3-D GLACIAL MAPPING OF THE LAWRENCE 7.5 MINUTE QUADRANGLE, VAN BUREN COUNTY, SOUTHWEST MICHIGAN

Results of a recently completed STATEMAP Project for the Lawrence 7.5 Minute U.S.G.S. quadrangle in Van Buren County, in southwest Michigan suggest lithologies and landforms consistent with ice advance. The Lake Michigan Lobe of the Laurentide Ice sheet most recently modified the study area. The drift thickness in the area ranges from 150-400 feet and overlies the Mississippian Coldwater shale of the Michigan Basin. Subsurface data was gathered by hand augering, mud rotary drilling with split-spoon samples, continuous core rotosonic drilling, natural gamma radiation logs and county water well records. Bedrock topography and drift thickness maps were constructed using oil well data. The study area is centered over the Valparasio Morainic system. The relief of the area is moderately high. The Paw Paw River valley incises the northern portion of the map. This valley has been interpreted as an outlet for a glacial lake to the east and may have even been created catastrophically. Most of the uplands in the area are capped with a clay-rich, reddish-brown diamicton that contains numerous cobbles and small boulders. Underlying this surface diamicton are outwash and lacustrine sediments. The areas lower in elevation are composed of sand, silt, and in some areas, clay, which may represent a reworking of surface sediments as demonstrated by the variable flow directions. These sediment assemblages suggest glaciofluvial or glaciolacustrian origins. The central portion of the map is dominated by a moderately high area that consists of very fine to medium sand. A stream flowing through this area is deeply entrenched which suggest a rapid change in base level. This change in base level was most likely caused by a change in level of the lake or river that was occupying the Paw Paw River valley. Some upland areas are covered by thin cap of fine sand but are underlain by diamicton. This sequence has been interpreted as eolian sand.