Poster Number 508
Wednesday, 8 October 2008
George R. Brown Convention Center, Exhibit Hall E
Thousands of ice-walled lake plains occur in northern Illinois and across the glaciated midwestern United States. Pedologic properties related to ice-walled lake plains are poorly documented. The northern Illinois ice-walled lake plains occur in Wisconsin Episode glacigenic and eolian sediments. Ice-walled lake plains range in diameter from 20 m to more than 5 km and typically rise 1 to 8 m above the surrounding loess mantled till surface. These low relief mounds are composed of either a raised border surrounding a low center (“donuts”) or are flat-topped (“pancakes”). Smaller mounds are typically symmetrical while the larger mounds are more elliptical in shape with a long axis trending northeast to southwest. Many of the larger mounds are interpreted to be aggregates of smaller lakes that coalesced as glacial ice stagnated. Modern soil properties are strongly related to mound position and subtle sedimentologic and topographic changes. The typical mound stratigraphy includes subglacial diamicton at the base, less than 1 m of glaciofluvial sands and gravels or debris flow diamicton, 1 to 6 m of fossiliferous, rhythmically bedded lake sediment, 0.3 to 3 m of glaciofluvial sands and gravels or debris flow diamicton, all capped by approximately 1.2 m of loess. The lake sediment is rich in ostracodes and tundra plants. A detailed transect was established across a representative ice-walled lake plain with 2.5 m of relief from mound rim to mound interior. Solum thickness (range = 87 to 160 cm) and loess thickness (range = 63 to 121 cm) were greatest on mound rims and decreased in the mound center. Mound location strongly influenced organic carbon stocks and depth to redoximorphic features. The glacigenic sediment immediately under the loess varied across the mound and had a significant impact on pedogenesis. Understanding glacial sedimentation systems is critical in understanding pedologic relationships on these landforms.