Nature and origin of corrugated ground moraine of the Des Moines lobe,Story County,Iowa |
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| Institution: | 1. Key Laboratory of Agricultural Ecology and Environment, Shandong Agricultural University, Taian 271018, China;2. College of Forestry, Agricultural University of Hebei, Baoding 071000, China;3. Shandong Forest Tree Seedling Station, Jinan 250014, China;4. Institute of Agro-biotechnology, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China;5. Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China;1. Stearns, Conrad & Schmidt, Consulting Engineers, Inc., Yukon, OK 73099, USA;2. Department of Integrative Biology, Oklahoma State University, Stillwater, OK 74078, USA;1. Department of Biology, East Carolina University, Greenville, NC, USA;2. Aquatic Ecosystems Program, IRTA, St. Carles de la Ràpita, Catalonia, Spain;3. US National Park Service, 200 Chestnut Street, Philadelphia, PA 19106, USA;1. Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, China;2. College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;3. Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark;4. Dongting Lake Station for Wetland Ecosystem Research, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China;1. Facultad de Ciencias Naturales, Universidad Autónoma de Querétaro, Querétaro, Mexico;2. Instituto de Ecología, A.C. Red de Diversidad Biológica del Occidente Mexicano, Centro Regional del Bajío, Pátzcuaro, Mexico;3. CONACyT, Ciudad de México, Mexico;4. Laboratorio de Sistemática Vegetal Molecular, Universidad de Guadalajara, Zapopan, Jalisco, Mexico |
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| Abstract: | Corrugated ground moraine in Story County, Iowa consists of low relief (1–2 m) ridges which most commonly consist of late Wisconsinan till. The average spacing between ridges is about 105 m, and they generally parallel the configuration of the Bemis Moraine, the terminal moraine of the Des Moines glacial lobe. Till fabric (pebble orientations and anisotropy of magnetic susceptibility), facies variations and landform fabric analyzed at three sites in typical corrugated ground moraine landscape near Ames in Story County, Iowa indicate that at sites 1 and 2 the ridges consist of till probably deposited by lodgement. At site 3, two ridges consist of till and massive to cross-bedded sand. Till at site 3 is also probably lodgement till. The nature of the till and related glaciofluvial sediments at each site suggests that the corrugation ridges formed in basal cracks or crevasses in the Des Moines Lobe. The cracks are postulated to have formed during extending flow of the Des Moines lobe as it advanced toward its terminal position. Retreat of the Des Moines lobe was rapid enough to preclude significant accumulations of supraglacial sediment upon corrugated ground moraine. |
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