GLACIAL MAPPING AND SUBSURFACE EXPLORATION OF THE GLENN, LACOTA, AND SOUTH HAVEN U.S.G.S 7.5 MINUTE QUADRANGLES OF ALLEGAN COUNTY, MICHIGAN

Results of a recently completed STATEMAP project for the Glenn, Lacota, and South Haven 7.5 Minute U.S.G.S. quadrangles in Allegan County, southwestern Michigan, suggest lithologies and landforms consistent with an ice advance. The Lake Michigan Lobe of the Laurentide Ice sheet deposited glacial drift ranging from 15-153 meters thick overlying the Mississippian Coldwater Shale. Subsurface data was gathered by hand augering, 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 contains the Lake Border Morainal System which lies subparallel to the shoreline of Lake Michigan in southwest Allegan County. A rolling upland surface of moderate relief parallels the shoreline and encompasses the northern regions of the study area. These areas are capped with a clay-rich, reddish-brown diamicton. Underlying this surface diamicton are bedded sand-to-silt-to-clays of lacustrine origin. Some upland areas are covered by a thin cap of fine eolian sand that is underlain by diamicton. The central and southwestern regions of the study area are composed mainly of a broad gently sloping plain of low relief. These areas are composed of bedded sands and gravels with areas of bedded silts and clays. These sediment assemblages, which are capped in places with eolian sand, are of glaciofluvial or glaciolacustrian origin. Within the central region of the study area lies an area of moderate relief containing topography similar to the Lake Border Morainal System along the western edge of the study area. Previous research in this area has included these landforms as part of the Lake Border Morainal System. However, this study has shown that the stratigraphy of the upland area of moderate relief is composed of thick beds of lacustrine sand and silt, with no diamicton unit similar to the one that caps the moraine.