Last glacial maximum ecology and climate from terrestrial gastropod assemblages in Peoria loess,western Kentucky |
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| Authors: | David A Grimley Ronald C Counts Jessica L Conroy Hong Wang Sarah N Dendy Catherine B Nield |
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| Institution: | 1. Illinois State Geological Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, USA;2. Mississippi Mineral Resources Institute, Department of Geology and Geological Engineering, University of Mississippi, USA;3. Department of Geology, University of Illinois at Urbana-Champaign, USA
Department of Plant Biology, University of Illinois at Urbana-Champaign, USA;4. Beijing Normal University, Beijing, China;5. Department of Geology, University of Illinois at Urbana-Champaign, USA |
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| Abstract: | The Rocks loess section, in unglaciated western Kentucky, provides a high-resolution environmental record during the last glacial maximum onset. The Peoria Silt (9 m thick) contains 26 terrestrial gastropod species, with up to 15 species within a single 5 cm interval. Thirteen radiocarbon ages, using shells or charcoal, range between 30 and 24.5 cal ka; younger loess has been leached or eroded. Stratigraphic shifts in gastropod assemblages imply significant cooling, particularly ~27 cal ka, as solar insolation was decreasing and the southern Laurentide Ice Sheet rapidly advancing. Midwestern to southern species (e.g. Anguispira kochi, Gastrocopta pentodon, Hawaii miniscula, Helicodiscus parallelus, Vallonia perspectiva) occur only in the lowermost Peoria Silt (~30–27 cal ka). In contrast, cold-tolerant species (Columella alticola, Vertigo modesta, Vallonia gracilicosta) occur only in full glacial Peoria Silt (27–24.5 cal ka). Inferred mean July temperatures, from mutual climatic range methods, range from ~23 °C at 30 cal ka, cooling to ~18 °C by 26 cal ka; about 3–8 °C cooler than today (~26 °C). Superimposed on this cooling trend are multi-centennial variations in detrital carbonate, fossil shell concentrations, palaeotemperature estimates, and oxygen isotope values (Vertigo, Discus, Helicodiscus). The finer-scale variations imply relatively synchronous fluctuations in glacial sediment supply, loess sedimentation, and climate. |
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| Keywords: | Kentucky last glacial loess stable oxygen and carbon isotopes terrestrial gastropods |
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