Chapter 12 - Seismic expression of transpressional thick-skinned deformation in the southern foothills of Colombia

Abstract

In this work, we document three different modes of basement-involved contractional deformation. The first two show the positive inversion of a former half-graben basin, where a Cretaceous extensional event is later overprinted by Oligocene to Recent contraction resulting in basin inversion and fault reactivation. In the first example, the Guamal 3D seismic volume shows a footwall shortcut thrust, which accommodated shortening adjacent to a synrift normal fault that was not reactivated. In the second example for the Chichimene anticline, the main normal fault was reactivated during contraction, but the magnitude of subsequent fault displacement was so insufficient to change the sense of displacement along the trace of the fault, such that at depth, the fault maintained a normal sense of displacement. However, the upper segments show reverse displacement along the fault plane, which dies at an upper tip point, forming a fault propagation fold. In this case, we interpret a null point between the normal and the reverse fault segments. In the third example, the Castilla anticline is a broad anticline that is not associated with reactivation of preexisting normal faults; rather, it is associated with trishear fault propagation folding along a newly developed thrust fault. We show seismic evidence that reinforces different modes of deformation that can be associated with oblique stresses under transpressional deformation, including strain transfer associated with shortcut thrusts, fault reactivation across antecedent fault structures, and development of new thrust faults with complementary fault propagation folds.