GEOGRAPHIC DISTRIBUTION OF OLD, HIGH-LEVEL ALLUVIAL DEPOSITS IN EAST-CENTRAL TENNESSEE AND IMPLICATIONS FOR ORIGIN

Previous study of surficial deposits in the Cookeville East quadrangle and nearby areas showed widespread distribution of transported regolith that appears to be at least partly alluvial in nature. Field and lab studies, including particle-size and X-ray diffraction, show most of the deposits to be intensely weathered and presumably quite old. Deposit thickness is usually only several meters, the deposits typically being underlain by residuum and bedrock. The purpose of the present study is to look at the larger picture, the variation of these deposits over a large area of east-central Tennessee, and to attempt to determine how closely their distribution is controlled by topography (including paleo-topography) as opposed to control by the underlying bedrock. Methods include the use of DEMs and digital versions of the Tennessee State geologic map and soil map. The soil map was used to describe the distribution of old alluvial deposits by using soil series such as the Waynesboro as proxies for the deposits. Draping maps of alluvial deposits over topographic maps of the study area allows the manner in which topography controls alluvial deposits to be determined. Superimposing alluvial deposit maps on the geologic maps allows the control of rock types on the distribution of alluvial deposits to be determined. These methods showed, as expected, that the locations of many alluvial deposits are controlled by underlying bedrock, but that in other cases deposits are in equilibrium with the present topography, such as being located on the footslopes of the Cumberland Plateau escarpment. We hypothesize that the deposits have formed from streams eroding the margins of the Plateaus and then depositing the eroded sediments onto the escarpment piedmont.