EVIDENCE FOR NEOTECTONISM IN NORTHERN MISSISSIPPI FROM DRAINAGE BASIN ASYMMETRY

Analysis of traverse topographical asymmetry of drainage basins (T index) defines several geomorphic domains in coastal plain sediments of northern Mississippi (33º to 35º N, 88.5º to 90.5º W) that may reflect a system of deep crustal blocks bounded by active faults or flexures. T index data, a measure of long-term lateral stream migration, are displayed as a 2-D vector field.

We measured this morphometric index for all second order drainage basins (following Strahler, 1952) and produced a statistically significant vector field, from which we defined 12 domains. A principal domain boundary divides the study area in a NE-SW direction, and outcrop lineaments and earthquakes epicenters correspond to this boundary (including a MW 6.1 aftershock of the 1811 New Madrid earthquake sequence). Our preliminary survey of Holocene alluvium reveals possible sand blows along the southwestern part of this boundary. Results from other morphometric techniques (longitudinal and topographic profiles, ruggedness analysis, etc…) we applied are in accord with the active crustal blocks defined by basin asymmetry analysis. Drainage patterns and local differences in incision level suggest headwaters capture has been more pronounced along some prominent T index domain boundaries, and thus capture may be related to tectonic movements.

There are two Paleozoic fault systems in our study area, the NE-striking Mississippi Valley graben and the NW-striking Ouachita thrust belt and foreland fault zone. Several of our domain boundaries correspond to mapped faults of these systems (e.g., the White River fault zone), but some prominent boundaries seem to reflect previously unmapped faults (flexures?) parallel to the strikes of these systems. Results of our satellite image lineament analysis of a sub-region in the NE study area are in accord with subsurface structural grains and our domain boundaries.