Print this pageComplex Structural Reactivation Defined by Growth Strata
SHAW, JOHN H. , STEPHEN C. HOOK, and BUDI SATRIO
We present several examples of the structural reactivation of thrust faults and the complex inversion of normal faults that are defined by patterns of folded growth (syntectonic) strata imaged in seismic reflection profiles. Diagnostic patterns of growth strata are documented in both compressional and extensional structures that develop in one episode of deformation. Moreover, these growth structures are readily observed in inverted half grabens in which small amounts of shortening do not obscure the older rift architectures. In contrast, we present examples of structures developed through multiple episodes of slip on thrust faults that are recorded in refolded growth strata and unconformities. Kinematic restorations of balanced cross sections through these structures document the separate episodes of deformation and reveal structural geometries throughout the deformational history. These restorations can be used to define paleo-trap geometries, which are useful for high-grading structures in basins in which hydrocarbons migrated early in the tectonic history. In addition, we show examples of inverted half grabens with large amounts of shortening that obscure the primary basin geometry. in more common inversion structures, reverse displacements are relatively small and contractional folding is localized above the tip of the normal fault. In contrast, our examples have faults with large reverse displacements and substantial deformation within the half grabens. Kinematic restorations of the contractional deformations, guided by growth geometries, yield the shapes of the primary extensional structures. These restorations can define the timing of trap development and the evolution of hydrocarbon-charge pathways, which are often complex in basins in which source sediments were deposited in the highly deformed grabens.