Quaternary stratigraphy of the lower Iowa and Cedar River Valleys, southeast Iowa

This study investigates the extensive terraces along the lower Iowa and Cedar Rivers, southeastern Iowa. Three stratigraphically distinct terrace systems are recognized and designated (with decreasing age), the Early Phase High Terrace (EPHT), Late Phase High Terrace (LPHT), and Low Terrace (LT) systems. Previous investigations attributed EPHT and LPHT deposits along the Iowa River and LT deposits along the Cedar River to the hypothetical, Illinoian, proglacial Lake Calvin. However, these terraces are composed of alluvium overlain by Wisconsinan and Holocene eolian and colluvial deposits which are too young to be associated with an Illinoian lake. There is no stratigraphic or sedimentologic evidence that supports the existence of Lake Calvin. Loess, eolian sand, and local alluvial and colluvial facies, totalling 6 - 9 m thick, mantles the EPHT. A buried incipient soil, which dates at circa 17,000 - 21,000 Y.B.P. is developed at the base of this surficial package.