SEDIMENT LOAD AND PALEOCLIMATE CONTROL ON LATE PLEISTOCENE FLUVIAL-TERRACE DEVELOPMENT IN WESTERN TENNESSEE

The late Pleistocene Hatchie and Finley fluvial terraces are situated along tributaries to the Mississippi-Ohio River system in western Tennessee. These terraces precede the glacial maxima of the late Pleistocene Laurentide ice sheet, as well as the subsequent Prairie and OIS 2 terrace systems along the eastern lowlands of the Mississippi River valley (MRV). Radiocarbon dating of valley-fill and marsh deposits within the Finley terrace deposits indicates an age range of ~28,000 – 21,000 calendar years before present (cybp). Conversely, radiocarbon and optically stimulated luminescence (OSL) dating of MRV alluvium from core from the eastern lowlands yields dates as old as ~17,000 cybp, suggesting that MRV alluvium aggraded as much as 4,000 years after the Finley terrace. Similar comparisons can be made for the Hatchie terrace in relation to the Prairie complex terraces, albeit with less precise age control.

Current data do not support base level or tributary channel length as the primary control for Finley or Hatchie terrace aggradation. Quaternary tectonics in western Tennessee are found to influence the development of the Finley and Hatchie terraces, though not their timing. The late Pleistocene MRV terrace systems in the eastern lowlands display complex correlations to glacial dynamics and sea level during and following peak-glacial conditions. In contrast, the western Tennessee terraces correlate with incipient loess deposition and paleoclimate deterioration prior to peak OIS 6 and 2 glaciations. Paleobotanical and other paleoclimate data indicate significantly drier and cooler conditions than the present or immediate post-glacial maxima in the MRV.

The conditions conducive to aggradation along western Tennessee tributaries are attributed to sediment loading from incipient MRV deflation of aeolian silt and cooler, drier climate conditions, especially in northwestern Tennessee. Notably, Finley and Hatchie terrace development is less prominent along tributaries in southwestern Tennessee. The base-level fall along the MRV immediately prior to peak glaciation may have arrested aggradation and initiated terrace development in western Tennessee. This investigation emphasizes the need for caution when correlating terraces in the MRV region and highlights the importance of considering upstream controls alongside glacial and base-level drivers.