ABSTRACT

The North Louisiana basin is an interior basin in the northern part of the Gulf of Mexico margin that formed by rifting during the Jurassic. Evaporites, transgressive carbonates, and continental to deltaic sediments accumulated after the rift phase. The basin infilling was not continuous in time, and the region was also influenced by two major and some minor relative sea-level changes that can be attributed to tectonic and/or eustatic events. The increasing thickness of sediments deposited on the basement led to flexural deformation.

The investigation reported here considers flexural modeling of the north Louisiana region during the post-rift phase. Pure elastic, plastic-elastic, and thermo-elastic models were all investigated, with the result that the basement behavior can be accurately portrayed by a simple elastic model without the need for a more complex representation.

The results suggest that a longer substrate was involved in the bending process than the observed length of the basin, implying that the evolution of the North Louisiana basin can be better understood in the larger context of a "local" geological variation within the Gulf margin area.

Modeling of the flexural behavior of sections within the basin required that the hinge zone for flexing be located 100 to 200 km (60 to 120 mi) northwest of the study area. Alternatively, high initial angle of the unloaded plate, with too deep an initial depth, would have resulted in contradiction with known sedimentary facies patterns. The northwestward shift of the hinge line provides a consistent model for the region.

The flexural deformation was determined mainly by the rigidity of the plate (10^25±0.3Nm), the initial angle at the hinge point (-0.12°±0.03°), the initial bending moment (10^17.6±0.1N) at the free end of the plate, and the sediment load. Other parameters (initial end load, lateral stress, density contrast between the mantle and crust) are not dominant, indicating that the plate subsided mainly passively and that isostasy was less of a component relative to flexural strength.