HEAVY MINERAL ANALYSIS OF GLACIAL TILL IN NORTHERN AND SOUTH-CENTRAL INDIANA TO RECONSTRUCT PATH OF GLACIAL ICE

The path of the Laurentide Ice Sheet has not been thoroughly explored in Indiana with respect to which lobes, Michigan, Huron-Erie, and Saginaw flowed through the area. Heavy minerals as a means of differentiating between these lobes has been successful across the upper Great Lakes in Michigan and Ontario, but has not been applied in Indiana. For example, Gwyn and Dreimanis (1979) used the relative proportions of heavy minerals within the drift of the southern Canadian Shield, to map compositional variations in till within and between the Superior and Grenville provinces. Similarly, Dworkin et al. (1985) used the relative proportions of heavy minerals in tills from the three lobes in Michigan and determined that heavy minerals could distinguish the lobes as well as their specific provenances: Huron-Erie lobe derived from the Grenville province, Saginaw lobe derived from the boundary between the Grenville and Superior provinces, and Michigan lobe derived from the Superior province.

Heavy minerals from the 250-125 micron sand size in tills from cores and exposures in northern and southern-central Indiana were separated and point counted to create relative percentages of heavy minerals. Preliminary results show that tills from the Michigan and Huron-Erie lobes could be differentiated using heavy minerals. Possible Saginaw lobe samples, however, could not and had assemblages similar to the Huron-Erie lobe. Heavy mineral assemblages of till samples from near the terminal moraine in southern Indiana were consistent with other Huron-Erie lobe tills from northern Indiana. Samples were also collected from beyond the Laurentide Ice Sheet terminal moraine in an effort to find a similar correlation in pre-Wisconsinan tills.

The preliminary results of this study indicate that heavy mineral assemblages can differentiate between lobes of the Laurentide Ice Sheet in Indiana. Because till in south-central Indiana was likely from the Huron-Erie lobe, this lobe was probably more dominant across much of Indiana south and east of the Wabash River. Its southern margin may have been the ice front that deposited the terminal moraine in Indiana. Heavy minerals may also prove useful to determine provenance of pre-Wisconsinan tills and test whether the path of older ice sheets were the same or different than during the late Wisconsinan.