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|Title:||Late Pleistocene and Holocene landscape evolution, depositional subsystems, and stratigraphy in the lower Illinois River Valley and adjacent central Mississippi River Valley|
|Author(s):||Hajic, Edwin Robert|
|Doctoral Committee Chair(s):||Johnson, W. Hilton|
|Department / Program:||Geology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The Illinois Valley is a critical link between major late Pleistocene geomorphic systems in the central United States.
A late Farmdalian--early Woodfordian glaciofluvial--catastrophic flood subsystem was characterized by (1) early aggradation on the order of 20-25 m between about 26,000 and 19,500 B.P. in response to glaciation in the upper Mississippi Valley; (2) drainage diversion of the Mississippi River to its present valley about 19,500 B.P. and reworking and net incision of the valley train in the Illinois Valley for the remainder of the late Woodfordian as the Lake Michigan Lobe downwasted and retreated; (3) catastrophic glacial lake outburst floods ("Kankakee Torrent") between 16,000 and 15,500 B.P. triggered by large influx into proglacial lakes of meltwater from a subglacial reservoir in the Lake Michigan Basin during the Haeger glacial phase of the Lake Michigan Lobe.
A terminal Woodfordian lacustrine subsystem existed in the Illinois Valley and other central Mississippi Valley tributaries between about 13,400 and 12,200 B.P.
Following an episode of very early Holocene (9800-9700 B.P.) incision and terrace formation in response to downcutting in the Mississippi Valley caused by the latest discharge from Lake Agassiz, and an initial phase of lacustrine sedimentation in a valley-wide lake in response to Mississippi Valley fluctuations, the Illinois River developed a set of natural levees at about the altitude of modern natural levees. During the remainder of the Holocene, the Illinois River remained a sluggish stable river of small sinuosity and gradient under the combined influence of inheritance of an incised channel of small sinuosity, backflooding and aggradation by the Mississippi River, cohesive bank material, and possibly favorable crustal tilting. Broad valley areas below terraces evolved from relatively deep perennial lateral lakes to emergent floodplains between about 8500 and 3000 B.P. as material derived from extensive erosion of loess off the surrounding uplands was deposited in valley lakes and alluvial fans. Many tributary and main valley landscape components were modified by a brief period of increased runoff and flooding between 3000 and 2500 B.P. Shallow semi-permanent and intermittent backwater lakes with limited overbank sedimentation characterized the very latest Holocene valley environments. (Abstract shortened with permission of author.)
|Rights Information:||Copyright 1990 Hajic, Edwin Robert|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9021692|
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