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The Chariton Conglomerate is a quartz limestone conglomerate of Pennsylvanian age found in six exposures in southern Iowa and three exposures in northern Missouri. Distinctive features of the exposures in Iowa include quartz granules and rounded crinoid columnals. The objective of this study was to determine whether the quartz clasts could have originated in the crystalline rocks of Minnesota or Wisconsin. The average paleocurrent direction measured in interbedded sandstones was 178° (S.D. = 35 °). The average roundness of 75 crinoid columnals extracted from four exposures in Iowa was 30% (S.D. = 14%), defined as

roundness(%) = (D-d)/D x 100,

where D is the maximum columnal diameter and d is the diameter of the flat circle at the end of the columnal. Previously unabtaded crinoid columnals were abraded in rotary tumblers, which were filled 90% with water and 10% with a mixture representative of the Chariton Conglomerate. The roundness values of the experimentally abraded columnals were consistent with the roundness values of the columnals collected in the field (within one standard deviation of the mean for the field data) for tumbling times in the range 0-33 days. Assuming the travel distance corresponding ro one revolution is the circumference of the barrel, the experimental roundness values were consistent with the field roundness values for travel distances in the range 0-700 km, which is sufficiently far to include the crystalline rocks of Minnesota and Wisconsin.

Publication Date

January-December 2007

Journal Title

Journal of the Iowa Academy of Science





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© Copyright 2008 by the Iowa Academy of Science, Inc.



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