QUATERNARY PALEOECOLOGY OF THE LOWER MISSISSIPPI VALLEY

In 1938, Clair A. Brown published his classic paleobotanical discoveri es from the Tunica Hills of southeastern Louisiana, indicating ice-age plant migrations of more than 1100 km. Brown collected fossils of bot h boreal trees such as white spruce (Picea glauca) and southern coasta l plain plants from deposits mapped as the Port Hickey (Prairie) river terrace by Harold N. Fisk. Subsequent revisions of terrace mapping, r adiocarbon dating, and paleoecological analysis reconciled Brown's con ceptual and stratigraphic ''mixing'' of these two ecologically incompa tible fossil plant groups. An older Terrace 2 (of Sangamonian to Alton ian age) contains the warm-temperate assemblage. A younger Terrace I ( of Farmdalian, Woodfordian, and Holocene age) includes full-glacial an d late-glacial remains of both boreal and cool-temperate plants; and a warm-temperate suite of plants dates from the Holocene interglacial. New plant fossil localities with radiocarbon chronologies are now avai lable from within the Lower Mississippi Valley of Missouri and Arkansa s as well as from the adjacent Ozark Plateaus, the Interior Low Platea us of Kentucky and Tennessee, and the bordering Blufflands of Tennesse e, Mississippi, and Louisiana. These studies demonstrate that glacial and interglacial patterns of vegetation have been influenced by region al changes in climate, glacial runoff, and regime of the Mississippi R iver.