INVESTIGATING POTENTIAL NEOTECTONIC DEFORMATION WITHIN WEST-CENTRAL MISSISSIPPI USING DRAINAGE-BASIN ASYMMETRY IN THE BIG BLACK RIVER SYSTEM

Potential neotectonic activity within the Big Black River (BBR) system near Edwards, Mississippi was investigated using 7.5 minute USGS topographic quadrangles and rapid quantitative techniques. A 40 km reach of the BBR WNW of Edwards, MS exhibits morphometric characteristics that are different than upstream and downstream reaches. The BBR appears shifted laterally within its alluvial valley and an anomalous ~6.5 km straight segment of the river is located at the BBR and Interstate 20 intersection. The entire study area (~130 km reach of the BBR) was divided into three sub-reaches defined by alluvial valley and active floodplain width, sinuosity, and slope. The upper and lower reaches within the study area have similar sinuosity as the entire BBR (1.75), while the middle reach’s sinuosity drops below the 1.5 meandering threshold and is a straight channel. Channel and valley slopes and sinuosity were also measured in the tributaries flowing into the three sub-reaches of the BBR. The average tributary channel and valley slopes within the middle reach (0.006052 and 0.007189 respectively) are nearly double the slopes of the upper and lower reaches tributaries. Lateral stream migrations within the tributaries were quantitatively analyzed by measuring the asymmetry factor (AF) and transverse topographic symmetry factor (T) indices. Both techniques suggest minimal lateral shifting (AF: 44.2-upper, 56.8-middle, 53.0-lower; T: 0.314-upper, 0.282-middle, 0.329-lower) of tributary stream channels in all three sub-reaches. The small tributaries measured in this study may reflect a more localized control on morphometry and might not reveal deformation caused by tectonic activity.