At the Bon Harbor Hills Section in western Kentucky, approximately 11 m of last glacial loess deposits (predominantly Peoria Silt) are found, perhaps the thickest loess observed in the lower Ohio River valley region. The late Wisconsin Episode loess sequence consists of at least 9 loess-paleosol couplets, consisting of weakly developed incipient paleosols. The middle Wisconsin Episode Roxana Silt is about 0.5 - 1 m thick, but is not readily recognizable, and overlies a full interglacial Sangamon Geosol developed in Illinois Episode loess (Loveland Silt). Luminescence and radiocarbon ages bracket the last glacial loess to between about 25 k and 11 k cal yr BP. Magnetic susceptibility in the Peoria Silt generally ranges between 40 and 80 X 10 (super -8) m (super 3) /kg, with highest values tending to occur in more rapidly deposited zones with coarser silt. Total carbonate percentages alternate from 20 - 40 % in least altered, rapidly deposited Peoria loess to 5 - 10 % in the more darkly colored weak paleosols, suggesting climatic conditions and stable landscapes conducive to carbonate dissolution. Fossil terrestrial gastropods (1 - 10 mm in size) are dispersed throughout the calcareous loess, but are less abundant or absent in partially leached incipient paleosols. Common gastropods in the Peoria Silt include Vallonia gracilicosta, Vertigo modesta (common to northern boreal forests), Punctum minutissimum, Discus whitneyi and Hendersonia occulta. The largest species, Anguispira alternata, is found only in the basal zone at 9 - 10 m depth below ground surface, and probably indicates a less severe climate. Succinea avara is present only in the upper 5 m of loess, immediately above a zone of coarser silt, perhaps suggesting its introduction from the west (Wabash Valley ?) during a severe windstorm or a change in environmental conditions. Columella alticola, suggestive of peak cold conditions during last glaciation, occurs only in samples at 5.45 and 6.15 m ( approximately 17.5-19 k cal yr BP). Euconolus fulvus is found only in samples at 3.45 and 3.75 m. Several gastropod eggs of 1 mm diameter (probably of Succinea sp.) and juveniles of Discus whitneyi were also found in the 3.75 m sample. The combination of compositional and paleontological indicators show potential use for differentiation of stratigraphic zones, as well as for identifying paleoenvironmental and paleoclimatic changes.
|Original language||English (US)|
|Title of host publication||Abstracts with Programs - Geological Society of America|
|Publisher||Geological Society of America (GSA), Boulder, CO, United States (USA)|
|State||Published - 2008|