FAULT PATTERNS AND CONNECTIVITY ALONG EXTENSIONAL OBLIQUE AND LATERAL RAMPS: INSIGHTS FROM CLAY EXPERIMENTS

Listric growth faults in passive margin settings such as the Gulf of Mexico and Niger Delta are commonly characterized by lateral and oblique ramps, which may be attributed to pre-existing structural or stratigraphic discontinuities in the basin. Clay experiments have been used to model the geometry and connectivity of secondary faults formed along lateral and oblique ramps. Two sets of experiments with different offset angles were conducted, a lateral ramp configuration, with a 90° offset of the frontal ramp and an oblique ramp configuration, with a 30° offset. The lateral and oblique ramp configurations were created by offsets at the frontal edge of the fixed footwall base plate. Extension resulted in the formation of an expanding set of synthetic faults tied to the fixed footwall, and a corresponding set of antithetic faults tied to the moving hanging wall plate. A series of synthetic fault strands eventually connected to form the master fault. Characteristics such as fault orientation, fault density distribution, and the shape, size and distribution of the connected fault clusters vary with (1) the ramp offset angles, (2) structural position and (3) total extension. In map view, the secondary antithetic and synthetic faults mimic the geometry of the main fault, but the orientations of the secondary faults along the oblique or lateral ramps are approximately half the angle of the fault offset. With increasing total extension, the maximum cluster size of connected faults increases dramatically in the oblique and lateral segments, due to the intersection of fault sets of different orientations. These observations regarding fault orientations, density and connectivity provide insights on the structural geometry and mechanisms of formation of faults as well as the configuration of fault networks for fluid flow in passive margin settings.