GLACIAL AND POSTGLACIAL GEOMORPHOLOGY OF TIPPECANOE COUNTY, INDIANA

We used LiDAR topography to map glacial and periglacial features in Tippecanoe County, Indiana, near the southern margin of the Laurentide Ice Sheet. The map reveals a palimpsest of landforms associated with ice advance and retreat. We describe some of these here in chronological order:

The area was last glaciated by the East White sublobe, which advanced over older Michigan Lobe till. Radiocarbon dating of a log recovered locally shows that Late Wisconsin ice advanced here at 22,500 +/- 500 radiocarbon years BP (West and Granger, 2018, Indiana Acad. Sci.). The topography is dominated by a NE-SW drainage pattern that follows subglacial tunnel valleys and eskers, and by a subperpendicular set of recessional moraines. A number of features are associated with deglaciation and ice collapse, including rectilinear kames that likely formed in fractured ice; a meandering supraglacial stream channel that cut into the underlying till; and numerous kettle holes. After deglaciation the area was subject to permafrost conditions, as evidenced by widespread thaw lakes and ice-wedge polygons. The county is bisected by the Wabash River, which follows a channel occupied by at least two cataclysmic floods. The older flood likely occurred near the ice margin (Fraser and Bleuer, 1988, GSA Spec. Pap. 229). The younger flood is the Maumee Torrent, released by the collapse of the Fort Wayne moraine near 14,000 radiocarbon years BP (Fullerton, 1980, USGS PP 1089). Cataclysmic flood deposits are distinguished by streamlined bedforms, cross-bar channels, kettles in bar deposits, and megaripple trains. Periglacial features are generally present on the older flood features, but absent on terraces of the Maumee torrent. Finally, the youngest features include parabolic dunes and dune fields formed by westerly winds.