A multi-proxy palaeoecological and palaeoclimatic record within full glacial lacustrine deposits, western Tennessee, USA
David A. Grimley, Daniel Larsen,
Samantha W. Kaplan, Catherine H. Yansa, B. Brandon Curry, and Eric A. Oches
The Fulton Section, along the Mississippi River in western Tennessee, USA, is a 1 km continuous exposure (20m vertically) of Quaternary fluvial and lacustrine deposits, inset within Eocene sediments and buried by thick loess. Fossiliferous slackwater lake sediments record maximum aggradation during the last two major glaciations, with deposition between ca. 190–140 ka andQ1 24– 18 14C ka BP, based on amino acid and radiocarbon chronology, respectively. During the onset of full glacial conditions (ca. 24–22 14C ka BP), a relatively permanent shallow lake environment is indicated by ostracodes, aquatic molluscs, and both pollen and macrofossils of aquatic plants. By 21.8 14C ka BP, increasing emergent plants, amphibious gastropods (Pomatiopsis) and heavier d18O compositions suggest marsh-like conditions in a periodically drying lake. The surrounding uplands consisted of Picea–Pinus woodlands mixed with cool-temperate hardwoods (e.g. Quercus, Populus, Carya), grasses and herbs. More open conditions ensued ca. 20 14C ka BP, with loess and slopewash gradually infilling the former lake by 18 14C ka BP. Modern analogue analyses of ostracodes and palaeontological evidence imply a full glacial climate similar to today’s mixed-boreal zone in central Minnesota, USA, about 98C cooler in mean annual temperature than present-day western Tennessee.