Dynamic restoration of profiles across diapiric salt structures: numericalapproach and its applications

The backstripping method that is widely used in basin analysis sometimes fa ils for salt-bearing basins because the highly mobile and buoyant salt defo rms its sedimentary overburden. We present a numerical approach for 2-D dyn amic restoration of cross-sections through successive earlier depositional stages. The approach is based on a solution of the inverse problem of the g ravitational (Rayleigh-Taylor) instability and combines the Galerkin-spline finite-element method with interface tracking and a backstripping method. Our model interprets basin profiles as multiple layers of viscous fluids wi th various densities and viscosities. The evolution of salt structures is m odelled backward in time by removing successively younger layers and restor ing older layers and any diapirs to the stage they were likely to have been . We test the sensitivity of the restoration technique to small variations in density of the layers at different stages in the evolution of diapiric s tructures. The applicability of the technique was demonstrated by reconstru ctions of upbuilt and downbuilt diapirs. The technique is used to restore a depth-converted seismic cross-section through the south-eastern part of th e Pricaspian salt basin. Mature salt diapirs in the section are shown to ha ve been downbuilt from a salt layer with an initially uniform thickness as a result of differential sedimentary loading until the end of the Triassic before one of the diapirs was buried and actively upbuilt. The numerical ap proach is well suited for restoration of cross-sections with ductile overbu rdens, but despite limitations can be developed to 3-D restorations and oth er rheologies. (C) 2001 Elsevier Science B.V. All rights reserved.