Paper No. 44
Presentation Time: 8:30 AM-12:00 PM
MAGNETIC SUSCEPTIBILITY AND FABRIC ANALYSIS FOR GLACIAL TILL DEFORMATION IN THE COAL CREEK SECTION, COAL VALLEY, IL
To understand flow rates of an ice sheet, one must understand the factors controlling these rates. The coupling between an ice sheet and its underlying till can give insight into how the substrate changes due to glacial advancement. Many studies of subglacial till kinematics have involved tedious microstructural analyses coupled with laboratory experiments (e.g. Thomason and Iverson, 2006). Recently demonstrated to be another proxy for strained till, anisotropy of magnetic susceptibility (AMS) has been used in studies of Midwestern tills of the Wisconsin Stage (e.g. Shumway and Iverson, 2009). However, my study involves using AMS on the Kellerville Till of the Illinoian Stage in Rock Island County, IL. Three sites were chosen within a vertical profile of the till exposure. Thirty samples for AMS were obtained from each site by inserting oriented 2.1cm x 2.1cm x 1.7cm boxes into the sediment at each elevation. AMS analyses at Southern Illinois University yielded fabric data. Grain size analyses of samples from each elevation will provide details on sediment types, and 15 orientations of prolate pebbles were measured in the field for corroboration. Although the data collection and interpretation is pending, preliminary conclusions are drawn. The orientations of maximum susceptibility (k1) for each site plot at low angles towards the southeast. Although regional ice flow here was presumably from east to west, there may have been topographic controls on local ice flow directions . Two sites show fairly weak fabrics, while the third site has a stronger fabric. The differing fabric strengths indicate that the strain is probably not consistent through the entire profile, and shearing at each elevation may not have occurred simultaneously.