DISTRIBUTION AND POSSIBLE FAULT DISPLACEMENT OF THE UPLAND GRAVEL OF WESTERN TENNESSEE

Approximately 10,000 lignite exploration wells have been drilled and logged in western Tennessee by the Phillips Coal Company. The wells have been drilled on a one to two mile grid to a depth of 300 feet as part of a lignite exploration program. In these well logs we have picked the top and bottom of the gravel portion of the Pliocene-Pleistocene Upland Gravel (Lafayette Gravel). The Upland Gravel is a fluvial sand and gravel deposit that underlies the loess of western Tennessee. The top of the gravel section is delineated in the logs by the first appearance of the gravel in the well and the base of the gravel is delineated by the deepest recorded gravel. Ground surface elevation of the well, top and bottom elevations of the gravel, and thickness of the gravel were recorded.

The distribution of the gravel portion of the Upland Gravel was mapped in the westernmost Tennessee counties of Obion, Weakley, Henry, Dyer, Gibson, Carroll, Lauderdale, Crockett, Tipton, Haywood, Madison, Henderson, Shelby, Fayette, Hardeman, Chester, and McNairy. Structure contour maps of the top and bottom of the gravel, an isopachous map, and cross sections of the gravel were made. These maps and cross sections support the interpretation that the Upland Gravel is a terrace of the south flowing ancestral Mississippi/Ohio River and provide a general picture of the distribution and thickness of this gravel (aggregate) resource. The structure contour maps also suggest Quaternary faulting and thus potentially seismogenic faults in western Tennessee.