Basement control on flexural profiles and the distribution of foreland facies: The Dwyka Group of the Karoo Basin, South Africa

Flexural partitioning of a foreland system into foredeep, forebulge, and backbulge is the result of the interplay of lithospheric deflection under orogenic loading (flexural tectonics) and the structure of the underlying basement. Flexural tectonics is commonly invoked as the sole control on flexural profiles, which are modeled as dampened sine curves with wavelengths and magnitudes controlled by a number of physical parameters of the lithosphere and the applied loads. Basement tectonics is shown here to be an equally important control on the scale and shape of flexural provinces, by controlling the location of flexural hinge lines and the tilt directions within the foreland system. The case study for this paper shows that basement heterogeneity coupled with the selective reactivation of major crustal faults may lead to distortion of the ideal flexural profile, by modifying the wavelength and shape of individual flexural provinces.