Early middle Pleistocene glacial sediments (780000‐620000 BP) near Kansas City, northeastern Kansas and northwestern Missouri, USA

Abstract

Colgan, P. M. 1999 (December): Early middle Pleistocene glacial sediments (780 000-620 OOO BP) near Kansas City, northeastem Kansas and northwestern Missouri, USA. Boreas, VoI. 28, pp. 477489. Oslo. ISSN Two lithologically distinct tills are present near the pre-Illinoian glacial boundary in northeastern Kansas and northwestern Missouri. The tills are probably early middle Pleistocene (780 000-620 OOO BP) based on normal polarity and their stratigraphic relationship to dated terraces. The upper till is sandier than the lower till and contains more expandable clay minerals and less illite than the lower till. Glaciofluvial and supraglacial sediments are preserved between the tills, yet palaeosols, or other evidence of an interglacial, are not present, suggesting that the tills were deposited during a single glaciation. Southeasterly and southwesterly trending striae and till fabric suggest that the glacial succession was deposited by at least two fluctuations (phases) of a lobe, which probably advanced down the axis of the present Missouri River lowland. These tills probably correlate to early middle Pleistocene tills in southwestern Iowa and eastern Nebraska, although it is possible that the lower till may correlate to even older tills in these areas.BOREAS 0300-9483.

Insights into the late Cenozoic configuration of the Laurentide Ice Sheet from40Ar/39Ar dating of glacially transported minerals in midcontinent tills

“…Four samples are late Pliocene R2 tills, four samples are early Pleistocene R1 tills, five samples are middle Pleistocene N tills, and one sample is associated with the LGM. These till units were chosen because they were representative of the regional trend in compositional variations described above [ Boellstorff , 1978; Aber , 1991; Rovey and Kean , 1996; Colgan , 1999; Roy et al , 2004a]. Table 1 shows the position of each till unit in the stratigraphic section sampled.…”

“…The midcontinent glacial record also exhibits a systematic compositional change through time consisting of older tills enriched in sedimentary clasts, quartz, and kaolinite to younger tills enriched in crystalline clasts, feldspar, and expandable (mixed‐layered) clays [ Boellstorff , 1978; Aber , 1991; Rovey and Kean , 1996; Colgan , 1999; Roy et al , 2004a]. These till compositional changes may record a change in provenance associated with the erosion of multiple rock‐source regions of varying bedrock composition.…”