TRACE ELEMENT GEOCHEMISTRY OF SLACKWATER SEDIMENTS IN THE SAVANNA TERRACE, SAVANNA, IL

The Savanna Terrace is an area alongside the Upper Mississippi River and was formed during the Late Wisconsin Episode of the Laurentide Ice Sheet (LIS). Drainage from the LIS flowed down the Mississippi River which created blockage within tributaries causing deposition of sediments in slackwater terraces. The field site for this study is 8 km north of Savanna, Illinois. In this region, the slackwater clay terrace is composed of alternating red and gray sediment deposits of the Equality Formation. This research attempts to link the gray slackwater sediments to the Des Moines Lobe. The redness, particle size and clay mineralogy of the gray sediment’s trace elements were compared to samples from the Des Moines Lobe. Trace element analysis was conducted using an ICP-MS in order to compare the Des Moines Lobe to the terrace sediments in the field area. Early research conducted by Johnson (2009) shows that the gray terrace sediments contain large amounts of Se and Cd and its clay minerals have a comparative percentage of 69% ± 4% expandable clay minerals from the smectite group, 19% ± 3% illite, and 12 ± 3% of kaolinite plus chlorite.