Additional Information on Clays in Pleistocene Deposits of Northeastern Kansas

Abstract

In a previous study (Tien, 1968), relative intensities of first reflections of mixed-layer mineral, illite and kaolinite, and the diffraction intensity (D.I.) ratio of illite to kaolinite were used to differentiate stratigraphic units of till and nontill deposits. At least two Kansan tills could be distinguished. Associated nontill deposits could not be subdivided into meaningful stratigraphic groups. On the basis of 74 samples from southeastern Doniphan County, it was concluded that claymineral assemblages are diagnostic features of Pleistocene deposits, and that further sampling would not alter the results. A new road cut, 0.4 mile north of SWc sec. 33, T.8 S., R.19 E., along US Highway 59, 6 miles north of Oskaloosa, Jefferson County, Kansas (Fig. 1) offers not only an opportunity for additional information on clays of Pleistocene deposits, but also for testing the conclusions made from the previous study. The purpose of this note is (1) to present the results of X-ray diffraction studies on samples from this new road cut, and (2) to discuss the significance of these results to correlate Pleistocene deposits by use of clay minerals in northeastern Kansas. Twelve samples (noting relative stratigraphic position and lithology) were collected from the road cut. The samples were analyzed in the same manner as those used in the previous study (Tien, 1968, p. 99-100). Results of X-ray diffraction analyses of the less than 2 micron fraction and stratigraphic position of samples are listed in Table 1. Each of the 12 samples was plotted on the ternary diagram in terms of the relative intensities of the first basal reflections of the three principal clay minerals. Those samples studied previously were plotted also for comparison (Fig. 2). It was found that the clay-mineral assemblages in the samples from this new road cut were identical to those in samples previously studied. All three till samples had a low D.I. ratio (less than 0.50) of illite to kaolinite. Relative intensities of the first basal reflections of kaolinite, mixed-layer mineral, and illite ranged from 15 to 17, 75 to 79, and 6 to 8 respectively. The nontill samples had a D.I. ratio of illite to kaolinite ranging from 1.11 to 1.82, and the intensities of the first basal