Abstract: Basement Motion and Sediment Loading: A Quantitative Study in Northern Louisiana, Gulf of Mexico

I. Csato, S. Cao, K. Petersen, I. Lerche, N. Sullivan, A. Lowrie

The North Louisiana basin is an interior basin in the northern part of the Gulf of Mexico passive margin that formed by rifting during the Middle Jurassic. Evaporites, transgressive carbonates, and continental to deltaic sediments accumulated after the rift phase. The basin infilling was not continuous in time, 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 plate led to flexural deformation.

The investigation reported here considers flexural modeling of the north Louisiana region during the postrift phase. Pure elastic, plastic-elastic, and thermo-elastic models were all applied, but resolution of parameters enabled the plate behavior to be accurately portrayed by just a simple elastic model without the need for more complex representations.

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

Modeling of the flexural behavior of sections within the basin required that the hinge zone for flexing be located 100-200 km northwest from the study area, else a 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 provided a consistent model for the region.

The flexural deformation was determined mainly by the rigidity of the plate (10^{25 ± 0.3}Nm), the tangent of the initial angle at the hinge point (-0.12 ± 0.03), the initial bending moment (10^{17 ± 0.1}N) at the free end of the plate, and the sediment load. Other parameters are not dominant (initial end load, lateral stress, density contrast between the mantle and crust), indicating that the plate subsided passively and that isostasy was not a major component relative to flexural strength.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994