MAPPING HIGH-TERRACE DEPOSITS IN KARST TERRAIN, EAST-CENTRAL TENNESSEE

Mapping the surficial geology at 1:24,000 scale in the Cookeville East quadrangle was performed to characterize these deposits and understand their origin. Eleven units were mapped based upon geomorphology and texture of the regolith. Bedrock in the area is mainly cherty and non-cherty Mississippian limestone with some siliciclastic units. Mapping in karst presents difficulties caused by the antiquity of most of the deposits. Internal drainage, which is prevalent in karst regions, helps preserve surficial deposits that otherwise would be eroded by streams. Thus, many of the surficial deposits attain great age and display intense weathering. Landscapes are lowered by solution rather than stream erosion, and originally flat surfaces, such as terraces and floodplains, are lowered irregularly rather than being dissected. The regolith in the map area, which generally is several meters thick, has a red Munsell hue of 5YR or 2.5YR and is rich in clay. Of particular interest are the upland deposits that form terrace-like features. The Putman County Soil Survey states that much of the highly weathered transported regolith is underlain by a clay-rich residuum derived from the bedrock. Distinguishing transported regolith from residuum is difficult when fluvial surfaces cannot be recognized. In the Cookeville area, transported material can be identified by the presence of rounded quartz pebbles that eroded from the Pennsylvanian conglomerates on the Cumberland Plateau to the east. Residuum is recognized in the map area by the presence of angular chert fragments, many of which are so weathered they can be crushed with the hand. Augering into these deposits often reveals neither quartz pebbles nor angular chert, and one is uncertain if the deposits are transported or residual. However, based on the geomorphology of the upland deposits, their proximity to modern streams, and the presence of rounded quartz pebbles, we conclude that the high terraces of the Cookeville East quadrangle represent ancient floodplains.