POLYGONAL CRACKING ON LATE PLEISTOCENE TERRACES WITHIN THE TENNESSEE RIVER VALLEY, A STRATIGRAPHIC MARKER HORIZON AND ITS POTENTIAL PALEOCLIMATIC SIGNIFICANCE
The buried polygonal cracks extend vertically 1 m in profile and taper to a point at the base. The polygons are up to 50 cm in diameter and the top of some cracks appear to be wedge-shaped. The polygons occur on the elevated Holocene T2 terraces. These treads are interpreted as the Late Pleistocene T1 terraces, prior to incision of the Tennessee River into its present channel. Preservation across this surface varies because of root bioturbation. Terrace sediment is a fine sandy, silt (51-68% fines) and clay mineralogy is dominated by chlorite, vermiculite, illite and montmorillonite. There is little difference in the particle size distribution between the alluvium and crack fillings.
One of the principal roles of a geomorphologist is to determine how deep archaeologists need to test in order to reach culturally sterile deposits. These Late Pleistocene features form an important marker horizon as they pre-date (16ka BP) documented Native American occupation within the SE United States. Further work is underway to interpret formation processes to provide a paleoclimatic proxy for conditions within the Tennessee River Valley during the LGM.