ABSTRACT: Flexural Plate Inversion with Compressive Thrusting

Jie Tang, Ian Lerche, Jeff Cogan

A flexural plate inversion computer simulation models the characteristic patterns of subsidence, deformation, uplift, and erosion of basement under sediment load and compressive thrusting. The lithosphere is taken to be an elastic plate that deforms when a force is applied and returns to its original shape when the force is removed.

The program is effective in a given geological setting such as a foreland basin formed by compressive thrusting. The program is an inverse model that employs both nonlinear least squares and linear search techniques to determine the best values of the flexural parameters. Based on geological and geophysical data, dynamic ranges of parameters can be set to understand the influence of parameter changes on the evolution of foreland basins. Input data include a profile of the present-day basement. The parameters that determine the deformation of the basement are flexural rigidity (D), horizon compressive force (P), bending moment (M_o), applied initial load (V_o), dip angle (^Thgr) and added length (L) of the basement. The outputs are a profile of the deformed basement configuration that matches the present-day basement and a section of unloaded basin, which represents the basement geometry prior to any sediment or thrust loading in the section.

The result of synthetic data tests show that the model predicts (1) deformation and evolution of a foreland basin with sediment load and compressive thrusting; (2) unloaded basin geometry; (3) the strike of the unloaded basin and supply area of material into the basin; (4) the relationship between the original geometry of the basement and the distribution of lithofacies. Application to the Po basin, Italy, shows the following. (1) After the early Pliocene, the subsidence of the Po basin resulted from the sedimentation of the late Pliocene-Quaternary units and there is no sign of uplifting and exposure of upper Pliocene-Quaternary strata. Local or regional erosion of these strata must then be attributed to sea level change. (2) The characteristics of the unloaded basin geometry illustr te that the basin evolution is inherited because the later morphology generally repeats the early morphology. (3) The existence of the peripheral bulge at the late Miocene-early Pliocene has a significant relationship to the localization of hydrocarbons in the Po basin. (4) The original morphology of the basement controls the short-term distribution of lithofacies. In addition, the strike of Po basin and the provenance of sediment are inferred. The results show that incorporation of lateral stress offers new perspectives in the analysis and hydrocarbon exploration of sedimentary basins.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990