GEOMORPHIC EVIDENCE FOR THE STRUCTURE AND TIMING OF THE NORTH LOUISIANA TECTONIC ZONE

Northern Louisiana is marked by significantly greater topography than surrounding areas. Initial tectonic analysis shows a broad regional uplift (of which the Monroe uplift is the eastern part) with a series of parallel localized linear uplifts that are deforming river valleys, creating significant escarpments with asymmetric drainage patterns, and creating a fracture dominated drainage pattern. When viewed in a regional context, these uplifts appear to form two active, oblique, thrust systems; this suggestion is supported by subsurface data. The east-striking (085-095) set of thrust surfaces is doubly verging (north on the north side and south on the south side) forming regional antiformal uplift that forms the core of the Louisiana hill country. Rivers are deeply incised along successive steep-sided linear valley segments (following fractures apparently associated with both deformational systems) across the broad uplift, and localized uplifts above thrust ramps have created several lakes during the Holocene, some of which are still extant despite the poor consolidation of the uplifted strata. The northeast-striking (030-040) set of thrust faults is generally southeast verging and create the escarpments along the western boundaries of the Mississippi floodplain. These escarpments are geomorphically very immature with drainage divides generally occurring immediately adjacent to the crests of the escarpments. The geomorphic evidence for both thrusts systems indicate that the faulting is active and that the uplift rates are high.