USING A TOPOGRAPHIC RESIDUAL ENVELOPE MAP AS A RAPID IDENTIFICATION TECHNIQUE FOR TECTONIC DEFORMATION WITHIN QUATERNARY TERRACES OF THE SALINE RIVER FAULT ZONE IN SOUTH-CENTRAL ARKANSAS

Within the past twenty years, research within the Saline River fault zone (SRFZ) (strike = 135°) in the southern Mississippi Embayment has outlined a regional zone of Quaternary paleo-seismicity that trends along the southern passive margin of the North American Craton, marked by the Oklahoma-Alabama Transform Zone. Faults within this zone offset Pleistocene to Holocene alluvial terraces overlying Eocene marine sediments. These terraces consist of the middle Pleistocene-aged Intermediate Complex terraces, the Sangamon-aged Prairie Complex terraces, the Wisconsin-aged Deweyville Complex terraces, and the active and abandoned Holocene terraces.

These terraces are remnants of former floodplains along the Tertiary Upland divides of the Ouachita and Saline River Valleys in southeastern Arkansas. The original geometry of these terraces has been dissected by erosion and may have been tectonically deformed. In order to understand the extent of deformation of these terraces erosion must be subtracted from a digital elevation model.

After extraction of tributary divides that cross the terraces of the Saline and Ouachita River Valleys, a continuous terrain that extrapolates between the tributary divides was constructed, and the lateral and horizontal boundaries of these terraces were defined. This method is designed to delete erosion from the terraces to permit the extent of deformation within each of these terraces to be assessed by measuring the deviation between their modelled geometry on this envelope map and the active flood plains. Preliminary results show that the Intermediate Complex terrace level has a pronounced convexity consistent with tectonic deformation.