Middle to Late Pleistocene loess record in eastern Nebraska,USA, and implications for the unique nature of Oxygen Isotope Stage 2 |
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| Institution: | 1. Polar Research Center, Jilin University, No. 938 Ximinzhu Str., Changchun City 130061, China;2. College of Construction Engineering, Jilin University, No. 938 Ximinzhu Str., Changchun City 130061, China;1. Iowa Department of Natural Resources, 900 East Grand, Des Moines, IA, USA;2. Iowa Geological and Water Survey, 109 Trowbridge Hall, Iowa City, IA 319-335-1575, USA;3. Department of Natural Resource Ecology and Management, Iowa State University, Ames IA, USA;4. National Laboratory for Agriculture and Environment, Agricultural Research Service, United States Department of Agriculture, Ames, IA, USA;1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an 710061, China;2. Joint Center for Global Change Studies, Beijing 100875, China;3. State Key Laboratory Breeding Base of Humid Subtropical Mountain Ecology, School of Geographical Sciences, Fujian Normal University, Fuzhou 350007, China;4. Research Center for Ecology and Environment of Center Asia, Chinese Academy of Sciences, Urumqi 830011, China;5. Institute of Geology, Earthquake Engineering and Seismology, Academy of Sciences of Tajikistan, Dushanbe 734063, Tajikistan |
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| Abstract: | New subsurface data reveal a nearly continuous stratigraphic record of Middle to Late Pleistocene loess sedimentation preserved beneath upland summits in eastern Nebraska, USA. Thickness and grain size trends, as well as pedologic evidence, indicate significant changes in loess sources, accumulation rates, and depositional environments. The newly defined Kennard Formation accumulated in the Middle Pleistocene, and may represent multiple thin increments of distal loess from nonglacial sources on the Great Plains. The overlying Loveland Loess, up to 18 m thick and deposited during Oxygen Isotope Stage 6 (OIS 6) (Illinoian glaciation), probably records the emergence of the Missouri River valley as a major glaciogenic loess source. The prominent Sangamon Geosol formed through long-term pedogenic alteration of the upper Loveland Loess during OIS 5 and 4. Thin loess of the Gilman Canyon Formation records slow loess accumulation and pedogenic alteration in OIS 3. The Peoria Loess (OIS 2) is similar in thickness to Loveland Loess, but may have accumulated more rapidly in an environment less favorable to bioturbation. More importantly, comparison of Peoria and Loveland loess thickness trends indicates much greater influx of nonglaciogenic loess from the Great Plains during OIS 2 than in OIS 6, suggesting colder and/or drier conditions in the Midcontinent during OIS 2 than in earlier glacial stages. |
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