Deglacial History and Paleoenvironments of Northeastern Illinois

TroyRockWINNEBAGOBOONE MCHENRY LAKELakeMichiganOGLEDEKALBKANECOOKDUPAGELEESt. CharlesKENDALLWILLBUREAULASALLEGRUNDYPUTNAMTiconaKANKAKEEFigure 8 Shaded relief map of the bedrock topography of northeastern Illinois based on the map of Herzoget al. (1994) and data from Luman et al. (2003). Map courtesy of Curt Abert, ISGS. .On the X-ray diffractograms, the spacings for the groups above are measured at 5.1, 8.8, and12.4˚2 respectively; correction factors of 1.4, 4.0, and 1.8 are applied, respectively, in order tocalculate relative percentages of each group (Hughes et al., 1994).In more recent studies, the ISGS has been estimating kaolinite and chlorite percentages by applyingthe peak height ratio measured at 24.9˚2 and 25.1˚2 for kaolinite and chlorite, respectively,to the peak measured at 12.4˚2 (e.g., Curry and Grimley, 2006). We have found the individualmeasurements of kaolinite and chlorite to be useful in characterizing loess units in northeasternIllinois, but less useful for helping to differentiate among diamicton units of the WedronFormation. Relative calcite and dolomite content of the < 0.002 mm fraction were measured bypeak height (counts per second) on the XRD diffractograms. In some studies, we have estimatedthe relative content of quartz, plagioclase, and potassium feldspar from X-ray diffractograms(e.g., Curry and Grimley, 2006). Another useful parameter in characterizing stratigraphic unitsand identifying weathering horizons is the diffraction intensity ratio (DI). The DI is the ratio of the13