PRE-ILLINOIAN GLACIATION BOUNDARY AT KANSAS CITY, MISSOURI

Isolated deposits of glacial till (diamicton) at four locations south of the Missouri River are evidence that a pre-Illinoian glacial lobe crossed the ancestral Kansas River and moved southward into Kansas City, Missouri. The ice lobe blocked the river, forming ice-margin lakes that became diverted through outlet channels into the Lower Turkey Creek Valley and the Lower Little Blue River Valley creating diversional spillways around the ice front. The section of alluvium in the Missouri River Valley is 100-150 ft thick but increases to ~200 ft in deep, narrow trenches eroded into the bedrock channel floor. A narrow trench ~50ft deep and a few hundred ft wide was penetrated in boreholes along the route for construction of the Trans-Missouri River Water Tunnel (TMRT)in 1989. Glacial till was encountered in the lower several feet of the deep trench at an elevation of 550 ft M.S.L. The difference in elevation of the till in the "buried" bedrock trench and the highest glacial till at Downtown Kansas City is 400 ft, an indication of the minimum thickness of the ice sheet, assuming that the till at the two places was deposited by the same ice lobe. The till-filled, deep trench is not an isolated occurrence. Glacial till was logged in boreholes at the bottom of a deep trench in the Kansas River Valley near confluence with the Missouri River. Theories for the origin of the deep trenches include among others: (a)subglacial streams eroding into soft shale beneath an ice sheet, (b) large volumes of meltwater flowing along the margins of an ice sheet, (c)isostatic uplift adjecent to an advancing glacier and, (d)regional stream rejuvenation due to sea-level lowering. An extraordinary section of Pleistocene glacial drift and loess was well-exposed in 1999 on the north bluff of the Missouri River. Two units of pre-Illinoian glaciogenic sediment deposits separated by a paleosol are an indication that there were two glacial advances, raising the possibility that the Dakota and the Minnesota ice lobes reached Kansas City.