Illinoian

A glacial stage of the Quaternary in North America, followed by the Sangamon Interglacial and following the Yarmouth. The Illinoian ice sheet covered a small area of southeastern and extreme eastern Iowa, and in so doing it diverted the Mississippi River and created a valley along its western front that can still be seen. It consists mainly of tills, the products of large ice-sheets, and has been split up into three sub-stages, the Liman, Monican, and Jubileean. It is unclear how many cold stages the Illinoian deposits represent, but it may be more than one. The Illinoian Glacial Stage ended with a cool, moist period that gradually became drier and then warmer. The Illinoian has never been dated satisfactorily but it is roughly contemporary with the Riss and Saale Glacial Periods.

Group of Quaternary glacial deposits in North America; covered by the Sangamon soil and burying Yarmouth palaeosols (see Table 7, page 420). It consists mainly of tills, the products of large icesheets, and has been split up into three substages, the Liman, Monican and Jubileean. Tills of the Liman and Monican sub-stages are separated by a palaeosol, the Pike soil, which may represent either an interstadial or an interglacial. A much more weakly developed soil separates the Monican from the Jubileean. It is unclear how many cold stages the Illinoian deposits represent, but it may be more than one. The Illinoian has never been dated satisfactorily.