The Last Glacial Maximum (LGM)

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The Last Glacial Maximum (LGM) What is the LGM? The last glacial maximum (LGM) is the term used for the most recent period in which the major ice sheets reached their maximum volume. Evidence from palaeo (past) climate records, such as deep ocean sediments, fossils, and glacial landforms, shows that this occurred at around 21,000 years ago (21 ka). Due to spatial variations in air temperature change, and because large ice sheets sometimes take a long time to respond to such changes, the LGM actually spans a time period from around 26- 19 ka. What were conditions like in the LGM? During the LGM, average air temperatures across the globe were 2-6°C cooler than the present day. The Greenland and Antarctic ice sheets were much larger, and extended onto the continental shelf. In addition, ice sheets developed across vast areas of Eurasia and North America. In Britain, a large ice sheet, the British-Irish Ice Sheet, extended from the mountains of Scotland, and across Cheshire (Fig. 1). Ice caps and mountain glaciers, which are much smaller than the ice sheets, also developed on many high mountains; some of these have survived to the present day, such as in the Alps and the Himalaya. These ice masses carved the landscapes that we see around us today. Because large volumes of water became locked up in the major ice sheets and glaciers, global sea level fell by around 135 m (Fig. 2). At the end of the LGM, glaciers retreated - many of them disappeared entirely - and sea level began to rise towards its present day, Holocene, position. Figure 1 – The extent of ice masses (shown in blue) in the northern hemisphere during the Last Glacial Maximum (LGM). Source: http://www.qpg.geog.cam.ac.uk/lgmextent.html Figure 2 – Schematic diagram of sea level change over the last 200,000 years, showing the Last Glacial Maximum (LGM) in comparison to the Holocene and previous glacial and interglacial periods. (Source: http://www.eeescience.utoledo.edu/Faculty/Krantz/Va_Coast_figures/Virginia_Coast_figures.htm) .

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Wisconsinan and Sangamonian Type Sections of Central Illinois
557 IL6gu Buidebook 21 COPY no. 21 OFFICE Wisconsinan and Sangamonian type sections of central Illinois E. Donald McKay Ninth Biennial Meeting, American Quaternary Association University of Illinois at Urbana-Champaign, May 31 -June 6, 1986 Sponsored by the Illinois State Geological and Water Surveys, the Illinois State Museum, and the University of Illinois Departments of Geology, Geography, and Anthropology Wisconsinan and Sangamonian type sections of central Illinois Leaders E. Donald McKay Illinois State Geological Survey, Champaign, Illinois Alan D. Ham Dickson Mounds Museum, Lewistown, Illinois Contributors Leon R. Follmer Illinois State Geological Survey, Champaign, Illinois Francis F. King James E. King Illinois State Museum, Springfield, Illinois Alan V. Morgan Anne Morgan University of Waterloo, Waterloo, Ontario, Canada American Quaternary Association Ninth Biennial Meeting, May 31 -June 6, 1986 Urbana-Champaign, Illinois ISGS Guidebook 21 Reprinted 1990 ILLINOIS STATE GEOLOGICAL SURVEY Morris W Leighton, Chief 615 East Peabody Drive Champaign, Illinois 61820 Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/wisconsinansanga21mcka Contents Introduction 1 Stopl The Farm Creek Section: A Notable Pleistocene Section 7 E. Donald McKay and Leon R. Follmer Stop 2 The Dickson Mounds Museum 25 Alan D. Ham Stop 3 Athens Quarry Sections: Type Locality of the Sangamon Soil 27 Leon R. Follmer, E. Donald McKay, James E. King and Francis B. King References 41 Appendix 1. Comparison of the Complete Soil Profile and a Weathering Profile 45 in a Rock (from Follmer, 1984) Appendix 2. A Preliminary Note on Fossil Insect Faunas from Central Illinois 46 Alan V.
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