa, Nebraska and Missouri. In each of these states three tills with normal magnetic remanence have been found above two - three tills with reversed remanence, and the lithologic differences among successive tills are nearly the same. Each till is capped by a mature paleosol, except for the two youngest reversed-polarity tills, which are nearly identical in lithology and separated by immature weathering profiles. These results seem to indicate that deposits from five major pre-Illinoian glaciations are present throughout this entire region.
Cosmogenic-nuclide burial ages provide relatively precise ages for the three earliest glaciations that reached northeast Missouri: ca. 2.4, 1.3 and 0.76 Ma. Ages of the youngest two glaciations in this area are less precise, but both are between ∼0.2 and 0.4 Ma. The tills in Nebraska and western Iowa have not been dated directly, but are constrained by the ages of interbedded tephra, and these limits are consistent with the burial ages in Missouri for tills in the same relative stratigraphic positions, with one exception. Two of the three normal-polarity tills in Nebraska/western Iowa are present below the 0.64 Ma Lava Creek B tephra, and thus should be between 0.64 and 0.78 Ma in age. However, only one of the normal-polarity tills in northeast Missouri is within this range. This discrepancy indicates either a problem with the age constraints or that the till sequence is more complex than yet recognized.
Geography, Geology, and Planning
rre-Illinoian tills, Missouri, Nebraska, Iowa, burial dating
Rovey II, C. W., and Trevor McLouth. "A near synthesis of pre-Illinoian till stratigraphy in the central United States: Iowa, Nebraska and Missouri." Quaternary Science Reviews 126 (2015): 96-111.
Quaternary Science Reviews