Development of asymmetric basins along continental transform faults

Many basins associated with wrench or transform faults are asymmetrical, both longitudinally and laterally; the sense of basin asymmetry changes along the strike of transform faults. Geophysical data from the Dead Sea rift and other transforms indicate that wrench-induced asymmetric basins are bounded on only one side by a transform fault. This implies that, during the evolution of such basins, maximum compression was parallel to the transform. The direction of extension can change during the geologic evolution of a basin. A possible explanation of this observation takes the strength of the fault into into consideration. In the case of a weak fault in a strong crust, the horizontal principal stresses would probably rotate to orientations parallel and perpendicular to the fault, thus minimizing the shear stress on the main fault. Basins formed by regional extension, such as in the East African rift system, sometimes show similar features. Recent studies have shown that these basins often undergo oblique extension. This suggests that the asymmetry in these basins may result from simultaneous strike-slip motion and fault-normal extension, similar to the way asymmetry is produced in large transform basins. Periods of oblique extension can alternate with periods of orthogonal extension. The asymmetry formed during periods of oblique extension is often preserved in the stratigraphic record.