QUANTIFYING MAGNETIC FLY ASH IN POST-SETTLEMENT ALLUVIUM FROM THE SANGAMON RIVER BASIN, ILLINOIS

Since the beginning of European settlement in the mid-1800’s in central Illinois, much of the postglacial landscape has been altered by anthropogenic activity. Studying the alluvium deposited in the Sangamon River floodplain can give scientists insight into the change of deposition rate in which industrialization has brought to this landscape. This study examines the characteristics of the magnetic content from coal use in post-settlement alluvium (PSA) in the Sangamon River floodplain in central Illinois. The methodology includes examining hand auger samples up to 1 to 1.5 meters deep from three sites in the Sangamon River valley. This study uses fly ash particles (magnetic spherules) produced from coal combustion and coal engines as markers throughout the alluvium samples. Magnetic particles are extracted and purified from core samples and examined under the microscope to try to provide a basis to identify PSA from pre-settlement alluvium (where there should be little to no fly ash particles) based on fly ash percentages. From each core sample, a hundred particles were counted to determine fly ash percentages at intervals of 10 centimeters. Results from the latest cores from Lake of the Woods and Allerton Park floodplains show that there is a sharp decrease in percentages of fly ash at approximately 60 to 70 cm depths, indicating that the upper 70 cm of alluvium was deposited after European settlement. Data also show a decrease in fly ash in the upper level of PSA which can suggests a correlation to the implementation of the Clean Air Act in the 1970’s. Further research is expected from examination of Cs-137 and Pb-210 dating tests of soil samples to better understand and confirm the chronology based on fly ash percentages.