MAPPING OF STREAM TERRACE ALLUVIAL DEPOSITS NEAR TUPELO, MISSISSIPPI (Invited Presentation)

Surface geologic mapping along the Natchez Trace Parkway and National Scenic Trail resulted in identification of several levels of stream terrace alluvial deposits in the Guntown, Sherman and Bissell 7.5 minute quadrangles near Tupelo, MS. The mapping was conducted as part of the National Park Service’s delineation of geologic resources. Surficial units mapped on these quadrangles were Cretaceous sediments with Quaternary alluvium and terrace deposits. There were different levels of terrace deposits identified that had previously been mapped as a Cretaceous chalk formation. In many areas five different levels of terrace alluvium deposits were identified.

In many areas the terrace deposits had been previously mapped at a county wide level during the mid-1900s as a Cretaceous chalk, the Demopolis Formation. During the current mapping effort several locations were identified that have upper level stream terrace deposits incised into the underlying chalk. In some instances a lower terrace deposit had been deposited below the base of the higher terrace deposit resulting in the chalk being exposed at the base of the upper terrace deposit. The upper terrace deposits are more eroded than the lower ones, and resemble the gently rolling terrain of the Cretaceous Demopolis Formation chalk. There is significant soil cover and vegetation in the area which combined with gently rolling terrain, results in very few good exposures of the geologic units. It appears that the occasional chalk exposure combined with the similar gently rolling topography led early mappers to believe many of the areas with higher level terrace deposits were areas of Cretaceous Demopolis Formation chalk. This seems to be most often associated with the stream terrace deposits above the lower two terraces.

Mapping of the stream terrace deposits and differentiating between the different levels of terraces allowed for the determination of several levels of terraces, some of which had been previously mapped as a Cretaceous chalk formation. Had the different levels of terraces not been determined, the areas of gently rolling terrain that are eroded Quaternary terrace deposits rather than Cretaceous Demopolis Formation chalk might not have been discovered.