Petrographic and geochemical analysis of detrital magnetite in late Wisconsinan tills in eastern Indiana and western Ohio

Detrital magnetite, although averaging less than I% of till volume, is a common constituent in glacial tills of eastern Indiana and western Ohio. Because of its abundance and ease of sampling, detrital magnetite was chosen to determine its potential as a tool to 1) determine provenance of the glacial tills and 2) to chemically fingerprint glacial sedimentary deposits for use in stratigraphic analysis. Two sampling programs were performed. First, glacial till samples were collected from a vertical section in western Ohio at the location of Doty's High Bank. Second, glacial tills were collected from a lateral distribution of five moraines in northeast and east central Indiana.Petrographic analysis of 946 detrital magnetite grains from eastern Indiana and western Ohio has shown that 81% of the magnetite grains are homogeneous, 15% have magnetite-ilmenite intergrowths, and 4% have exsolved phases of ulvospinel/pleonaste.Eighteen percent of all detrital magnetite grains have some level of hematite alteration. Chemical analyses were performed on 403 homogeneous detrital magnetite grains. These grains were analyzed for Fe, Ti, Mg, Mn, Cr, V, Al, and Si. The means and standard deviations of these eight elements, in weight percent oxide, are FeO (89.8087.696), TiO2 (1.58 ± 4.99), MgO ( 0.052 ± 0.200), MnO ( 0.172 ± 0.284), Cr2O3 (0.1942.256), V2O3 ( 0.241 ± 0.245), Al2O3 (0.455 ± 1.234), and SiO2 ( 0.035 ± 0.047).A Canadian source north of Lake Huron and south of James Bay is suggested based on previous studies of flow directions of the Laurentide Ice Sheet and bedrock geology in southern Canada. The bedrock in this area is primarily felsic plutonic and mafic volcanic. The petrographic and geochemical results of this study indicate this area as the source area for the detrital magnetite in eastern Indiana and western Ohio tills. Chemical fingerprints based on cluster analysis and bivariate plots were found within the vertical exposure of Doty's High Bank and the lateral moraines of eastern Indiana. Samples from the Muncie esker (unknown age) were found to correlate with the southernmost set of eastern Indiana moraines based on the chemical fingerprint analysis.Department of GeologyThesis (M.S.