GRAIN SIZE ANALYSIS OF TWO QUATERNARY SECTIONS FROM THE ILLINOIS RIVER VALLEY IN NORTH-CENTRAL ILLINOIS INCLUDING TISKILWA AND BATESTOWN DIAMICTONS OF THE LATE WISCONSINAN WEDRON FORMATION

Two Quaternary sections of glacial deposits along the Illinois River in north-central Illinois were revisited during June, 2004, in order to describe the stratigraphy and collect samples for grain size analyses. The goals of this work are to: 1) correlate the stratigraphy of these sections to nearby sites previously described, 2) expand upon existing knowledge of the processes of subglacial deposition and deformation, and 3) develop a possible local chronology of sediment deposition. The stratigraphy of the Clear Creek and Sister's Sections consist of Tiskilwa and Batestown diamictons of the Late Wisconsinan Wedron Formation, tentatively interpreted as having been deposited by a deforming bed mechanism (Johnson and Hansel, 1999). Diamictons at both sites are overlain by silt and loess. The Clear Creek Section that was sampled consisted of alternating layers of silty and sandy diamicton. Gravel:sand:silt:clay ratios are typically about (2:20:60:18) for the silty layers and (4:40:38:18) for the sandier layers. The Sister's Section has its highest concentrations of sand in the middle (5:55:18:22) with silt-rich diamicton at the top (0:7:83:10) and bottom (0:1:90:9). Sampling procedures tend to underestimate the overall percentage of gravel and coarser material. These initial results indicate significant variability within the same till units at each site. Overall similarities between sites reflect similar parent material and depositional processes, although individual layers are probably not continuous between sites.