DENUDATION OF THE PLIOCENE-PLEISTOCENE UPLAND GRAVEL IN THE UPPER MISSISSIPPI EMBAYMENT AND ITS STRUCTURAL IMPLICATIONS

The original extent of the Pliocene-Pleistocene Upland Gravel (Lafayette Gravel) of the Upper Mississippi Embayment remains enigmatic. We believe that the Upland gravel used to extend across the Mississippi River valley eastern lowlands from western Tennessee and Kentucky to Crowley's Ridge in Missouri and Arkansas. Based on this interpretation we analyzed the denudational history of the Upland Gravel from the eastern lowlands during the Quaternary and its influence on the New Madrid seismic zone.

Over 8000, 300 foot deep geologic well logs in Tennessee, Arkansas, Missouri, and Kentucky were interpreted to record the elevation of the top and bottom of the gravel facies within the Upland Gravel. These elevations were used to create structure contour maps, isopachous maps, trend surface maps, and cross sections of the gravel. A DEM surface map was subsequently subtracted from the gravel surface map to determine the thickness of sediment removed during the Quaternary from the eastern lowlands, which includes the New Madrid seismic zone.

Our maps illustrate an interpolated surface of the top of the Upland Gravel from the Mississippi River bluff line in western Kentucky and Tennessee to Crowley's Ridge in Arkansas and Missouri. Previous research on seismicity in Greenland and Antarctica has proposed that the vertical stress imposed by continental ice sheets is capable of stabilizing reverse faults and Holocene ice ablation in Fennoscandia has caused recent reverse faulting. Thickness calculations of the sediment removed from the eastern lowlands are examined to evaluate if Quaternary denudation could have stimulated Holocene reverse faulting within the New Madrid seismic zone.