The Pleistocene Geology of Northwestern Iowa

Abstract

248PI,EIBTOCENE GEO~OGY OF NORT~WESTERN IOWA Iowa"/6 which also mapped O'Brien and Clay counties together with parts of Lyon, Osceola, Dickinson, Oherokee and Buena Vista counties as "Wisconsin" lying outside the "Wisconsin Moraine" ' . Su.bsequent work to the south evidently did not bear out the earlier conclusions concerning this extra-morainic Wisconsin area for in the report on Oherokee and Buena Vista counties 17 Cherokee county, to the south of O'Brien, was mapped 'as "Older Drift (Kansan)" except for a triangular area between Mill creek and the Little Sioux which was called '''Wisconsin Overwash Gravel" (figure 27) . . The west part of Buena Vista county also was mapped as Kansan drift, which consequently abl1t;. on the north against the ';Wisconsin Drift'" area of the Clay county map. The central and east parts of Buena Vista county were mapped as '~Wisconsin Drift",. but without a morainic belt ~i.long the boundary. . The . prevIous assignment of the drift of O'Brien and Clay counties to the Wisconsin epoch was questioned (page 319), with the suggestion that it might prove to be earlier Wisconsin or even older. The problem was evidently considered the same as that in Plymouth connty to which report "the reader is referred." In the' Plymouth .county report the drift had been provisionally referred to the Iowan epoch. l8 As a part of the report on Oherokee and Buena Vista counties P.rofessor Macbride discussed "The Margin of the \ Wisconsin Drift')19 in northwestern Iowa, and mapped the course of 1 the Altamont moraine (figure 28), a course which shows little relation to that of the same moraine on the county maps north of .

Chronology and provenance of last-glacial (peoria) loess in western iowa and paleoclimatic implications

“…Ruhe (1983) offered two explanations for these differences: (1) the oldest Peoria Loess was derived from a non-calcareous (and possibly non-glacial) source and (2) the lower zones were subjected to syndepositional leaching during an initial period of slower loess sedimentation. It has long been thought that Peoria Loess in western Iowa was derived from outwash on the Missouri River floodplain during the last glacial period (Carman, 1917;Kay and Apfel, 1929;Carman, 1931;Simonson and Hutton, 1954;Ruhe, 1969Ruhe, , 1983. Loess thins eastward from the Missouri River floodplain, displaying decreases in thickness that can be described mathematically (Ruhe, 1954;Muhs and Bettis, 2000).…”

History of Investigation and Classification of Wisconsinan Drift in North-Central United States

“…It may be noted that Carman (1917) explained the "Iowan drift" in northwestern Iowa as eroded Kansas till. Like Ruhe's explanation for eastern Iowa 50 years later, he suggested that erosion had truncated drift of two different ages.…”

“…The idea was so revolutionary that it was not allowed to be printed by the Iowa State Geologist until it was considerably modified (Kay and Apfel, 1929, p. 114). Later, Carman's ideas were more acceptable, particularly about the two ages of the drift, and were printed in a revision of his earlier bulletin (Carman, 1931).…”

Eutrophication of some northwestern Iowa lakes

“…The Iowa Great Lakes watershed is located in three town ships of north-central Dickinson County, Iowa and extends into four townships of Jackson County, Minnesota (Figure 1). The lake system lies in the Cary drift of the Des Moines lobe and is enclosed by morainal topography (Thomas, 1913;Tilton, 1916;Carman, 1917). Radiocarbon dating of lake sediments indicates a late Cary or a postglacial age for the lake basin (Dodd et , 1968…”